23 files changed, 3327 insertions, 0 deletions
diff --git a/svg-flatten/src/lambda_sink.cpp b/svg-flatten/src/lambda_sink.cpp
new file mode 100644
index 0000000..5172f24
--- /dev/null
+++ b/svg-flatten/src/lambda_sink.cpp
@@ -0,0 +1,36 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <cmath>
+#include <algorithm>
+#include <string>
+#include <gerbolyze.hpp>
+#include <svg_import_defs.h>
+
+using namespace gerbolyze;
+using namespace std;
+
+LambdaPolygonSink& LambdaPolygonSink::operator<<(const Polygon &poly) {
+    m_lambda(poly, m_currentPolarity);
+    return *this;
+}
+
+LambdaPolygonSink& LambdaPolygonSink::operator<<(GerberPolarityToken pol) {
+    m_currentPolarity = pol;
+    return *this;
+}
diff --git a/svg-flatten/src/main.cpp b/svg-flatten/src/main.cpp
new file mode 100644
index 0000000..135a4c1
--- /dev/null
+++ b/svg-flatten/src/main.cpp
@@ -0,0 +1,395 @@
+
+#include <cstdlib>
+#include <cstdio>
+#include <filesystem>
+#include <iostream>
+#include <fstream>
+#include <algorithm>
+#include <string>
+#include <argagg.hpp>
+#include <subprocess.h>
+#include <gerbolyze.hpp>
+#include "vec_core.h"
+#include <base64.h>
+
+using argagg::parser_results;
+using argagg::parser;
+using namespace std;
+using namespace gerbolyze;
+
+int main(int argc, char **argv) {
+    parser argparser {{
+            {"help", {"-h", "--help"},
+                "Print help and exit",
+                0},
+            {"version", {"-v", "--version"},
+                "Print version and exit",
+                0},
+            {"ofmt", {"-o", "--format"},
+                "Output format. Supported: gerber, svg, s-exp (KiCAD S-Expression)",
+                1},
+            {"precision", {"-p", "--precision"},
+                "Number of decimal places use for exported coordinates (gerber: 1-9, SVG: 0-*)",
+                1},
+            {"svg_clear_color", {"--clear-color"},
+                "SVG color to use for \"clear\" areas (default: white)",
+                1},
+            {"svg_dark_color", {"--dark-color"},
+                "SVG color to use for \"dark\" areas (default: black)",
+                1},
+            {"min_feature_size", {"-d", "--trace-space"},
+                "Minimum feature size of elements in vectorized graphics (trace/space) in mm. Default: 0.1mm.",
+                1},
+            {"no_header", {"--no-header"},
+                "Do not export output format header/footer, only export the primitives themselves",
+                0},
+            {"flatten", {"--flatten"},
+                "Flatten output so it only consists of non-overlapping white polygons. This perform composition at the vector level. Potentially slow.",
+                0},
+            {"no_flatten", {"--no-flatten"},
+                "Disable automatic flattening for KiCAD S-Exp export",
+                0},
+            {"dilate", {"--dilate"},
+                "Dilate output gerber primitives by this amount in mm. Used for masking out other layers.",
+                1},
+            {"only_groups", {"-g", "--only-groups"},
+                "Comma-separated list of group IDs to export.",
+                1},
+            {"vectorizer", {"-b", "--vectorizer"},
+                "Vectorizer to use for bitmap images. One of poisson-disc (default), hex-grid, square-grid, binary-contours, dev-null.",
+                1},
+            {"vectorizer_map", {"--vectorizer-map"},
+                "Map from image element id to vectorizer. Overrides --vectorizer. Format: id1=vectorizer,id2=vectorizer,...",
+                1},
+            {"force_svg", {"--force-svg"},
+                "Force SVG input irrespective of file name",
+                0},
+            {"force_png", {"--force-png"},
+                "Force bitmap graphics input irrespective of file name",
+                0},
+            {"size", {"-s", "--size"},
+                "Bitmap mode only: Physical size of output image in mm. Format: 12.34x56.78",
+                1},
+            {"sexp_mod_name", {"--sexp-mod-name"},
+                "Module name for KiCAD S-Exp output",
+                1},
+            {"sexp_layer", {"--sexp-layer"},
+                "Layer for KiCAD S-Exp output. Defaults to auto-detect layers from SVG layer/top-level group names",
+                1},
+            {"preserve_aspect_ratio", {"-a", "--preserve-aspect-ratio"},
+                "Bitmap mode only: Preserve aspect ratio of image. Allowed values are meet, slice. Can also parse full SVG preserveAspectRatio syntax.",
+                1},
+            {"skip_usvg", {"--no-usvg"},
+                "Do not preprocess input using usvg (do not use unless you know *exactly* what you're doing)",
+                0},
+            {"exclude_groups", {"-e", "--exclude-groups"},
+                "Comma-separated list of group IDs to exclude from export. Takes precedence over --only-groups.",
+                1},
+
+    }};
+
+
+    ostringstream usage;
+    usage
+        << argv[0] << " " << lib_version << endl
+        << endl
+        << "Usage: " << argv[0] << " [options]... [input_file] [output_file]" << endl
+        << endl
+        << "Specify \"-\" for stdin/stdout." << endl
+        << endl;
+
+    argagg::parser_results args;
+    try {
+        args = argparser.parse(argc, argv);
+    } catch (const std::exception& e) {
+        argagg::fmt_ostream fmt(cerr);
+        fmt << usage.str() << argparser << '\n'
+            << "Encountered exception while parsing arguments: " << e.what()
+            << '\n';
+        return EXIT_FAILURE;
+    }
+
+    if (args["help"]) {
+        argagg::fmt_ostream fmt(cerr);
+        fmt << usage.str() << argparser;
+        return EXIT_SUCCESS;
+    }
+
+    if (args["version"]) {
+        cerr << lib_version << endl;
+        return EXIT_SUCCESS;
+    }
+
+    string in_f_name;
+    istream *in_f = &cin;
+    ifstream in_f_file;
+    string out_f_name;
+    ostream *out_f = &cout;
+    ofstream out_f_file;
+
+    if (args.pos.size() >= 1) {
+        in_f_name = args.pos[0];
+
+        if (args.pos.size() >= 2) {
+            out_f_name = args.pos[1];
+        }
+    }
+
+    if (!in_f_name.empty() && in_f_name != "-") {
+        in_f_file.open(in_f_name);
+        if (!in_f_file) {
+            cerr << "Cannot open input file \"" << in_f_name << "\"" << endl;
+            return EXIT_FAILURE;
+        }
+        in_f = &in_f_file;
+    }
+
+    if (!out_f_name.empty() && out_f_name != "-") {
+        out_f_file.open(out_f_name);
+        if (!out_f_file) {
+            cerr << "Cannot open output file \"" << out_f_name << "\"" << endl;
+            return EXIT_FAILURE;
+        }
+        out_f = &out_f_file;
+    }
+
+    bool only_polys = args["no_header"];
+
+    int precision = 6;
+    if (args["precision"]) {
+        precision = atoi(args["precision"]);
+    }
+
+    string fmt = args["ofmt"] ? args["ofmt"] : "gerber";
+    transform(fmt.begin(), fmt.end(), fmt.begin(), [](unsigned char c){ return std::tolower(c); }); /* c++ yeah */
+
+    string sexp_layer = args["sexp_layer"] ? args["sexp_layer"].as<string>() : "auto";
+
+    bool force_flatten = false;
+    bool is_sexp = false;
+    PolygonSink *sink = nullptr;
+    PolygonSink *flattener = nullptr;
+    PolygonSink *dilater = nullptr;
+    if (fmt == "svg") {
+        string dark_color = args["svg_dark_color"] ? args["svg_dark_color"] : "#000000";
+        string clear_color = args["svg_clear_color"] ? args["svg_clear_color"] : "#ffffff";
+        sink = new SimpleSVGOutput(*out_f, only_polys, precision, dark_color, clear_color);
+
+    } else if (fmt == "gbr" || fmt == "grb" || fmt == "gerber") {
+        sink = new SimpleGerberOutput(*out_f, only_polys, 4, precision);
+
+    } else if (fmt == "s-exp" || fmt == "sexp" || fmt == "kicad") {
+        if (!args["sexp_mod_name"]) {
+            cerr << "--sexp-mod-name must be given for sexp export" << endl;
+            argagg::fmt_ostream fmt(cerr);
+            fmt << usage.str() << argparser;
+            return EXIT_FAILURE;
+        }
+
+        sink = new KicadSexpOutput(*out_f, args["sexp_mod_name"], sexp_layer, only_polys);
+        force_flatten = true;
+        is_sexp = true;
+
+    } else {
+        cerr << "Unknown output format \"" << fmt << "\"" << endl;
+        argagg::fmt_ostream fmt(cerr);
+        fmt << usage.str() << argparser;
+        return EXIT_FAILURE;
+    }
+
+    PolygonSink *top_sink = sink;
+
+    if (args["dilate"]) {
+        dilater = new Dilater(*top_sink, args["dilate"].as<double>());
+        top_sink = dilater;
+    }
+
+    if (args["flatten"] || (force_flatten && !args["no_flatten"])) {
+        flattener = new Flattener(*top_sink);
+        top_sink = flattener;
+    }
+
+    /* Because the C++ stdlib is bullshit */
+    auto id_match = [](string in, vector<string> &out) {
+        stringstream  ss(in);
+        while (getline(ss, out.emplace_back(), ',')) {
+        }
+        out.pop_back();
+    };
+
+    IDElementSelector sel;
+    if (args["only_groups"])
+        id_match(args["only_groups"], sel.include);
+    if (args["exclude_groups"])
+        id_match(args["exclude_groups"], sel.exclude);
+    if (is_sexp && sexp_layer == "auto") {
+        sel.layers = &gerbolyze::kicad_default_layers;
+    }
+
+    string vectorizer = args["vectorizer"] ? args["vectorizer"] : "poisson-disc";
+    /* Check argument */
+    ImageVectorizer *vec = makeVectorizer(vectorizer);
+    if (!vec) {
+        cerr << "Unknown vectorizer \"" << vectorizer << "\"." << endl;
+        argagg::fmt_ostream fmt(cerr);
+        fmt << usage.str() << argparser;
+        return EXIT_FAILURE;
+    }
+    delete vec;
+
+    double min_feature_size = 0.1; /* mm */
+    if (args["min_feature_size"]) {
+        min_feature_size = args["min_feature_size"].as<double>();
+    }
+
+    string ending = "";
+    auto idx = in_f_name.rfind(".");
+    if (idx != string::npos) {
+        ending = in_f_name.substr(idx);
+        transform(ending.begin(), ending.end(), ending.begin(), [](unsigned char c){ return std::tolower(c); }); /* c++ yeah */
+    }
+    
+    filesystem::path barf = { filesystem::temp_directory_path() /= (std::tmpnam(nullptr) + string(".svg")) };
+    filesystem::path frob = { filesystem::temp_directory_path() /= (std::tmpnam(nullptr) + string(".svg")) };
+
+    bool is_svg = args["force_svg"] || (ending == ".svg" && !args["force_png"]);
+    if (!is_svg) {
+        cerr << "writing bitmap into svg" << endl; 
+        if (!args["size"]) {
+            cerr << "Error: --size must be given when using bitmap input." << endl;
+            argagg::fmt_ostream fmt(cerr);
+            fmt << usage.str() << argparser;
+            return EXIT_FAILURE;
+        }
+
+        string sz = args["size"].as<string>();
+        auto pos = sz.find_first_of("x*,");
+        if (pos == string::npos) {
+            cerr << "Error: --size must be of form 12.34x56.78" << endl;
+            argagg::fmt_ostream fmt(cerr);
+            fmt << usage.str() << argparser;
+            return EXIT_FAILURE;
+        }
+
+        string x_str = sz.substr(0, pos);
+        string y_str = sz.substr(pos+1);
+
+        double width = std::strtod(x_str.c_str(), nullptr);
+        double height = std::strtod(y_str.c_str(), nullptr);
+
+        if (width < 1 || height < 1) {
+            cerr << "Error: --size must be of form 12.34x56.78 and values must be positive floating-point numbers in mm" << endl;
+            argagg::fmt_ostream fmt(cerr);
+            fmt << usage.str() << argparser;
+            return EXIT_FAILURE;
+        }
+
+        ofstream svg(barf.c_str());
+
+        svg << "<svg width=\"" << width << "mm\" height=\"" << height << "mm\" viewBox=\"0 0 "
+            << width << " " << height << "\" "
+            << "xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\">" << endl;
+
+        string par_attr = "none";
+        if (args["preserve_aspect_ratio"]) {
+            string aspect_ratio = args["preserve_aspect_ratio"].as<string>();
+            if (aspect_ratio == "meet") {
+                par_attr = "xMidYMid meet";
+            } else if (aspect_ratio == "slice") {
+                par_attr = "xMidYMid slice";
+            } else {
+                par_attr = aspect_ratio;
+            }
+        }
+        svg << "<image width=\"" << width << "\" height=\"" << height << "\" x=\"0\" y=\"0\" preserveAspectRatio=\""
+            << par_attr << "\" xlink:href=\"data:image/png;base64,";
+        
+        /* c++ has the best hacks */
+        std::ostringstream sstr;
+        sstr << in_f->rdbuf();
+        string le_data = sstr.str();
+
+        svg << base64_encode(le_data);
+        svg << "\"/>" << endl;
+
+        svg << "</svg>" << endl;
+        svg.close();
+
+    } else { /* svg file */
+        cerr << "copying svg input into temp svg" << endl; 
+
+        /* c++ has the best hacks */
+        std::ostringstream sstr;
+        sstr << in_f->rdbuf();
+
+        ofstream tmp_out(barf.c_str());
+        tmp_out << sstr.str();
+        tmp_out.close();
+
+    }
+
+    if (args["skip_usvg"]) {
+        cerr << "skipping usvg" << endl; 
+        frob = barf;
+
+    } else {
+        cerr << "calling usvg on " << barf << " and " << frob << endl; 
+        const char *command_line[] = {"usvg", "--keep-named-groups", barf.c_str(), frob.c_str(), NULL};
+        struct subprocess_s subprocess;
+        int rc = subprocess_create(command_line, subprocess_option_inherit_environment, &subprocess);
+        if (rc) {
+            cerr << "Error calling usvg!" << endl;
+            return EXIT_FAILURE;
+        }
+
+        int usvg_rc = 0;
+        rc = subprocess_join(&subprocess, &usvg_rc);
+        if (rc) {
+            cerr << "Error calling usvg!" << endl;
+            return EXIT_FAILURE;
+        }
+        if (usvg_rc) {
+            cerr << "usvg returned an error code: " << usvg_rc << endl;
+            return EXIT_FAILURE;
+        }
+
+        rc = subprocess_destroy(&subprocess);
+        if (rc) {
+            cerr << "Error calling usvg!" << endl;
+            return EXIT_FAILURE;
+        }
+    }
+
+    VectorizerSelectorizer vec_sel(vectorizer, args["vectorizer_map"] ? args["vectorizer_map"] : "");
+    RenderSettings rset {
+        min_feature_size,
+        vec_sel,
+    };
+
+    SVGDocument doc;
+    cerr << "Loading temporary file " << frob << endl;
+    ifstream load_f(frob);
+    if (!doc.load(load_f)) {
+        cerr <<  "Error loading input file \"" << in_f_name << "\", exiting." << endl;
+        return EXIT_FAILURE;
+    }
+
+    doc.render(rset, *top_sink, &sel);
+
+    if (!is_svg) {
+        remove(frob.c_str());
+        remove(barf.c_str());
+    }
+
+    if (flattener) {
+        delete flattener;
+    }
+    if (dilater) {
+        delete dilater;
+    }
+    if (sink) {
+        delete sink;
+    }
+    return EXIT_SUCCESS;
+}
+
diff --git a/svg-flatten/src/out_dilater.cpp b/svg-flatten/src/out_dilater.cpp
new file mode 100644
index 0000000..c0e5969
--- /dev/null
+++ b/svg-flatten/src/out_dilater.cpp
@@ -0,0 +1,90 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <cmath>
+#include <algorithm>
+#include <string>
+#include <iostream>
+#include <iomanip>
+#include <gerbolyze.hpp>
+#include <clipper.hpp>
+#include <svg_import_defs.h>
+#include <svg_geom.h>
+#include "polylinecombine.hpp"
+
+using namespace gerbolyze;
+using namespace std;
+
+void Dilater::header(d2p origin, d2p size) {
+    m_sink.header(origin, size);
+}
+
+void Dilater::footer() {
+    m_sink.footer();
+}
+
+Dilater &Dilater::operator<<(const LayerNameToken &layer_name) {
+    m_sink << layer_name;
+
+    return *this;
+}
+
+Dilater &Dilater::operator<<(GerberPolarityToken pol) {
+    m_current_polarity = pol;
+    m_sink << pol;
+
+    return *this;
+}
+
+Dilater &Dilater::operator<<(const Polygon &poly) {
+    static int i = 0;
+    cerr << "dilating poly " << i++ << endl;
+
+    cerr << "got poly of " << poly.size() << " nodes" << endl;
+    ClipperLib::Path poly_c;
+    for (auto &p : poly) {
+        poly_c.push_back({(ClipperLib::cInt)round(p[0] * clipper_scale), (ClipperLib::cInt)round(p[1] * clipper_scale)});
+    }
+
+    ClipperLib::ClipperOffset offx;
+    offx.ArcTolerance = 0.01 * clipper_scale; /* 10µm; TODO: Make this configurable */
+    offx.AddPath(poly_c, ClipperLib::jtRound, ClipperLib::etClosedPolygon);
+    double dilation = m_dilation;
+    if (m_current_polarity == GRB_POL_CLEAR) {
+        dilation = -dilation;
+    }
+
+    ClipperLib::PolyTree solution; 
+    offx.Execute(solution, dilation * clipper_scale);
+
+    ClipperLib::Paths c_nice_polys;
+    dehole_polytree(solution, c_nice_polys);
+
+    for (auto &nice_poly : c_nice_polys) {
+        Polygon new_poly;
+        for (auto &p : nice_poly) {
+            new_poly.push_back({
+                    (double)p.X / clipper_scale,
+                    (double)p.Y / clipper_scale });
+        }
+        m_sink << new_poly;
+    }
+
+    return *this;
+}
+
diff --git a/svg-flatten/src/out_flattener.cpp b/svg-flatten/src/out_flattener.cpp
new file mode 100644
index 0000000..8868ca2
--- /dev/null
+++ b/svg-flatten/src/out_flattener.cpp
@@ -0,0 +1,187 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <cmath>
+#include <algorithm>
+#include <string>
+#include <iostream>
+#include <iomanip>
+#include <gerbolyze.hpp>
+#include <svg_import_defs.h>
+#include <svg_geom.h>
+#include "polylinecombine.hpp"
+
+using namespace gerbolyze;
+using namespace std;
+
+static void polygon_to_cavc (const Polygon &in, cavc::Polyline<double> &out) {
+    for (auto &p : in) {
+        out.addVertex(p[0], p[1], 0);
+    }
+    out.isClosed() = true; /* sic! */
+}
+
+static void cavc_to_polygon (const cavc::Polyline<double> &in, Polygon &out) {
+    for (auto &p : in.vertexes()) {
+        out.emplace_back(d2p{p.x(), p.y()});
+    }
+}
+
+namespace gerbolyze {
+    class Flattener_D {
+    public:
+        vector<cavc::Polyline<double>> dark_polys;
+        vector<cavc::Polyline<double>> clear_polys;
+
+        void add_dark_polygon(const Polygon &in) {
+            polygon_to_cavc(in, dark_polys.emplace_back());
+        }
+
+        void add_clear_polygon(const Polygon &in) {
+            polygon_to_cavc(in, clear_polys.emplace_back());
+        }
+    };
+}
+
+Flattener::Flattener(PolygonSink &sink) : m_sink(sink) {
+    d = new Flattener_D();
+}
+
+Flattener::~Flattener() {
+    delete d;
+}
+
+void Flattener::header(d2p origin, d2p size) {
+    m_sink.header(origin, size);
+}
+
+void Flattener::render_out_clear_polys() {
+    for (auto &sub : d->clear_polys) {
+        vector<cavc::Polyline<double>> new_dark_polys;
+        new_dark_polys.reserve(d->dark_polys.size());
+
+        for (cavc::Polyline<double> cavc_in : d->dark_polys) {
+            auto res = cavc::combinePolylines(cavc_in, sub, cavc::PlineCombineMode::Exclude);
+
+            if (res.subtracted.size() == 0) {
+                for (auto &rem : res.remaining) {
+                    new_dark_polys.push_back(std::move(rem));
+                }
+
+            } else { /* custom one-hole deholing code */
+                assert (res.remaining.size() == 1);
+                assert (res.subtracted.size() == 1);
+
+                auto &rem = res.remaining[0];
+                auto &sub = res.subtracted[0];
+                auto bbox = getExtents(rem);
+
+                cavc::Polyline<double> quad;
+                quad.addVertex(bbox.xMin, bbox.yMin, 0);
+                if (sub.vertexes()[0].x() < sub.vertexes()[1].x()) {
+                    quad.addVertex(sub.vertexes()[0]);
+                    quad.addVertex(sub.vertexes()[1]);
+                } else {
+                    quad.addVertex(sub.vertexes()[1]);
+                    quad.addVertex(sub.vertexes()[0]);
+                }
+                quad.addVertex(bbox.xMax, bbox.yMin, 0);
+                quad.isClosed() = true; /* sic! */
+
+                auto res2 = cavc::combinePolylines(rem, quad, cavc::PlineCombineMode::Exclude);
+                assert (res2.subtracted.size() == 0);
+
+                for (auto &rem : res2.remaining) {
+                    auto res3 = cavc::combinePolylines(rem, sub, cavc::PlineCombineMode::Exclude);
+                    assert (res3.subtracted.size() == 0);
+                    for (auto &p : res3.remaining) {
+                        new_dark_polys.push_back(std::move(p));
+                    }
+                }
+
+                auto res4 = cavc::combinePolylines(rem, quad, cavc::PlineCombineMode::Intersect);
+                assert (res4.subtracted.size() == 0);
+
+                for (auto &rem : res4.remaining) {
+                    auto res5 = cavc::combinePolylines(rem, sub, cavc::PlineCombineMode::Exclude);
+                    assert (res5.subtracted.size() == 0);
+                    for (auto &p : res5.remaining) {
+                        new_dark_polys.push_back(std::move(p));
+                    }
+                }
+            }
+        }
+
+        d->dark_polys = std::move(new_dark_polys);
+    }
+    d->clear_polys.clear();
+}
+
+Flattener &Flattener::operator<<(GerberPolarityToken pol) {
+    if (m_current_polarity != pol) {
+        m_current_polarity = pol;
+
+        if (pol == GRB_POL_DARK) {
+            render_out_clear_polys();
+        }
+    }
+
+    return *this;
+}
+
+Flattener &Flattener::operator<<(const LayerNameToken &layer_name) {
+    flush_polys_to_sink();
+    m_sink << layer_name;
+    cerr << "Flattener forwarding layer name to sink: \"" << layer_name.m_name << "\"" << endl;
+
+    return *this;
+}
+
+Flattener &Flattener::operator<<(const Polygon &poly) {
+    if (m_current_polarity == GRB_POL_DARK) {
+        d->add_dark_polygon(poly);
+
+    } else { /* clear */
+        d->add_clear_polygon(poly);
+        render_out_clear_polys();
+    }
+
+    return *this;
+}
+
+void Flattener::flush_polys_to_sink() {
+    *this << GRB_POL_DARK; /* force render */
+    m_sink << GRB_POL_DARK;
+
+    for (auto &poly : d->dark_polys) {
+        Polygon poly_out;
+        for (auto &p : poly.vertexes()) {
+            poly_out.emplace_back(d2p{p.x(), p.y()});
+        }
+        m_sink << poly_out;
+    }
+
+    d->clear_polys.clear();
+    d->dark_polys.clear();
+}
+
+void Flattener::footer() {
+    flush_polys_to_sink();
+    m_sink.footer();
+}
+
diff --git a/svg-flatten/src/out_gerber.cpp b/svg-flatten/src/out_gerber.cpp
new file mode 100644
index 0000000..c320184
--- /dev/null
+++ b/svg-flatten/src/out_gerber.cpp
@@ -0,0 +1,99 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <cmath>
+#include <algorithm>
+#include <string>
+#include <iostream>
+#include <iomanip>
+#include <gerbolyze.hpp>
+#include <svg_import_defs.h>
+
+using namespace gerbolyze;
+using namespace std;
+
+SimpleGerberOutput::SimpleGerberOutput(ostream &out, bool only_polys, int digits_int, int digits_frac, d2p offset)
+    : StreamPolygonSink(out, only_polys),
+    m_digits_int(digits_int),
+    m_digits_frac(digits_frac),
+    m_offset(offset)
+{
+    assert(1 <= digits_int && digits_int <= 9);
+    assert(0 <= digits_frac && digits_frac <= 9);
+    m_gerber_scale = round(pow(10, m_digits_frac));
+}
+
+void SimpleGerberOutput::header_impl(d2p origin, d2p size) {
+    m_offset[0] += origin[0];
+    m_offset[1] += origin[1];
+    m_width = size[0] - origin[0];
+    m_height = size[1] - origin[1];
+    
+    if (pow(10, m_digits_int-1) < max(m_width, m_height)) {
+        cerr << "Warning: Input has bounding box too large for " << m_digits_int << "." << m_digits_frac << " gerber resolution!" << endl;
+    }
+
+    m_out << "%FSLAX" << m_digits_int << m_digits_frac << "Y" << m_digits_int << m_digits_frac << "*%" << endl;
+    m_out << "%MOMM*%" << endl;
+    m_out << "%LPD*%" << endl;
+    m_out << "G01*" << endl;
+    m_out << "%ADD10C,0.050000*%" << endl;
+    m_out << "D10*" << endl;
+}
+
+SimpleGerberOutput& SimpleGerberOutput::operator<<(GerberPolarityToken pol) {
+    if (pol == GRB_POL_DARK) {
+        m_out << "%LPD*%" << endl;
+    } else if (pol == GRB_POL_CLEAR) {
+        m_out << "%LPC*%" << endl;
+    } else {
+        assert(false);
+    }
+
+    return *this;
+}
+SimpleGerberOutput& SimpleGerberOutput::operator<<(const Polygon &poly) {
+    if (poly.size() < 3) {
+        cerr << "Warning: " << poly.size() << "-element polygon passed to SimpleGerberOutput" << endl;
+        return *this;
+    }
+
+    /* NOTE: Clipper and gerber both have different fixed-point scales. We get points in double mm. */
+    double x = round((poly[0][0] + m_offset[0]) * m_gerber_scale);
+    double y = round((m_height - poly[0][1] + m_offset[1]) * m_gerber_scale);
+    m_out << "G36*" << endl;
+    m_out << "X" << setw(m_digits_int + m_digits_frac) << setfill('0') << (long long int)x
+          << "Y" << setw(m_digits_int + m_digits_frac) << setfill('0') << (long long int)y
+          << "D02*" << endl;
+    m_out << "G01*" << endl;
+    for (size_t i=1; i<poly.size(); i++) {
+        double x = round((poly[i][0] + m_offset[0]) * m_gerber_scale);
+        double y = round((m_height - poly[i][1] + m_offset[1]) * m_gerber_scale);
+        m_out << "X" << setw(m_digits_int + m_digits_frac) << setfill('0') << (long long int)x
+              << "Y" << setw(m_digits_int + m_digits_frac) << setfill('0') << (long long int)y
+              << "D01*" << endl;
+    }
+    m_out << "G37*" << endl;
+
+    return *this;
+}
+
+void SimpleGerberOutput::footer_impl() {
+    m_out << "M02*" << endl;
+}
+
diff --git a/svg-flatten/src/out_sexp.cpp b/svg-flatten/src/out_sexp.cpp
new file mode 100644
index 0000000..9a04416
--- /dev/null
+++ b/svg-flatten/src/out_sexp.cpp
@@ -0,0 +1,108 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <cmath>
+#include <algorithm>
+#include <string>
+#include <iostream>
+#include <iomanip>
+#include <gerbolyze.hpp>
+#include <svg_import_defs.h>
+#include <ctime>
+
+using namespace gerbolyze;
+using namespace std;
+
+
+KicadSexpOutput::KicadSexpOutput(ostream &out, string mod_name, string layer, bool only_polys, string ref_text, string val_text, d2p ref_pos, d2p val_pos)
+    : StreamPolygonSink(out, only_polys),
+    m_mod_name(mod_name),
+    m_layer(layer == "auto" ? "unknown" : layer),
+    m_auto_layer(layer == "auto"),
+    m_val_text(val_text),
+    m_ref_pos(ref_pos),
+    m_val_pos(val_pos)
+{
+    if (ref_text.empty()) {
+        m_ref_text = mod_name;
+    } else {
+        m_ref_text = ref_text;
+    }
+}
+
+void KicadSexpOutput::header_impl(d2p, d2p) {
+    auto tedit = std::time(0);
+    m_out << "(module " << m_mod_name << " (layer F.Cu) (tedit " << std::hex << std::setfill('0') << std::setw(8) << tedit << ")" << endl;
+    m_out << "  (fp_text reference " << m_ref_text << " (at " << m_ref_pos[0] << " " << m_ref_pos[1] << ") (layer F.SilkS) hide" << endl;
+    m_out << "    (effects (font (size 1 1) (thickness 0.15)))" << endl;
+    m_out << "  )" << endl;
+    m_out << "  (fp_text value " << m_val_text << " (at " << m_val_pos[0] << " " << m_val_pos[1] << ") (layer F.SilkS) hide" << endl;
+    m_out << "    (effects (font (size 1 1) (thickness 0.15)))" << endl;
+    m_out << "  )" << endl;
+}
+
+KicadSexpOutput &KicadSexpOutput::operator<<(GerberPolarityToken pol) {
+    if (pol == GRB_POL_CLEAR) {
+        cerr << "Warning: clear polarity not supported since KiCAD manages to have an even worse graphics model than gerber, except it can't excuse itself by its age..... -.-" << endl;
+    }
+
+    return *this;
+}
+
+KicadSexpOutput &KicadSexpOutput::operator<<(const LayerNameToken &layer_name) {
+    if (!m_auto_layer)
+        return *this;
+
+    cerr << "Setting S-Exp export layer to \"" << layer_name.m_name << "\"" << endl;
+    if (!layer_name.m_name.empty()) {
+        m_layer = layer_name.m_name;
+    } else {
+        m_layer = "unknown";
+    }
+
+    return *this;
+}
+
+KicadSexpOutput &KicadSexpOutput::operator<<(const Polygon &poly) {
+    if (m_auto_layer) {
+        if (std::find(m_export_layers->begin(), m_export_layers->end(), m_layer) == m_export_layers->end()) {
+            cerr << "Rejecting S-Exp export layer \"" << m_layer << "\"" << endl;
+            return *this;
+        }
+    }
+
+    if (poly.size() < 3) {
+        cerr << "Warning: " << poly.size() << "-element polygon passed to KicadSexpOutput" << endl;
+        return *this;
+    }
+
+    m_out << "  (fp_poly (pts";
+    for (auto &p : poly) {
+        m_out << " (xy " << p[0] << " " << p[1] << ")";
+    }
+    m_out << ")";
+    m_out << " (layer " << m_layer << ") (width 0))" << endl;
+
+    return *this;
+}
+
+void KicadSexpOutput::footer_impl() {
+    m_out << ")" << endl;
+}
+
+
diff --git a/svg-flatten/src/out_svg.cpp b/svg-flatten/src/out_svg.cpp
new file mode 100644
index 0000000..159bf13
--- /dev/null
+++ b/svg-flatten/src/out_svg.cpp
@@ -0,0 +1,80 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <cmath>
+#include <algorithm>
+#include <string>
+#include <iostream>
+#include <iomanip>
+#include <gerbolyze.hpp>
+#include <svg_import_defs.h>
+
+using namespace gerbolyze;
+using namespace std;
+
+SimpleSVGOutput::SimpleSVGOutput(ostream &out, bool only_polys, int digits_frac, string dark_color, string clear_color)
+    : StreamPolygonSink(out, only_polys),
+    m_digits_frac(digits_frac),
+    m_dark_color(dark_color),
+    m_clear_color(clear_color),
+    m_current_color(dark_color)
+{
+}
+
+void SimpleSVGOutput::header_impl(d2p origin, d2p size) {
+    m_offset[0] = origin[0];
+    m_offset[1] = origin[1];
+    m_out << "<svg width=\"" << size[0] << "mm\" height=\"" << size[1] << "mm\" viewBox=\"0 0 "
+        << size[0] << " " << size[1] << "\" xmlns=\"http://www.w3.org/2000/svg\">" << endl;
+}
+
+SimpleSVGOutput &SimpleSVGOutput::operator<<(GerberPolarityToken pol) {
+    if (pol == GRB_POL_DARK) {
+        m_current_color = m_dark_color;
+    } else if (pol == GRB_POL_CLEAR) {
+        m_current_color = m_clear_color;
+    } else {
+        assert(false);
+    }
+
+    return *this;
+}
+
+SimpleSVGOutput &SimpleSVGOutput::operator<<(const Polygon &poly) {
+    if (poly.size() < 3) {
+        cerr << "Warning: " << poly.size() << "-element polygon passed to SimpleGerberOutput" << endl;
+        return *this;
+    }
+
+    m_out << "<path fill=\"" << m_current_color << "\" d=\"";
+    m_out << "M " << setprecision(m_digits_frac) << (poly[0][0] + m_offset[0])
+          << " " << setprecision(m_digits_frac) << (poly[0][1] + m_offset[1]);
+    for (size_t i=1; i<poly.size(); i++) {
+        m_out << " L " << setprecision(m_digits_frac) << (poly[i][0] + m_offset[0])
+              << " " << setprecision(m_digits_frac) << (poly[i][1] + m_offset[1]);
+    }
+    m_out << " Z";
+    m_out << "\"/>" << endl;
+
+    return *this;
+}
+
+void SimpleSVGOutput::footer_impl() {
+    m_out << "</svg>" << endl;
+}
+
diff --git a/svg-flatten/src/svg_color.cpp b/svg-flatten/src/svg_color.cpp
new file mode 100644
index 0000000..5f1d693
--- /dev/null
+++ b/svg-flatten/src/svg_color.cpp
@@ -0,0 +1,119 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "svg_color.h"
+
+#include <assert.h>
+#include <string>
+#include <cmath>
+
+using namespace gerbolyze;
+using namespace std;
+
+/* Map an SVG fill or stroke definition (color, but may also be a pattern) to a gerber color.
+ *
+ * This function handles transparency: Transparent SVG colors are mapped such that no gerber output is generated for
+ * them.
+ */
+enum gerber_color gerbolyze::svg_color_to_gerber(string color, string opacity, enum gerber_color default_val) {
+    float alpha = 1.0;
+    if (!opacity.empty() && opacity[0] != '\0') {
+        char *endptr = nullptr;
+        alpha = strtof(opacity.data(), &endptr);
+        assert(endptr);
+        assert(*endptr == '\0');
+    }
+
+    if (alpha < 0.5f) {
+        return GRB_NONE;
+    }
+
+    if (color.empty()) {
+        return default_val;
+    }
+
+    if (color == "none") {
+        return GRB_NONE;
+    }
+
+    if (color.rfind("url(#", 0) != string::npos) {
+        return GRB_PATTERN_FILL;
+    }
+
+    if (color.length() == 7 && color[0] == '#') {
+        HSVColor hsv(color);
+        if (hsv.v >= 0.5) {
+            return GRB_CLEAR;
+        }
+    }
+
+    return GRB_DARK;
+}
+
+gerbolyze::RGBColor::RGBColor(string hex) {
+    assert(hex[0] == '#');
+    char *endptr = nullptr;
+    const char *c = hex.data();
+    int rgb = strtol(c + 1, &endptr, 16);
+    assert(endptr);
+    assert(endptr == c + 7);
+    assert(*endptr == '\0');
+    r = ((rgb >> 16) & 0xff) / 255.0f;
+    g = ((rgb >>  8) & 0xff) / 255.0f;
+    b = ((rgb >>  0) & 0xff) / 255.0f;
+};
+
+gerbolyze::HSVColor::HSVColor(const RGBColor &color) {
+    float xmax = fmax(color.r, fmax(color.g, color.b));
+    float xmin = fmin(color.r, fmin(color.g, color.b));
+    float c = xmax - xmin;
+
+    v = xmax;
+
+    if (c == 0)
+        h = 0;
+    else if (v == color.r)
+        h = 1/3 * (0 + (color.g - color.b) / c);
+    else if (v == color.g)
+        h = 1/3 * (2 + (color.b - color.r) / c);
+    else //  v == color.b
+        h = 1/3 * (4 + (color.r - color.g) / c);
+
+    s = (v == 0) ? 0 : (c/v);
+}
+
+/* Invert gerber color */
+enum gerber_color gerbolyze::gerber_color_invert(enum gerber_color color) {
+    switch (color) {
+        case GRB_CLEAR: return GRB_DARK;
+        case GRB_DARK: return GRB_CLEAR;
+        default: return color; /* none, pattern */
+    }
+}
+
+/* Read node's fill attribute and convert it to a gerber color */
+enum gerber_color gerbolyze::gerber_fill_color(const pugi::xml_node &node) {
+    return svg_color_to_gerber(node.attribute("fill").value(), node.attribute("fill-opacity").value(), GRB_DARK);
+}
+
+/* Read node's stroke attribute and convert it to a gerber color */
+enum gerber_color gerbolyze::gerber_stroke_color(const pugi::xml_node &node) {
+    return svg_color_to_gerber(node.attribute("stroke").value(), node.attribute("stroke-opacity").value(), GRB_NONE);
+}
+
+
diff --git a/svg-flatten/src/svg_color.h b/svg-flatten/src/svg_color.h
new file mode 100644
index 0000000..2817cd9
--- /dev/null
+++ b/svg-flatten/src/svg_color.h
@@ -0,0 +1,51 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <pugixml.hpp>
+
+namespace gerbolyze {
+
+/* Enum that describes the color with which an SVG primite should be exported */
+enum gerber_color { 
+    GRB_NONE = 0,
+    GRB_CLEAR,
+    GRB_DARK,
+    GRB_PATTERN_FILL,
+};
+
+class RGBColor {
+public:
+    float r, g, b;
+    RGBColor(std::string hex);
+};
+
+class HSVColor {
+public:
+    float h, s, v;
+    HSVColor(const RGBColor &color);
+};
+
+enum gerber_color svg_color_to_gerber(std::string color, std::string opacity, enum gerber_color default_val);
+enum gerber_color gerber_color_invert(enum gerber_color color);
+enum gerber_color gerber_fill_color(const pugi::xml_node &node);
+enum gerber_color gerber_stroke_color(const pugi::xml_node &node);
+
+} /* namespace gerbolyze */
+
diff --git a/svg-flatten/src/svg_doc.cpp b/svg-flatten/src/svg_doc.cpp
new file mode 100644
index 0000000..3b253be
--- /dev/null
+++ b/svg-flatten/src/svg_doc.cpp
@@ -0,0 +1,539 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <iostream>
+#include <fstream>
+
+#include <gerbolyze.hpp>
+#include "svg_import_defs.h"
+#include "svg_color.h"
+#include "svg_geom.h"
+#include "svg_path.h"
+#include "vec_core.h"
+
+using namespace gerbolyze;
+using namespace std;
+using namespace ClipperLib;
+
+gerbolyze::SVGDocument::~SVGDocument() {
+    if (cr)
+        cairo_destroy (cr);
+    if (surface)
+        cairo_surface_destroy (surface);
+}
+
+bool gerbolyze::SVGDocument::load(string filename, string debug_out_filename) {
+    ifstream in_f;
+    in_f.open(filename);
+
+    return in_f && load(in_f, debug_out_filename);
+}
+
+bool gerbolyze::SVGDocument::load(istream &in, string debug_out_filename) {
+    /* Load XML document */
+    auto res = svg_doc.load(in);
+    if (!res) {
+        cerr << "Cannot parse input file" << endl;
+        return false;
+    }
+
+    root_elem = svg_doc.child("svg");
+    if (!root_elem) {
+        cerr << "Input file is missing root <svg> element" << endl;
+        return false;
+    }
+
+    /* Set up the document's viewport transform */
+    istringstream vb_stream(root_elem.attribute("viewBox").value());
+    vb_stream >> vb_x >> vb_y >> vb_w >> vb_h;
+    cerr << "loaded viewbox: " << vb_x << ", " << vb_y << ", " << vb_w << ", " << vb_h << endl;
+
+    page_w = usvg_double_attr(root_elem, "width");
+    page_h = usvg_double_attr(root_elem, "height");
+    /* usvg resolves all units, but instead of outputting some reasonable absolute length like mm, it converts
+     * everything to px, which depends on usvg's DPI setting (--dpi).
+     */
+    page_w_mm = page_w / assumed_usvg_dpi * 25.4;
+    page_h_mm = page_h / assumed_usvg_dpi * 25.4;
+    if (!(page_w_mm > 0.0 && page_h_mm > 0.0 && page_w_mm < 10e3 && page_h_mm < 10e3)) {
+        cerr << "Warning: Page has zero or negative size, or is larger than 10 x 10 meters! Parsed size: " << page_w << " x " << page_h << " millimeter" << endl;
+    }
+
+    if (fabs((vb_w / page_w) / (vb_h / page_h) - 1.0) > 0.001) {
+        cerr << "Warning: Document has different document unit scale in x and y direction! Output will likely be garbage!" << endl;
+    }
+
+    /* Get the one document defs element */
+    defs_node = root_elem.child("defs");
+    if (!defs_node) {
+        cerr << "Warning: Input file is missing <defs> node" << endl;
+    }
+
+    setup_debug_output(debug_out_filename);
+    setup_viewport_clip();
+    load_clips();
+    load_patterns();
+
+    _valid = true;
+    return true;
+}
+
+const Paths *gerbolyze::SVGDocument::lookup_clip_path(const pugi::xml_node &node) {
+    string id(usvg_id_url(node.attribute("clip-path").value()));
+    if (id.empty() || !clip_path_map.contains(id)) {
+        return nullptr;
+    }
+    return &clip_path_map[id];
+}
+
+Pattern *gerbolyze::SVGDocument::lookup_pattern(const string id) {
+    if (id.empty() || !pattern_map.contains(id)) {
+        return nullptr;
+    }
+    return &pattern_map[id];
+};
+
+/* Used to convert mm values from configuration such as the minimum feature size into document units. */
+double gerbolyze::SVGDocument::mm_to_doc_units(double mm) const {
+    return mm * (vb_w / page_w_mm);
+}
+
+double gerbolyze::SVGDocument::doc_units_to_mm(double px) const {
+    return px / (vb_w / page_w_mm);
+}
+
+bool IDElementSelector::match(const pugi::xml_node &node, bool included, bool is_root) const {
+    string id = node.attribute("id").value();
+    if (is_root && layers) {
+        bool layer_match = std::find(layers->begin(), layers->end(), id) != layers->end();
+        if (!layer_match) {
+            cerr << "Rejecting layer \"" << id << "\"" << endl;
+            return false;
+        }
+    }
+
+    if (include.empty() && exclude.empty())
+        return true;
+
+    bool include_match = std::find(include.begin(), include.end(), id) != include.end();
+    bool exclude_match = std::find(exclude.begin(), exclude.end(), id) != exclude.end();
+
+    if (exclude_match || (!included && !include_match)) {
+        return false;
+    }
+
+    return true;
+}
+
+/* Recursively export all SVG elements in the given group. */
+void gerbolyze::SVGDocument::export_svg_group(const RenderSettings &rset, const pugi::xml_node &group, Paths &parent_clip_path, const ElementSelector *sel, bool included, bool is_root) {
+    /* Enter the group's coordinate system */
+    cairo_save(cr);
+    apply_cairo_transform_from_svg(cr, group.attribute("transform").value());
+    
+    /* Fetch clip path from global registry and transform it into document coordinates. */
+    Paths clip_path;
+    auto *lookup = lookup_clip_path(group);
+    if (!lookup) {
+        string id(usvg_id_url(group.attribute("clip-path").value()));
+        if (!id.empty()) {
+            cerr << "Warning: Cannot find clip path with ID \"" << group.attribute("clip-path").value() << "\" for group \"" << group.attribute("id").value() << "\"." << endl;
+        }
+
+    } else {
+        clip_path = *lookup;
+    }
+    transform_paths(cr, clip_path);
+
+    /* Clip against parent's clip path (both are now in document coordinates) */
+    if (!parent_clip_path.empty()) {
+        if (!clip_path.empty()) {
+            combine_clip_paths(parent_clip_path, clip_path, clip_path);
+        } else {
+            clip_path = parent_clip_path;
+        }
+    }
+
+    /* Iterate over the group's children, exporting them one by one. */
+    for (const auto &node : group.children()) {
+        if (sel && !sel->match(node, included, is_root))
+            continue;
+
+        string name(node.name());
+        if (name == "g") {
+            if (is_root) { /* Treat top-level groups as "layers" like inkscape does. */
+                cerr << "Forwarding layer name to sink: \"" << node.attribute("id").value() << "\"" << endl;
+                LayerNameToken tok { node.attribute("id").value() };
+                *polygon_sink << tok;
+            }
+
+            export_svg_group(rset, node, clip_path, sel, true);
+            
+            if (is_root) {
+                LayerNameToken tok {""};
+                *polygon_sink << tok;
+            }
+
+        } else if (name == "path") {
+            export_svg_path(rset, node, clip_path);
+
+        } else if (name == "image") {
+            ImageVectorizer *vec = rset.m_vec_sel.select(node);
+            if (!vec) {
+                cerr << "Cannot resolve vectorizer for node \"" << node.attribute("id").value() << "\"" << endl;
+                continue;
+            }
+
+            double min_feature_size_px = mm_to_doc_units(rset.m_minimum_feature_size_mm);
+            vec->vectorize_image(cr, node, clip_path, viewport_matrix, *polygon_sink, min_feature_size_px);
+            delete vec;
+
+        } else if (name == "defs") {
+            /* ignore */
+        } else {
+            cerr << "  Unexpected child: <" << node.name() << ">" << endl;
+        }
+    }
+
+    cairo_restore(cr);
+}
+
+/* Export an SVG path element to gerber. Apply patterns and clip on the fly. */
+void gerbolyze::SVGDocument::export_svg_path(const RenderSettings &rset, const pugi::xml_node &node, Paths &clip_path) {
+    enum gerber_color fill_color = gerber_fill_color(node);
+    enum gerber_color stroke_color = gerber_stroke_color(node);
+
+    double stroke_width = usvg_double_attr(node, "stroke-width", /* default */ 1.0);
+    assert(stroke_width > 0.0);
+    enum ClipperLib::EndType end_type = clipper_end_type(node);
+    enum ClipperLib::JoinType join_type = clipper_join_type(node);
+    vector<double> dasharray;
+    parse_dasharray(node, dasharray);
+    /* TODO add stroke-miterlimit */
+
+    if (!fill_color && !stroke_color) { /* Ignore "transparent" paths */
+        return;
+    }
+
+    /* Load path from SVG path data and transform into document units. */
+    PolyTree ptree;
+    cairo_save(cr);
+    apply_cairo_transform_from_svg(cr, node.attribute("transform").value());
+    load_svg_path(cr, node, ptree);
+    cairo_restore (cr);
+
+    Paths open_paths, closed_paths;
+    OpenPathsFromPolyTree(ptree, open_paths);
+    ClosedPathsFromPolyTree(ptree, closed_paths);
+
+    /* Skip filling for transparent fills */
+    if (fill_color) {
+        /* Clip paths. Consider all paths closed for filling. */
+        if (!clip_path.empty()) {
+            Clipper c;
+            c.AddPaths(open_paths, ptSubject, /* closed */ false);
+            c.AddPaths(closed_paths, ptSubject, /* closed */ true);
+            c.AddPaths(clip_path, ptClip, /* closed */ true);
+            c.StrictlySimple(true);
+            /* fill rules are nonzero since both subject and clip have already been normalized by clipper. */ 
+            c.Execute(ctIntersection, ptree, pftNonZero, pftNonZero);
+        }
+
+        /* Call out to pattern tiler for pattern fills. The path becomes the clip here. */
+        if (fill_color == GRB_PATTERN_FILL) {
+            string fill_pattern_id = usvg_id_url(node.attribute("fill").value());
+            Pattern *pattern = lookup_pattern(fill_pattern_id);
+            if (!pattern) {
+                cerr << "Warning: Fill pattern with id \"" << fill_pattern_id << "\" not found." << endl;
+
+            } else {
+                Paths clip;
+                PolyTreeToPaths(ptree, clip);
+                pattern->tile(rset, clip);
+            }
+
+        } else { /* solid fill */
+            Paths f_polys;
+            /* Important for gerber spec compliance and also for reliable rendering results irrespective of board house
+             * and gerber viewer. */
+            dehole_polytree(ptree, f_polys);
+
+            /* Export SVG */
+            cairo_save(cr);
+            cairo_set_matrix(cr, &viewport_matrix);
+            cairo_new_path(cr);
+            ClipperLib::cairo::clipper_to_cairo(f_polys, cr, CAIRO_PRECISION, ClipperLib::cairo::tNone);
+            if (fill_color == GRB_DARK) {
+                cairo_set_source_rgba(cr, 0.0, 0.0, 1.0, dbg_fill_alpha);
+            } else { /* GRB_CLEAR */
+                cairo_set_source_rgba(cr, 1.0, 0.0, 0.0, dbg_fill_alpha);
+            }
+            cairo_fill (cr);
+
+            /* export gerber */
+            cairo_identity_matrix(cr);
+            for (const auto &poly : f_polys) {
+                vector<array<double, 2>> out;
+                for (const auto &p : poly)
+                    out.push_back(std::array<double, 2>{
+                            ((double)p.X) / clipper_scale, ((double)p.Y) / clipper_scale
+                            });
+                *polygon_sink << (fill_color == GRB_DARK ? GRB_POL_DARK : GRB_POL_CLEAR) << out;
+            }
+            cairo_restore(cr);
+        }
+    }
+
+    if (stroke_color && stroke_width > 0.0) {
+        ClipperOffset offx;
+        offx.ArcTolerance = 0.01 * clipper_scale; /* 10µm; TODO: Make this configurable */
+
+        /* For stroking we have to separately handle open and closed paths */
+        for (const auto &poly : closed_paths) {
+            if (poly.empty()) /* do we need this? */
+                continue;
+
+            /* Special case: A closed path becomes a number of open paths when it is dashed. */
+            if (dasharray.empty()) {
+                offx.AddPath(poly, join_type, etClosedLine);
+
+            } else {
+                Path poly_copy(poly);
+                poly_copy.push_back(poly[0]);
+                Paths out;
+                dash_path(poly_copy, out, dasharray);
+                offx.AddPaths(out, join_type, end_type);
+            }
+        }
+
+        for (const auto &poly : open_paths) {
+            Paths out;
+            dash_path(poly, out, dasharray);
+            offx.AddPaths(out, join_type, end_type);
+        }
+
+        /* Execute clipper offset operation to generate stroke outlines */
+        offx.Execute(ptree, 0.5 * stroke_width * clipper_scale);
+
+        /* Clip. Note that after the outline, all we have is closed paths as any open path's stroke outline is itself
+         * a closed path. */
+        if (!clip_path.empty()) {
+            Clipper c;
+
+            Paths outline_paths;
+            PolyTreeToPaths(ptree, outline_paths);
+            c.AddPaths(outline_paths, ptSubject, /* closed */ true);
+            c.AddPaths(clip_path, ptClip, /* closed */ true);
+            c.StrictlySimple(true);
+            /* fill rules are nonzero since both subject and clip have already been normalized by clipper. */ 
+            c.Execute(ctIntersection, ptree, pftNonZero, pftNonZero);
+        }
+
+        /* Call out to pattern tiler for pattern strokes. The stroke's outline becomes the clip here. */
+        if (stroke_color == GRB_PATTERN_FILL) {
+            string stroke_pattern_id = usvg_id_url(node.attribute("stroke").value());
+            Pattern *pattern = lookup_pattern(stroke_pattern_id);
+            if (!pattern) {
+                cerr << "Warning: Fill pattern with id \"" << stroke_pattern_id << "\" not found." << endl;
+
+            } else {
+                Paths clip;
+                PolyTreeToPaths(ptree, clip);
+                pattern->tile(rset, clip);
+            }
+
+        } else {
+            Paths s_polys;
+            dehole_polytree(ptree, s_polys);
+
+            /* Export debug svg */
+            cairo_save(cr);
+            cairo_set_matrix(cr, &viewport_matrix);
+            cairo_new_path(cr);
+            ClipperLib::cairo::clipper_to_cairo(s_polys, cr, CAIRO_PRECISION, ClipperLib::cairo::tNone);
+            if (stroke_color == GRB_DARK) {
+                cairo_set_source_rgba(cr, 0.0, 0.0, 1.0, dbg_stroke_alpha);
+            } else { /* GRB_CLEAR */
+                cairo_set_source_rgba(cr, 1.0, 0.0, 0.0, dbg_stroke_alpha);
+            }
+            cairo_fill (cr);
+
+            /* export gerber */
+            cairo_identity_matrix(cr);
+            for (const auto &poly : s_polys) {
+                vector<array<double, 2>> out;
+                for (const auto &p : poly)
+                    out.push_back(std::array<double, 2>{
+                            ((double)p.X) / clipper_scale, ((double)p.Y) / clipper_scale
+                            });
+                *polygon_sink << (stroke_color == GRB_DARK ? GRB_POL_DARK : GRB_POL_CLEAR) << out;
+            }
+            cairo_restore(cr);
+        }
+    }
+}
+
+void gerbolyze::SVGDocument::render(const RenderSettings &rset, PolygonSink &sink, const ElementSelector *sel) {
+    assert(_valid);
+    /* Export the actual SVG document to both SVG for debuggin and to gerber. We do this as we go, i.e. we immediately
+     * process each element to gerber as we encounter it instead of first rendering everything to a giant list of gerber
+     * primitives and then serializing those later. Exporting them on the fly saves a ton of memory and is much faster.
+     */
+    polygon_sink = &sink;
+    sink.header({vb_x, vb_y}, {vb_w, vb_h});
+    ClipperLib::Clipper c;
+    c.AddPaths(vb_paths, ptSubject, /* closed */ true);
+    ClipperLib::IntRect bbox = c.GetBounds();
+    cerr << "document viewbox clip: bbox={" << bbox.left << ", " << bbox.top << "} - {" << bbox.right << ", " << bbox.bottom << "}" << endl;
+    export_svg_group(rset, root_elem, vb_paths, sel, false, true);
+    sink.footer();
+}
+
+void gerbolyze::SVGDocument::render_to_list(const RenderSettings &rset, vector<pair<Polygon, GerberPolarityToken>> &out, const ElementSelector *sel) {
+    LambdaPolygonSink sink([&out](const Polygon &poly, GerberPolarityToken pol) {
+            out.emplace_back(pair<Polygon, GerberPolarityToken>{poly, pol});
+        });
+    render(rset, sink, sel);
+}
+
+void gerbolyze::SVGDocument::setup_debug_output(string filename) {
+    /* Setup cairo to draw into a SVG surface (for debugging). For actual rendering, something like a recording surface
+     * would work fine, too. */
+    /* Cairo expects the SVG surface size to be given in pt (72.0 pt = 1.0 in = 25.4 mm) */
+    const char *fn = filename.empty() ? nullptr : filename.c_str();
+    assert (!cr);
+    assert (!surface);
+    surface = cairo_svg_surface_create(fn, page_w_mm / 25.4 * 72.0, page_h_mm / 25.4 * 72.0);
+    cr = cairo_create (surface);
+    /* usvg returns "pixels", cairo thinks we draw "points" at 72.0 pt per inch. */
+    cairo_scale(cr, page_w / vb_w * 72.0 / assumed_usvg_dpi, page_h / vb_h * 72.0 / assumed_usvg_dpi);
+
+    cairo_translate(cr, -vb_x, -vb_y);
+
+    /* Store viewport transform and reset cairo's active transform. We have to do this since we have to render out all
+     * gerber primitives in mm, not px and most gerber primitives we export pass through Cairo at some point.
+     *
+     * We manually apply this viewport transform every time for debugging we actually use Cairo to export SVG. */
+    cairo_get_matrix(cr, &viewport_matrix);
+    cairo_identity_matrix(cr);
+
+    cairo_set_line_width (cr, 0.1);
+    cairo_set_source_rgba (cr, 1.0, 0.0, 0.0, 1.0);
+}
+
+void gerbolyze::SVGDocument::setup_viewport_clip() {
+    /* Set up view port clip path */
+    Path vb_path;
+    for (auto &elem : vector<pair<double, double>> {{vb_x, vb_y}, {vb_x+vb_w, vb_y}, {vb_x+vb_w, vb_y+vb_h}, {vb_x, vb_y+vb_h}}) {
+        double x = elem.first, y = elem.second;
+        vb_path.push_back({ (cInt)round(x * clipper_scale), (cInt)round(y * clipper_scale) });
+    }
+    vb_paths.push_back(vb_path);
+
+    ClipperLib::Clipper c;
+    c.AddPaths(vb_paths, ptSubject, /* closed */ true);
+}
+
+void gerbolyze::SVGDocument::load_patterns() {
+    /* Set up document-wide pattern registry. Load patterns from <defs> node. */
+    for (const auto &node : defs_node.children("pattern")) {
+        pattern_map.emplace(std::piecewise_construct, std::forward_as_tuple(node.attribute("id").value()), std::forward_as_tuple(node, *this));
+    }
+}
+
+void gerbolyze::SVGDocument::load_clips() {
+    /* Set up document-wide clip path registry: Extract clip path definitions from <defs> element */
+    for (const auto &node : defs_node.children("clipPath")) {
+        cairo_save(cr);
+        apply_cairo_transform_from_svg(cr, node.attribute("transform").value());
+
+        string meta_clip_path_id(usvg_id_url(node.attribute("clip-path").value()));
+        Clipper c;
+
+        /* The clipPath node can only contain <path> children. usvg converts all geometric objects (rect etc.) to
+         * <path>s. Raster images are invalid inside a clip path. usvg removes all groups that are not relevant to
+         * rendering, and the only way a group might stay is if it affects rasterization (e.g. through mask, clipPath).
+         */
+        for (const auto &child : node.children("path")) {
+            PolyTree ptree;
+            cairo_save(cr);
+            /* TODO: we currently only support clipPathUnits="userSpaceOnUse", not "objectBoundingBox". */
+            apply_cairo_transform_from_svg(cr, child.attribute("transform").value());
+            load_svg_path(cr, child, ptree);
+            cairo_restore (cr);
+
+            Paths paths;
+            PolyTreeToPaths(ptree, paths);
+            c.AddPaths(paths, ptSubject, /* closed */ false);
+        }
+
+        /* Support clip paths that themselves have clip paths */
+        if (!meta_clip_path_id.empty()) {
+            if (clip_path_map.contains(meta_clip_path_id)) {
+                /* all clip paths must be closed */
+                c.AddPaths(clip_path_map[meta_clip_path_id], ptClip, /* closed */ true);
+
+            } else {
+                cerr << "Warning: Cannot find clip path with ID \"" << meta_clip_path_id << "\", ignoring." << endl;
+            }
+        }
+
+        PolyTree ptree;
+        c.StrictlySimple(true);
+        /* This unions all child <path>s together and at the same time applies any meta clip path. */
+        /* The fill rules are both nonzero since both subject and clip have already been normalized by clipper. */ 
+        c.Execute(ctUnion, ptree, pftNonZero, pftNonZero);
+        /* Insert into document clip path map */
+        PolyTreeToPaths(ptree, clip_path_map[node.attribute("id").value()]);
+
+        cairo_restore(cr);
+    }
+}
+
+/* Note: These values come from KiCAD's common/lset.cpp. KiCAD uses *multiple different names* for the same layer in
+ * different places, and not all of them are stable. Sometimes, these names change without notice. If this list isn't
+ * up-to-date, it's not my fault. Still, please file an issue. */
+const std::vector<std::string> gerbolyze::kicad_default_layers ({
+        /* Copper */
+        "F.Cu",
+        "In1.Cu", "In2.Cu", "In3.Cu", "In4.Cu", "In5.Cu", "In6.Cu", "In7.Cu", "In8.Cu",
+        "In9.Cu", "In10.Cu", "In11.Cu", "In12.Cu", "In13.Cu", "In14.Cu", "In15.Cu", "In16.Cu",
+        "In17.Cu", "In18.Cu", "In19.Cu", "In20.Cu", "In21.Cu", "In22.Cu", "In23.Cu",
+        "In24.Cu", "In25.Cu", "In26.Cu", "In27.Cu", "In28.Cu", "In29.Cu", "In30.Cu",
+        "B.Cu",
+
+        /* Technical layers */
+        "B.Adhes", "F.Adhes",
+        "B.Paste", "F.Paste",
+        "B.SilkS", "F.SilkS",
+        "B.Mask", "F.Mask",
+
+        /* User layers */
+        "Dwgs.User",
+        "Cmts.User",
+        "Eco1.User", "Eco2.User",
+        "Edge.Cuts",
+        "Margin",
+
+        /* Footprint layers */
+        "F.CrtYd", "B.CrtYd",
+        "F.Fab", "B.Fab",
+
+        /* Layers for user scripting etc. */
+        "User.1", "User.2", "User.3", "User.4", "User.5", "User.6", "User.7", "User.8", "User.9",
+        });
diff --git a/svg-flatten/src/svg_geom.cpp b/svg-flatten/src/svg_geom.cpp
new file mode 100644
index 0000000..385e848
--- /dev/null
+++ b/svg-flatten/src/svg_geom.cpp
@@ -0,0 +1,182 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "svg_geom.h"
+
+#include <cmath>
+#include <string>
+#include <sstream>
+#include <queue>
+#include <assert.h>
+#include <cairo.h>
+#include "svg_import_defs.h"
+
+using namespace ClipperLib;
+using namespace std;
+
+/* Get bounding box of a Clipper Paths */
+IntRect gerbolyze::get_paths_bounds(const Paths &paths) {
+    if (paths.empty()) {
+        return {0, 0, 0, 0};
+    }
+
+    if (paths[0].empty()) {
+        return {0, 0, 0, 0};
+    }
+
+    IntPoint p0 = paths[0][0];
+    cInt x0=p0.X, y0=p0.Y, x1=p0.X, y1=p0.Y;
+
+    for (const Path &p : paths) {
+        for (const IntPoint ip : p) {
+            if (ip.X < x0)
+                x0 = ip.X;
+
+            if (ip.Y < y0)
+                y0 = ip.Y;
+
+            if (ip.X > x1)
+                x1 = ip.X;
+
+            if (ip.Y > y1)
+                y1 = ip.Y;
+        }
+    }
+
+    return {x0, y0, x1, y1};
+}
+
+enum ClipperLib::PolyFillType gerbolyze::clipper_fill_rule(const pugi::xml_node &node) {
+    string val(node.attribute("fill-rule").value());
+    if (val == "evenodd")
+        return ClipperLib::pftEvenOdd;
+    else
+        return ClipperLib::pftNonZero; /* default */
+}
+
+enum ClipperLib::EndType gerbolyze::clipper_end_type(const pugi::xml_node &node) {
+    string val(node.attribute("stroke-linecap").value());
+    if (val == "round")
+        return ClipperLib::etOpenRound;
+
+    if (val == "square")
+        return ClipperLib::etOpenSquare;
+
+    return ClipperLib::etOpenButt;
+}
+
+enum ClipperLib::JoinType gerbolyze::clipper_join_type(const pugi::xml_node &node) {
+    string val(node.attribute("stroke-linejoin").value());
+    if (val == "round")
+        return ClipperLib::jtRound;
+
+    if (val == "bevel")
+        return ClipperLib::jtSquare;
+
+    return ClipperLib::jtMiter;
+}
+
+static void dehole_polytree_worker(PolyNode &ptree, Paths &out, queue<PolyTree> &todo) {
+    for (int i=0; i<ptree.ChildCount(); i++) {
+        PolyNode *nod = ptree.Childs[i];
+        assert(nod);
+        assert(!nod->IsHole());
+
+        /* First, recursively process inner polygons. */
+        for (int j=0; j<nod->ChildCount(); j++) {
+            PolyNode *child = nod->Childs[j];
+            assert(child);
+            assert(child->IsHole());
+
+            if (child->ChildCount() > 0) {
+                dehole_polytree_worker(*child, out, todo);
+            }
+        }
+
+        if (nod->ChildCount() == 0) {
+            out.push_back(nod->Contour);
+
+        } else {
+
+            /* Do not add children's children, those were handled in the recursive call above */
+            Clipper c;
+            c.AddPath(nod->Contour, ptSubject, /* closed= */ true);
+            for (int k=0; k<nod->ChildCount(); k++) {
+                c.AddPath(nod->Childs[k]->Contour, ptSubject, /* closed= */ true);
+            }
+
+            /* Find a viable cut: Cut from top-left bounding box corner, through two subsequent points on the hole
+             * outline and to top-right bbox corner. */
+            IntRect bbox = c.GetBounds();
+            Path tri = { { bbox.left, bbox.top }, nod->Childs[0]->Contour[0], nod->Childs[0]->Contour[1], { bbox.right, bbox.top } };
+            c.AddPath(tri, ptClip, true);
+
+            c.StrictlySimple(true);
+            /* Execute twice, once for intersection fragment and once for difference fragment. Note that this will yield
+             * at least two, but possibly more polygons. */
+            c.Execute(ctDifference, todo.emplace(), pftNonZero);
+            c.Execute(ctIntersection, todo.emplace(), pftNonZero);
+        }
+    }
+}
+
+/* Take a Clipper polytree, i.e. a description of a set of polygons, their holes and their inner polygons, and remove
+ * all holes from it. We remove holes by splitting each polygon that has a hole into two or more pieces so that the hole
+ * is no more. These pieces perfectly fit each other so there is no visual or functional difference.
+ */
+void gerbolyze::dehole_polytree(PolyTree &ptree, Paths &out) {
+    queue<PolyTree> todo;
+    dehole_polytree_worker(ptree, out, todo);
+    while (!todo.empty()) {
+        dehole_polytree_worker(todo.front(), out, todo);
+        todo.pop();
+    }
+}
+
+
+/* Intersect two clip paths. Both must share a coordinate system. */
+void gerbolyze::combine_clip_paths(Paths &in_a, Paths &in_b, Paths &out) {
+    Clipper c;
+    c.StrictlySimple(true);
+    c.AddPaths(in_a, ptClip, /* closed */ true);
+    c.AddPaths(in_b, ptSubject, /* closed */ true);
+    /* Nonzero fill since both input clip paths must already have been preprocessed by clipper. */
+    c.Execute(ctIntersection, out, pftNonZero);
+}
+
+/* Transform given clipper paths under the given cairo transform. If no transform is given, use cairo's current
+ * user-to-device transform. */
+void gerbolyze::transform_paths(cairo_t *cr, Paths &paths, cairo_matrix_t *mat) {
+    cairo_save(cr);
+    if (mat != nullptr) {
+        cairo_set_matrix(cr, mat);
+    }
+    
+    for (Path &p : paths) {
+        transform(p.begin(), p.end(), p.begin(),
+                [cr](IntPoint p) -> IntPoint {
+                    double x = p.X / clipper_scale, y = p.Y / clipper_scale;
+                    cairo_user_to_device(cr, &x, &y);
+                    return { (cInt)round(x * clipper_scale), (cInt)round(y * clipper_scale) };
+                });
+    }
+
+    cairo_restore(cr);
+}
+
+
diff --git a/svg-flatten/src/svg_geom.h b/svg-flatten/src/svg_geom.h
new file mode 100644
index 0000000..5f00479
--- /dev/null
+++ b/svg-flatten/src/svg_geom.h
@@ -0,0 +1,36 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <cairo.h>
+#include <clipper.hpp>
+#include <pugixml.hpp>
+
+namespace gerbolyze {
+
+ClipperLib::IntRect get_paths_bounds(const ClipperLib::Paths &paths);
+enum ClipperLib::PolyFillType clipper_fill_rule(const pugi::xml_node &node);
+enum ClipperLib::EndType clipper_end_type(const pugi::xml_node &node);
+enum ClipperLib::JoinType clipper_join_type(const pugi::xml_node &node);
+void dehole_polytree(ClipperLib::PolyTree &ptree, ClipperLib::Paths &out);
+void combine_clip_paths(ClipperLib::Paths &in_a, ClipperLib::Paths &in_b, ClipperLib::Paths &out);
+void transform_paths(cairo_t *cr, ClipperLib::Paths &paths, cairo_matrix_t *mat=nullptr);
+
+} /* namespace gerbolyze */
+
diff --git a/svg-flatten/src/svg_import_defs.h b/svg-flatten/src/svg_import_defs.h
new file mode 100644
index 0000000..e25c52c
--- /dev/null
+++ b/svg-flatten/src/svg_import_defs.h
@@ -0,0 +1,49 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2016 CERN
+ * @author Janito V. Ferreira Filho <janito.vff@gmail.com>
+ * Copyright (C) 2018-2019 KiCad Developers, see AUTHORS.txt for contributors.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you may find one here:
+ * http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+ * or you may search the http://www.gnu.org website for the version 2 license,
+ * or you may write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
+ */
+
+#ifndef SVG_IMPORT_DEFS_H
+#define SVG_IMPORT_DEFS_H
+
+#include <cfloat>
+
+template <typename T>
+constexpr T ipow(T num, unsigned int pow)
+{
+    return (pow >= sizeof(unsigned int)*8) ? 0 :
+        pow == 0 ? 1 : num * ipow(num, pow-1);
+}
+
+constexpr int CAIRO_PRECISION = 7;
+constexpr double clipper_scale = ipow(10.0, CAIRO_PRECISION);
+
+#define JC_VORONOI_IMPLEMENTATION
+#define JCV_REAL_TYPE double
+#define JCV_ATAN2 atan2
+#define JCV_SQRT sqrt
+#define JCV_FLT_MAX DBL_MAX
+#define JCV_PI 3.141592653589793115997963468544185161590576171875
+//define JCV_EDGE_INTERSECT_THRESHOLD 1.0e-10F
+
+#endif /* SVG_IMPORT_DEFS_H */
diff --git a/svg-flatten/src/svg_import_util.cpp b/svg-flatten/src/svg_import_util.cpp
new file mode 100644
index 0000000..efa7701
--- /dev/null
+++ b/svg-flatten/src/svg_import_util.cpp
@@ -0,0 +1,123 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <cmath>
+#include "base64.h"
+#include "svg_import_util.h"
+
+using namespace std;
+
+void gerbolyze::print_matrix(cairo_t *cr, bool print_examples) {
+    cairo_matrix_t mat;
+    cairo_get_matrix(cr, &mat);
+    cerr << "    xform matrix = { xx=" << mat.xx << ", yx=" << mat.yx << ", xy=" << mat.xy << ", yy=" << mat.yy << ", x0=" << mat.x0 << ", y0=" << mat.y0 << " }" << endl;
+    if (print_examples) {
+        double x=0, y=0;
+        cairo_user_to_device(cr, &x, &y);
+        cerr << "        (0, 0) -> (" << x << ", " << y << ")" << endl;
+        x = 1, y = 0;
+        cairo_user_to_device(cr, &x, &y);
+        cerr << "        (1, 0) -> (" << x << ", " << y << ")" << endl;
+        x = 0, y = 1;
+        cairo_user_to_device(cr, &x, &y);
+        cerr << "        (0, 1) -> (" << x << ", " << y << ")" << endl;
+        x = 1, y = 1;
+        cairo_user_to_device(cr, &x, &y);
+        cerr << "        (1, 1) -> (" << x << ", " << y << ")" << endl;
+    }
+}
+
+/* Read a double value formatted like usvg formats doubles from an SVG attribute */
+double gerbolyze::usvg_double_attr(const pugi::xml_node &node, const char *attr, double default_value) {
+    const auto *val = node.attribute(attr).value();
+    if (*val == '\0')
+        return default_value;
+
+    return atof(val);
+}
+
+/* Read an url from an usvg attribute */
+string gerbolyze::usvg_id_url(string attr) {
+    if (attr.rfind("url(#", 0) == string::npos)
+        return string();
+
+    attr = attr.substr(strlen("url(#"));
+    attr = attr.substr(0, attr.size()-1);
+    return attr;
+}
+
+gerbolyze::RelativeUnits gerbolyze::map_str_to_units(string str, gerbolyze::RelativeUnits default_val) {
+    if (str == "objectBoundingBox")
+        return SVG_ObjectBoundingBox;
+    else if (str == "userSpaceOnUse")
+        return SVG_UserSpaceOnUse;
+    return default_val;
+}
+
+void gerbolyze::load_cairo_matrix_from_svg(const string &transform, cairo_matrix_t &mat) {
+    if (transform.empty()) {
+        cairo_matrix_init_identity(&mat);
+        return;
+    }
+
+    string start("matrix(");
+    assert(transform.substr(0, start.length()) == start);
+    assert(transform.back() == ')');
+    const string &foo = transform.substr(start.length(), transform.length());
+    const string &bar = foo.substr(0, foo.length() - 1);
+
+    istringstream xform(bar);
+
+    double a, c, e,
+           b, d, f;
+    xform >> a >> b >> c >> d >> e >> f;
+    assert(!xform.fail());
+
+    cairo_matrix_init(&mat, a, b, c, d, e, f);
+}
+
+void gerbolyze::apply_cairo_transform_from_svg(cairo_t *cr, const string &transform) {
+    cairo_matrix_t mat;
+    load_cairo_matrix_from_svg(transform, mat);
+    cairo_transform(cr, &mat); /* or cairo_transform? */
+}
+
+/* Cf. https://tools.ietf.org/html/rfc2397 */
+string gerbolyze::parse_data_iri(const string &data_url) {
+    if (data_url.rfind("data:", 0) == string::npos) /* check if url starts with "data:" */
+        return string();
+
+    size_t foo = data_url.find("base64,");
+    if (foo == string::npos) /* check if this is actually a data URL */
+        return string();
+
+    size_t b64_begin = data_url.find_first_not_of(" ", foo + strlen("base64,"));
+    assert(b64_begin != string::npos);
+
+    return base64_decode(data_url.substr(b64_begin));
+}
+
+/* for debug svg output */
+void gerbolyze::apply_viewport_matrix(cairo_t *cr, cairo_matrix_t &viewport_matrix) {
+    /* Multiply viewport matrix *from the left*, i.e. as if it had been applied *before* the currently set matrix. */
+    cairo_matrix_t old_matrix;
+    cairo_get_matrix(cr, &old_matrix);
+    cairo_set_matrix(cr, &viewport_matrix);
+    cairo_transform(cr, &old_matrix);
+}
+
diff --git a/svg-flatten/src/svg_import_util.h b/svg-flatten/src/svg_import_util.h
new file mode 100644
index 0000000..a6cd2d6
--- /dev/null
+++ b/svg-flatten/src/svg_import_util.h
@@ -0,0 +1,61 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <math.h>
+#include <cmath>
+#include <stdlib.h>
+#include <assert.h>
+#include <limits>
+#include <vector>
+#include <string>
+#include <iostream>
+#include <sstream>
+#include <regex>
+
+#include <pango/pangocairo.h>
+#include <cairo-svg.h>
+
+#include <clipper.hpp>
+#include "cairo_clipper.hpp"
+
+#include <pugixml.hpp>
+
+#include "svg_import_defs.h"
+
+namespace gerbolyze {
+
+/* Coordinate system selection for things like "patternContentUnits" */
+enum RelativeUnits {
+    SVG_UnknownUnits = 0,
+    SVG_UserSpaceOnUse,
+    SVG_ObjectBoundingBox,
+};
+
+void print_matrix(cairo_t *cr, bool print_examples=false);
+double usvg_double_attr(const pugi::xml_node &node, const char *attr, double default_value=0.0);
+std::string usvg_id_url(std::string attr);
+RelativeUnits map_str_to_units(std::string str, RelativeUnits default_val=SVG_UnknownUnits);
+void load_cairo_matrix_from_svg(const std::string &transform, cairo_matrix_t &mat);
+void apply_cairo_transform_from_svg(cairo_t *cr, const std::string &transform);
+std::string parse_data_iri(const std::string &data_url);
+void apply_viewport_matrix(cairo_t *cr, cairo_matrix_t &viewport_matrix);
+
+} /* namespace gerbolyze */
+
diff --git a/svg-flatten/src/svg_path.cpp b/svg-flatten/src/svg_path.cpp
new file mode 100644
index 0000000..537b5dd
--- /dev/null
+++ b/svg-flatten/src/svg_path.cpp
@@ -0,0 +1,213 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <cmath>
+#include <assert.h>
+#include <iostream>
+#include <sstream>
+#include "cairo_clipper.hpp"
+#include "svg_import_defs.h"
+#include "svg_path.h"
+
+using namespace std;
+
+static void clipper_add_cairo_path(cairo_t *cr, ClipperLib::Clipper &c, bool closed) {
+    ClipperLib::Paths in_poly;
+    ClipperLib::cairo::cairo_to_clipper(cr, in_poly, CAIRO_PRECISION, ClipperLib::cairo::tNone);
+    c.AddPaths(in_poly, ClipperLib::ptSubject, closed);
+}
+
+static void path_to_clipper_via_cairo(cairo_t *cr, ClipperLib::Clipper &c, const pugi::char_t *path_data) {
+    istringstream d(path_data);
+
+    string cmd;
+    double x, y, c1x, c1y, c2x, c2y;
+
+    bool first = true;
+    bool path_is_empty = true;
+    while (!d.eof()) {
+        d >> cmd;
+        assert (!d.fail());
+        assert(!first || cmd == "M");
+        
+        if (cmd == "Z") { /* Close path */
+            cairo_close_path(cr);
+            clipper_add_cairo_path(cr, c, /* closed= */ true);
+            cairo_new_path(cr);
+            path_is_empty = true;
+
+        } else if (cmd == "M") { /* Move to */
+            d >> x >> y;
+            /* We need to transform all points ourselves here, and cannot use the transform feature of cairo_to_clipper:
+             * Our transform may contain offsets, and clipper only passes its data into cairo's transform functions
+             * after scaling up to its internal fixed-point ints, but it does not scale the transform accordingly. This
+             * means a scale/rotation we set before calling clipper works out fine, but translations get lost as they
+             * get scaled by something like 1e-6.
+             */
+            cairo_user_to_device(cr, &x, &y);
+            assert (!d.fail());
+            if (!first)
+                clipper_add_cairo_path(cr, c, /* closed= */ false);
+            cairo_new_path (cr);
+            path_is_empty = true;
+            cairo_move_to(cr, x, y);
+
+        } else if (cmd == "L") { /* Line to */
+            d >> x >> y;
+            cairo_user_to_device(cr, &x, &y);
+            assert (!d.fail());
+            cairo_line_to(cr, x, y);
+            path_is_empty = false;
+
+        } else { /* Curve to */
+            assert(cmd == "C");
+            d >> c1x >> c1y; /* first control point */
+            cairo_user_to_device(cr, &c1x, &c1y);
+            d >> c2x >> c2y; /* second control point */
+            cairo_user_to_device(cr, &c2x, &c2y);
+            d >> x >> y; /* end point */
+            cairo_user_to_device(cr, &x, &y);
+            assert (!d.fail());
+            cairo_curve_to(cr, c1x, c1y, c2x, c2y, x, y);
+            path_is_empty = false;
+        }
+
+        first = false;
+    }
+    if (!path_is_empty) {
+        cairo_close_path(cr);
+        clipper_add_cairo_path(cr, c, /* closed= */ false);
+    }
+}
+
+void gerbolyze::load_svg_path(cairo_t *cr, const pugi::xml_node &node, ClipperLib::PolyTree &ptree) {
+    auto *path_data = node.attribute("d").value();
+    auto fill_rule = clipper_fill_rule(node);
+
+    /* For open paths, clipper does not correctly remove self-intersections. Thus, we pass everything into
+     * clipper twice: Once with all paths set to "closed" to compute fill areas, and once with correct
+     * open/closed properties for stroke offsetting. */
+    cairo_set_tolerance (cr, 0.1); /* FIXME make configurable, scale properly for units */
+    cairo_set_fill_rule(cr, CAIRO_FILL_RULE_WINDING);
+
+    ClipperLib::Clipper c;
+    c.StrictlySimple(true);
+    path_to_clipper_via_cairo(cr, c, path_data);
+    /* We canont clip the polygon here since that would produce incorrect results for our stroke. */
+    c.Execute(ClipperLib::ctUnion, ptree, fill_rule, ClipperLib::pftNonZero);
+}
+
+void gerbolyze::parse_dasharray(const pugi::xml_node &node, vector<double> &out) {
+    out.clear();
+
+    string val(node.attribute("stroke-dasharray").value());
+    if (val.empty() || val == "none")
+        return;
+
+    istringstream desc_stream(val);
+    while (!desc_stream.eof()) {
+        /* usvg says the array only contains unitless (px) values. I don't know what resvg does with percentages inside
+         * dash arrays. We just assume everything is a unitless number here. In case usvg passes through percentages,
+         * well, bad luck. They are a kind of weird thing inside a dash array in the first place. */ 
+        double d;
+        desc_stream >> d;
+        out.push_back(d);
+    }
+
+    assert(out.size() % 2 == 0); /* according to resvg spec */
+}
+
+/* Take a Clipper path in clipper-scaled document units, and apply the given SVG dash array to it. Do this by walking
+ * the path from start to end while emitting dashes. */
+void gerbolyze::dash_path(const ClipperLib::Path &in, ClipperLib::Paths &out, const vector<double> dasharray, double dash_offset) {
+    out.clear();
+    if (dasharray.empty() || in.size() < 2) {
+        out.push_back(in);
+        return;
+    }
+
+    size_t dash_idx = 0;
+    size_t num_dashes = dasharray.size();
+    while (dash_offset > dasharray[dash_idx]) {
+        dash_offset -= dasharray[dash_idx];
+        dash_idx = (dash_idx + 1) % num_dashes;
+    }
+
+    double dash_remaining = dasharray[dash_idx] - dash_offset;
+
+    ClipperLib::Path current_dash;
+    current_dash.push_back(in[0]);
+    double dbg_total_len = 0.0;
+    for (size_t i=1; i<in.size(); i++) {
+        ClipperLib::IntPoint p1(in[i-1]), p2(in[i]);
+
+        double x1 = p1.X / clipper_scale, y1 = p1.Y / clipper_scale, x2 = p2.X / clipper_scale, y2 = p2.Y / clipper_scale;
+        double dist = sqrt(pow(x2-x1, 2) + pow(y2-y1, 2));
+        dbg_total_len += dist;
+
+        if (dist < dash_remaining) {
+            /* dash extends beyond this segment, append this segment and continue. */
+            dash_remaining -= dist;
+            current_dash.push_back(p2);
+
+        } else {
+            /* dash started in some previous segment ends in this segment */
+            double dash_frac = dash_remaining/dist;
+            double x = x1 + (x2 - x1) * dash_frac,
+                   y = y1 + (y2 - y1) * dash_frac;
+            ClipperLib::IntPoint intermediate {(ClipperLib::cInt)round(x * clipper_scale), (ClipperLib::cInt)round(y * clipper_scale)};
+
+            /* end this dash */
+            current_dash.push_back(intermediate);
+            if (dash_idx%2 == 0) { /* dash */
+                out.push_back(current_dash);
+            } /* else space */
+            dash_idx = (dash_idx + 1) % num_dashes;
+            double offset = dash_remaining;
+
+            /* start next dash */
+            current_dash.clear();
+            current_dash.push_back(intermediate);
+
+            /* handle case where multiple dashes fit into this segment */
+            while ((dist - offset) > dasharray[dash_idx]) {
+                offset += dasharray[dash_idx];
+
+                double dash_frac = offset/dist;
+                double x = x1 + (x2 - x1) * dash_frac,
+                       y = y1 + (y2 - y1) * dash_frac;
+                ClipperLib::IntPoint intermediate {(ClipperLib::cInt)round(x * clipper_scale), (ClipperLib::cInt)round(y * clipper_scale)};
+
+                /* end this dash */
+                current_dash.push_back(intermediate);
+                if (dash_idx%2 == 0) { /* dash */
+                    out.push_back(current_dash);
+                } /* else space */
+                dash_idx = (dash_idx + 1) % num_dashes;
+
+                /* start next dash */
+                current_dash.clear();
+                current_dash.push_back(intermediate);
+            }
+
+            dash_remaining = dasharray[dash_idx] - (dist - offset);
+            current_dash.push_back(p2);
+        }
+    }
+}
+
diff --git a/svg-flatten/src/svg_path.h b/svg-flatten/src/svg_path.h
new file mode 100644
index 0000000..9c65fdd
--- /dev/null
+++ b/svg-flatten/src/svg_path.h
@@ -0,0 +1,30 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <vector>
+#include <cairo.h>
+#include "svg_geom.h"
+
+namespace gerbolyze {
+void load_svg_path(cairo_t *cr, const pugi::xml_node &node, ClipperLib::PolyTree &ptree);
+void parse_dasharray(const pugi::xml_node &node, std::vector<double> &out);
+void dash_path(const ClipperLib::Path &in, ClipperLib::Paths &out, const std::vector<double> dasharray, double dash_offset=0.0);
+}
+
diff --git a/svg-flatten/src/svg_pattern.cpp b/svg-flatten/src/svg_pattern.cpp
new file mode 100644
index 0000000..b62df28
--- /dev/null
+++ b/svg-flatten/src/svg_pattern.cpp
@@ -0,0 +1,113 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <assert.h>
+#include "svg_import_util.h"
+#include "svg_pattern.h"
+#include "svg_import_defs.h"
+#include "svg_geom.h"
+#include <gerbolyze.hpp>
+
+using namespace std;
+
+gerbolyze::Pattern::Pattern(const pugi::xml_node &node, SVGDocument &doc) : _node(node), doc(&doc) {
+    /* Read pattern attributes from SVG node */
+    cerr << "creating pattern for node with id \"" << node.attribute("id").value() << "\"" << endl;
+    x = usvg_double_attr(node, "x");
+    y = usvg_double_attr(node, "y");
+    w = usvg_double_attr(node, "width");
+    h = usvg_double_attr(node, "height");
+    patternTransform = node.attribute("patternTransform").value();
+
+    string vb_s(node.attribute("viewBox").value());
+    has_vb = !vb_s.empty();
+    if (has_vb) {
+        istringstream vb_stream(vb_s);
+        vb_stream >> vb_x >> vb_y >> vb_w >> vb_h;
+    }
+
+    patternUnits = map_str_to_units(node.attribute("patternUnits").value(), SVG_ObjectBoundingBox);
+    patternContentUnits = map_str_to_units(node.attribute("patternContentUnits").value(), SVG_UserSpaceOnUse);
+}
+
+/* Tile pattern into gerber. Note that this function may be called several times in case the pattern is
+ * referenced from multiple places, so we must not clobber any of the object's state. */
+void gerbolyze::Pattern::tile (const gerbolyze::RenderSettings &rset, ClipperLib::Paths &clip) {
+    assert(doc);
+    cairo_t *cr = doc->cairo();
+    assert(cr);
+
+    cairo_save(cr);
+    /* Transform x, y, w, h from pattern coordinate space into parent coordinates by applying the inverse
+     * patternTransform. This is necessary so we iterate over the correct bounds when tiling below */
+    cairo_matrix_t mat;
+    load_cairo_matrix_from_svg(patternTransform, mat);
+    if (cairo_matrix_invert(&mat) != CAIRO_STATUS_SUCCESS) {
+        cerr << "Cannot invert patternTransform matrix on pattern \"" << _node.attribute("id").value() << "\"." << endl;
+        cairo_restore(cr);
+    }
+    double inst_x = x, inst_y = y, inst_w = w, inst_h = h;
+    cairo_user_to_device(cr, &inst_x, &inst_y);
+    cairo_user_to_device_distance(cr, &inst_w, &inst_h);
+    cairo_restore(cr);
+
+    ClipperLib::IntRect clip_bounds = get_paths_bounds(clip);
+    double bx = clip_bounds.left / clipper_scale;
+    double by = clip_bounds.top / clipper_scale;
+    double bw = (clip_bounds.right - clip_bounds.left) / clipper_scale;
+    double bh = (clip_bounds.bottom - clip_bounds.top) / clipper_scale;
+
+    if (patternUnits == SVG_ObjectBoundingBox) {
+        inst_x *= bw;
+        inst_y *= bh;
+        inst_w *= bw;
+        inst_h *= bh;
+    }
+
+    /* Switch to pattern coordinates */
+    cairo_save(cr);
+    cairo_translate(cr, bx, by);
+    apply_cairo_transform_from_svg(cr, patternTransform);
+
+    /* Iterate over all pattern tiles in pattern coordinates */
+    for (double inst_off_x = fmod(inst_x, inst_w) - inst_w;
+            inst_off_x < bw + inst_w;
+            inst_off_x += inst_w) {
+
+        for (double inst_off_y = fmod(inst_y, inst_h) - inst_h;
+                inst_off_y < bh + inst_h;
+                inst_off_y += inst_h) {
+
+            cairo_save(cr);
+            /* Change into this individual tile's coordinate system */
+            cairo_translate(cr, inst_off_x, inst_off_y);
+            if (has_vb) {
+                cairo_translate(cr, vb_x, vb_y);
+                cairo_scale(cr, inst_w / vb_w, inst_h / vb_h);
+            } else if (patternContentUnits == SVG_ObjectBoundingBox) {
+                cairo_scale(cr, bw, bh);
+            }
+
+            /* Export the pattern tile's content like a group */
+            doc->export_svg_group(rset, _node, clip);
+            cairo_restore(cr);
+        }
+    }
+    cairo_restore(cr);
+}
+
diff --git a/svg-flatten/src/svg_pattern.h b/svg-flatten/src/svg_pattern.h
new file mode 100644
index 0000000..e6a6fe2
--- /dev/null
+++ b/svg-flatten/src/svg_pattern.h
@@ -0,0 +1,51 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <string>
+#include <cairo.h>
+#include <pugixml.hpp>
+#include <clipper.hpp>
+#include "svg_import_util.h"
+
+namespace gerbolyze {
+
+class SVGDocument;
+class RenderSettings;
+
+class Pattern {
+public:
+    Pattern() {}
+    Pattern(const pugi::xml_node &node, SVGDocument &doc);
+
+    void tile (const gerbolyze::RenderSettings &rset, ClipperLib::Paths &clip);
+
+private:
+    double x, y, w, h;
+    double vb_x, vb_y, vb_w, vb_h;
+    bool has_vb;
+    std::string patternTransform;
+    enum RelativeUnits patternUnits;
+    enum RelativeUnits patternContentUnits;
+    const pugi::xml_node _node;
+    SVGDocument *doc = nullptr;
+};
+
+} /* namespace gerbolyze */
+
diff --git a/svg-flatten/src/vec_core.cpp b/svg-flatten/src/vec_core.cpp
new file mode 100644
index 0000000..9d2909f
--- /dev/null
+++ b/svg-flatten/src/vec_core.cpp
@@ -0,0 +1,567 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <cmath>
+#include <string>
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include <regex>
+#include <opencv2/opencv.hpp>
+#include "svg_import_util.h"
+#include "vec_core.h"
+#include "svg_import_defs.h"
+#include "jc_voronoi.h"
+
+using namespace gerbolyze;
+using namespace std;
+
+ImageVectorizer *gerbolyze::makeVectorizer(const std::string &name) {
+    if (name == "poisson-disc")
+        return new VoronoiVectorizer(POISSON_DISC, /* relax */ true);
+    else if (name == "hex-grid")
+        return new VoronoiVectorizer(HEXGRID, /* relax */ false);
+    else if (name == "square-grid")
+        return new VoronoiVectorizer(SQUAREGRID, /* relax */ false);
+    else if (name == "binary-contours")
+        return new OpenCVContoursVectorizer();
+    else if (name == "dev-null")
+        return new DevNullVectorizer();
+
+    return nullptr;
+}
+
+/* debug function */
+static void dbg_show_cv_image(cv::Mat &img) {
+    string windowName = "Debug image";
+    cv::namedWindow(windowName);
+    cv::imshow(windowName, img);
+    cv::waitKey(0);
+    cv::destroyWindow(windowName);
+}
+
+/* From jcv voronoi README */
+static void voronoi_relax_points(const jcv_diagram* diagram, jcv_point* points) {
+    const jcv_site* sites = jcv_diagram_get_sites(diagram);
+    for (int i=0; i<diagram->numsites; i++) {
+        const jcv_site* site = &sites[i];
+        jcv_point sum = site->p;
+        int count = 1;
+
+        const jcv_graphedge* edge = site->edges;
+
+        while (edge) {
+            sum.x += edge->pos[0].x;
+            sum.y += edge->pos[0].y;
+            count++;
+            edge = edge->next;
+        }
+
+        points[site->index].x = sum.x / count;
+        points[site->index].y = sum.y / count;
+    }
+} 
+
+void gerbolyze::parse_img_meta(const pugi::xml_node &node, double &x, double &y, double &width, double &height) {
+    /* Read XML node attributes */
+    x = usvg_double_attr(node, "x", 0.0);
+    y = usvg_double_attr(node, "y", 0.0);
+    width = usvg_double_attr(node, "width", 0.0);
+    height = usvg_double_attr(node, "height", 0.0);
+    assert (width > 0 && height > 0);
+    cerr << "image elem: w="<<width<<", h="<<height<<endl;
+}
+
+string gerbolyze::read_img_data(const pugi::xml_node &node) {
+    /* Read image from data:base64... URL */
+    string img_data = parse_data_iri(node.attribute("xlink:href").value());
+    if (img_data.empty()) {
+        cerr << "Warning: Empty or invalid image element with id \"" << node.attribute("id").value() << "\"" << endl;
+        return "";
+    }
+    return img_data;
+}
+
+cv::Mat read_img_opencv(const pugi::xml_node &node) {
+    string img_data = read_img_data(node);
+
+    /* slightly annoying round-trip through the std:: and cv:: APIs */
+    vector<unsigned char> img_vec(img_data.begin(), img_data.end());
+    cv::Mat data_mat(img_vec, true);
+    cv::Mat img = cv::imdecode(data_mat, cv::ImreadModes::IMREAD_GRAYSCALE | cv::ImreadModes::IMREAD_ANYDEPTH);
+    data_mat.release();
+
+    if (img.empty()) {
+        cerr << "Warning: Could not decode content of image element with id \"" << node.attribute("id").value() << "\"" << endl;
+    }
+
+    return img;
+}
+
+void gerbolyze::draw_bg_rect(cairo_t *cr, double width, double height, ClipperLib::Paths &clip_path, PolygonSink &sink, cairo_matrix_t &viewport_matrix) {
+    /* For both our debug SVG output and for the gerber output, we have to paint the image's bounding box in black as
+     * background for our halftone blobs. We cannot simply draw a rect here, though. Instead we have to first intersect
+     * the bounding box with the clip path we get from the caller, then we have to translate it into Cairo-SVG's
+     * document units. */
+    /* First, setup the bounding box rectangle in our local px coordinate space. */
+    ClipperLib::Path rect_path;
+    for (auto &elem : vector<pair<double, double>> {{0, 0}, {width, 0}, {width, height}, {0, height}}) {
+        double x = elem.first, y = elem.second;
+        cairo_user_to_device(cr, &x, &y);
+        rect_path.push_back({ (ClipperLib::cInt)round(x * clipper_scale), (ClipperLib::cInt)round(y * clipper_scale) });
+    }
+
+    /* Intersect the bounding box with the caller's clip path */
+    ClipperLib::Clipper c;
+    c.AddPath(rect_path, ClipperLib::ptSubject, /* closed */ true);
+    if (!clip_path.empty()) {
+        c.AddPaths(clip_path, ClipperLib::ptClip, /* closed */ true);
+    }
+
+    ClipperLib::Paths rect_out;
+    c.StrictlySimple(true);
+    c.Execute(ClipperLib::ctIntersection, rect_out, ClipperLib::pftNonZero, ClipperLib::pftNonZero);
+
+    /* Finally, translate into Cairo-SVG's document units and draw. */
+    cairo_save(cr);
+    cairo_set_matrix(cr, &viewport_matrix);
+    cairo_new_path(cr);
+    ClipperLib::cairo::clipper_to_cairo(rect_out, cr, CAIRO_PRECISION, ClipperLib::cairo::tNone);
+    cairo_set_source_rgba (cr, 0.0, 0.0, 0.0, 1.0);
+    /* First, draw into SVG */
+    cairo_fill(cr);
+    cairo_restore(cr);
+
+    /* Second, draw into gerber. */
+    for (const auto &poly : rect_out) {
+        vector<array<double, 2>> out;
+        for (const auto &p : poly)
+            out.push_back(std::array<double, 2>{
+                    ((double)p.X) / clipper_scale, ((double)p.Y) / clipper_scale
+                    });
+        sink << GRB_POL_CLEAR << out;
+    }
+}
+
+
+
+/* Render image into gerber file.
+ *
+ * This function renders an image into a number of vector primitives emulating the images grayscale brightness by
+ * differently sized vector shaped giving an effect similar to halftone printing used in newspapers.
+ *
+ * On a high level, this function does this in four steps:
+ * 1. It preprocesses the source image at the pixel level. This involves several tasks:
+ *    1.1. It converts the image to grayscale.
+ *    1.2. It scales the image up or down to match the given minimum feature size.
+ *    1.3. It applies a blur depending on the given minimum feature size to prevent aliasing artifacts.
+ * 2. It randomly spread points across the image using poisson disc sampling. This yields points that have a fairly even
+ *    average distance to each other across the image, and that have a guaranteed minimum distance that depends on
+ *    minimum feature size.
+ * 3. It calculates a voronoi map based on this set of points and it calculats the polygon shape of each cell of the
+ *    voronoi map.
+ * 4. It scales each of these voronoi cell polygons to match the input images brightness at the spot covered by this
+ *    cell.
+ */
+void gerbolyze::VoronoiVectorizer::vectorize_image(cairo_t *cr, const pugi::xml_node &node, ClipperLib::Paths &clip_path, cairo_matrix_t &viewport_matrix, PolygonSink &sink, double min_feature_size_px) {
+    double x, y, width, height;
+    parse_img_meta(node, x, y, width, height);
+    cv::Mat img = read_img_opencv(node);
+    if (img.empty())
+        return;
+
+    cairo_save(cr);
+    /* Set up target transform using SVG transform and x/y attributes */
+    apply_cairo_transform_from_svg(cr, node.attribute("transform").value());
+    cairo_translate(cr, x, y);
+
+    double orig_rows = img.rows;
+    double orig_cols = img.cols;
+    double scale_x = (double)width / orig_cols;
+    double scale_y = (double)height / orig_rows;
+    double off_x = 0;
+    double off_y = 0;
+    handle_aspect_ratio(node.attribute("preserveAspectRatio").value(),
+            scale_x, scale_y, off_x, off_y, orig_cols, orig_rows);
+
+    /* Adjust minimum feature size given in mm and translate into px document units in our local coordinate system. */
+    double f_x = min_feature_size_px, f_y = 0;
+    cairo_device_to_user_distance(cr, &f_x, &f_y);
+    min_feature_size_px = sqrt(f_x*f_x + f_y*f_y);
+
+    draw_bg_rect(cr, width, height, clip_path, sink, viewport_matrix);
+
+    /* Set up a poisson-disc sampled point "grid" covering the image. Calculate poisson disc parameters from given
+     * minimum feature size. */
+    double grayscale_overhead = 0.8; /* fraction of distance between two adjacent cell centers that is reserved for
+                                        grayscale interpolation. Larger values -> better grayscale resolution,
+                                        larger cells. */
+    double center_distance = min_feature_size_px * 2.0 * (1.0 / (1.0-grayscale_overhead));
+    vector<d2p> *grid_centers = get_sampler(m_grid_type)(scale_x * orig_cols, scale_y*orig_rows, center_distance);
+    //vector<d2p> *grid_centers = sample_poisson_disc(width, height, min_feature_size_px * 2.0 * 2.0);
+    //vector<d2p> *grid_centers = sample_hexgrid(width, height, center_distance);
+    //vector<d2p> *grid_centers = sample_squaregrid(width, height, center_distance);
+
+    /* Target factor between given min_feature_size and intermediate image pixels,
+     * i.e. <scale_featuresize_factor> px ^= min_feature_size */
+    double scale_featuresize_factor = 3.0;
+    /* TODO: support for preserveAspectRatio attribute */
+    double px_w = width / min_feature_size_px * scale_featuresize_factor;
+    double px_h = height / min_feature_size_px * scale_featuresize_factor;
+
+    /* Scale intermediate image (step 1.2) to have <scale_featuresize_factor> pixels per min_feature_size. */ 
+    cv::Mat scaled(cv::Size{(int)round(px_w), (int)round(px_h)}, img.type());
+    cv::resize(img, scaled, scaled.size(), 0, 0);
+    cerr << "scaled " << img.cols << ", " << img.rows << " -> " << scaled.cols << ", " << scaled.rows << endl;
+    img.release();
+
+    /* Blur image with a kernel larger than our minimum feature size to avoid aliasing. */
+    cv::Mat blurred(scaled.size(), scaled.type());
+    int blur_size = (int)ceil(fmax(scaled.cols / width, scaled.rows / height) * center_distance);
+    if (blur_size%2 == 0)
+        blur_size += 1;
+    cerr << "blur size " << blur_size << endl;
+    cv::GaussianBlur(scaled, blurred, {blur_size, blur_size}, 0, 0);
+    scaled.release();
+    
+    /* Calculate voronoi diagram for the grid generated above. */
+    jcv_diagram diagram;
+    memset(&diagram, 0, sizeof(jcv_diagram));
+    cerr << "adjusted scale " << scale_x << " " << scale_y << endl;
+    cerr << "voronoi clip rect " << (scale_x * orig_cols) << " " << (scale_y * orig_rows) << endl;
+    jcv_rect rect {{0.0, 0.0}, {scale_x * orig_cols, scale_y * orig_rows}};
+    jcv_point *pts = reinterpret_cast<jcv_point *>(grid_centers->data()); /* hackety hack */
+    jcv_diagram_generate(grid_centers->size(), pts, &rect, 0, &diagram);
+    /* Relax points, i.e. wiggle them around a little bit to equalize differences between cell sizes a little bit. */
+    if (m_relax)
+        voronoi_relax_points(&diagram, pts);
+    memset(&diagram, 0, sizeof(jcv_diagram));
+    jcv_diagram_generate(grid_centers->size(), pts, &rect, 0, &diagram);
+    
+    /* For each voronoi cell calculated above, find the brightness of the blurred image pixel below its center. We do
+     * not have to average over the entire cell's area here: The blur is doing a good approximation of that while being
+     * simpler and faster.
+     *
+     * We do this step before generating the cell poygons below because we have to look up a cell's neighbor's fill
+     * factor during gap filling for minimum feature size preservation. */
+    vector<double> fill_factors(diagram.numsites); /* Factor to be multiplied with site polygon radius to yield target
+                                                      fill level */
+    const jcv_site* sites = jcv_diagram_get_sites(&diagram);
+    int j = 0;
+    for (int i=0; i<diagram.numsites; i++) {
+        const jcv_point center = sites[i].p;
+
+        double pxd = (double)blurred.at<unsigned char>(
+                (int)round(center.y / (scale_y * orig_rows / blurred.rows)),
+                (int)round(center.x / (scale_x * orig_cols / blurred.cols))) / 255.0; 
+        /* FIXME: This is a workaround for a memory corruption bug that happens with the square-grid setting. When using
+         * square-grid on a fairly small test image, sometimes sites[i].index will be out of bounds here.
+         */
+        if (sites[i].index < fill_factors.size())
+            fill_factors[sites[i].index] = sqrt(pxd);
+    }
+
+    /* Minimum gap between adjacent scaled site polygons. */
+    double min_gap_px = min_feature_size_px;
+    vector<double> adjusted_fill_factors;
+    adjusted_fill_factors.reserve(32); /* Vector to hold adjusted fill factors for each edge for gap filling */
+    /* now iterate over all voronoi cells again to generate each cell's scaled polygon halftone blob. */
+    for (int i=0; i<diagram.numsites; i++) {
+        const jcv_point center = sites[i].p;
+        double fill_factor_ours = fill_factors[sites[i].index];
+        
+        /* Do not render halftone blobs that are too small */
+        if (fill_factor_ours * 0.5 * center_distance < min_gap_px)
+            continue;
+
+        /* Iterate over this cell's edges. For each edge, check the gap that would result between this cell's halftone
+         * blob and the neighboring cell's halftone blob based on their fill factors. If the gap is too small, either
+         * widen it by adjusting both fill factors down a bit (for this edge only!), or eliminate it by setting both
+         * fill factors to 1.0 (again, for this edge only!). */
+        adjusted_fill_factors.clear();
+        const jcv_graphedge* e = sites[i].edges;
+        while (e) {
+            /* half distance between both neighbors of this edge, i.e. sites[i] and its neighbor. */
+            /* Note that in a voronoi tesselation, this edge is always halfway between. */
+            double adjusted_fill_factor = fill_factor_ours;
+
+            if (e->neighbor != nullptr) { /* nullptr -> edge is on the voronoi map's border */
+                double rad = sqrt(pow(center.x - e->neighbor->p.x, 2) + pow(center.y - e->neighbor->p.y, 2)) / 2.0;
+                double fill_factor_theirs = fill_factors[e->neighbor->index];
+                double gap_px = (1.0 - fill_factor_ours) * rad + (1.0 - fill_factor_theirs) * rad;
+
+                if (gap_px > min_gap_px) {
+                    /* all good. gap is wider than minimum. */
+                } else if (gap_px > 0.5 * min_gap_px) {
+                    /* gap is narrower than minimum, but more than half of minimum width. */
+                    /* force gap open, distribute adjustment evenly on left/right */
+                    double fill_factor_adjustment = (min_gap_px - gap_px) / 2.0 / rad;
+                    adjusted_fill_factor -= fill_factor_adjustment;
+                } else {
+                    /* gap is less than half of minimum width. Force gap closed. */
+                    adjusted_fill_factor = 1.0;
+                }
+            }
+            adjusted_fill_factors.push_back(adjusted_fill_factor);
+            e = e->next;
+        }
+
+        /* Now, generate the actual halftone blob polygon */
+        ClipperLib::Path cell_path;
+        double last_fill_factor = adjusted_fill_factors.back();
+        e = sites[i].edges;
+        j = 0;
+        while (e) {
+            double fill_factor = adjusted_fill_factors[j];
+            if (last_fill_factor != fill_factor) {
+                /* Fill factor was adjusted since last edge, so generate one extra point so we have a nice radial
+                 * "step". */
+                double x = e->pos[0].x;
+                double y = e->pos[0].y;
+                x = off_x + center.x + (x - center.x) * fill_factor;
+                y = off_y + center.y + (y - center.y) * fill_factor;
+
+                cairo_user_to_device(cr, &x, &y);
+                cell_path.push_back({ (ClipperLib::cInt)round(x * clipper_scale), (ClipperLib::cInt)round(y * clipper_scale) });
+            }
+
+            /* Emit endpoint of current edge */
+            double x = e->pos[1].x;
+            double y = e->pos[1].y;
+            x = off_x + center.x + (x - center.x) * fill_factor;
+            y = off_y + center.y + (y - center.y) * fill_factor;
+
+            cairo_user_to_device(cr, &x, &y);
+            cell_path.push_back({ (ClipperLib::cInt)round(x * clipper_scale), (ClipperLib::cInt)round(y * clipper_scale) });
+
+            j += 1;
+            last_fill_factor = fill_factor;
+            e = e->next;
+        }
+
+        /* Now, clip the halftone blob generated above against the given clip path. We do this individually for each
+         * blob since this way is *much* faster than throwing a million blobs at once at poor clipper. */
+        ClipperLib::Paths polys;
+        ClipperLib::Clipper c;
+        c.AddPath(cell_path, ClipperLib::ptSubject, /* closed */ true);
+        if (!clip_path.empty()) {
+            c.AddPaths(clip_path, ClipperLib::ptClip, /* closed */ true);
+        }
+        c.StrictlySimple(true);
+        c.Execute(ClipperLib::ctIntersection, polys, ClipperLib::pftNonZero, ClipperLib::pftNonZero);
+
+        /* Export halftone blob to debug svg */
+        cairo_save(cr);
+        cairo_set_matrix(cr, &viewport_matrix);
+        cairo_new_path(cr);
+        ClipperLib::cairo::clipper_to_cairo(polys, cr, CAIRO_PRECISION, ClipperLib::cairo::tNone);
+        cairo_set_source_rgba(cr, 1, 1, 1, 1);
+        cairo_fill(cr);
+        cairo_restore(cr);
+
+        /* And finally, export halftone blob to gerber. */
+        for (const auto &poly : polys) {
+            vector<array<double, 2>> out;
+            for (const auto &p : poly)
+                out.push_back(std::array<double, 2>{
+                        ((double)p.X) / clipper_scale, ((double)p.Y) / clipper_scale
+                        });
+            sink << GRB_POL_DARK << out;
+        }
+    }
+
+    blurred.release();
+    jcv_diagram_free( &diagram );
+    delete grid_centers;
+    cairo_restore(cr);
+}
+
+void gerbolyze::handle_aspect_ratio(string spec, double &scale_x, double &scale_y, double &off_x, double &off_y, double cols, double rows) {
+
+    if (spec.empty()) {
+        spec = "xMidYMid meet";
+    }
+
+    auto idx = spec.find(" ");
+    string par_align = spec;
+    string par_meet = "meet";
+    if (idx != string::npos) {
+        par_align = spec.substr(0, idx);
+        par_meet = spec.substr(idx+1);
+    }
+
+    if (par_align != "none") {
+        double scale = scale_x;
+        if (par_meet == "slice") {
+            scale = std::max(scale_x, scale_y);
+        } else {
+            scale = std::min(scale_x, scale_y);
+        }
+
+        std::regex reg("x(Min|Mid|Max)Y(Min|Mid|Max)");
+        std::smatch match;
+
+        cerr << "data: " <<" "<< scale_x << "/" << scale_y << ": " << scale << endl;
+        off_x = (scale_x - scale) * cols;
+        off_y = (scale_y - scale) * rows;
+        cerr << rows <<","<<cols<<" " << off_x << "," << off_y << endl;
+        if (std::regex_match(par_align, match, reg)) {
+            assert (match.size() == 3);
+            if (match[1].str() == "Min") {
+                off_x = 0;
+            } else if (match[1].str() == "Mid") {
+                off_x *= 0.5;
+            }
+
+            if (match[2].str() == "Min") {
+                off_y = 0;
+            } else if (match[2].str() == "Mid") {
+                off_y *= 0.5;
+            }
+
+        } else {
+            cerr << "Invalid preserveAspectRatio meetOrSlice value \"" << par_align << "\"" << endl;
+            off_x *= 0.5;
+            off_y *= 0.5;
+        }
+
+        scale_x = scale_y = scale;
+    }
+    cerr << "res: "<< off_x << "," << off_y << endl;
+}
+
+
+void gerbolyze::OpenCVContoursVectorizer::vectorize_image(cairo_t *cr, const pugi::xml_node &node, ClipperLib::Paths &clip_path, cairo_matrix_t &viewport_matrix, PolygonSink &sink, double min_feature_size_px) {
+    double x, y, width, height;
+    parse_img_meta(node, x, y, width, height);
+    cv::Mat img = read_img_opencv(node);
+    if (img.empty())
+        return;
+
+    cairo_save(cr);
+    /* Set up target transform using SVG transform and x/y attributes */
+    apply_cairo_transform_from_svg(cr, node.attribute("transform").value());
+    cairo_translate(cr, x, y);
+
+    double scale_x = (double)width / (double)img.cols;
+    double scale_y = (double)height / (double)img.rows;
+    double off_x = 0;
+    double off_y = 0;
+    handle_aspect_ratio(node.attribute("preserveAspectRatio").value(),
+            scale_x, scale_y, off_x, off_y, img.cols, img.rows);
+
+    draw_bg_rect(cr, width, height, clip_path, sink, viewport_matrix);
+
+    vector<vector<cv::Point>> contours;
+    vector<cv::Vec4i> hierarchy;
+    cv::findContours(img, contours, hierarchy, cv::RETR_TREE, cv::CHAIN_APPROX_TC89_KCOS);
+
+    queue<pair<size_t, bool>> child_stack;
+    child_stack.push({ 0, true });
+
+    while (!child_stack.empty()) {
+        bool dark = child_stack.front().second;
+        for (int i=child_stack.front().first; i>=0; i = hierarchy[i][0]) {
+            if (hierarchy[i][2] >= 0) {
+                child_stack.push({ hierarchy[i][2], !dark });
+            }
+
+            sink << (dark ? GRB_POL_DARK : GRB_POL_CLEAR);
+
+            bool is_clockwise = cv::contourArea(contours[i], true) > 0;
+            if (!is_clockwise)
+                std::reverse(contours[i].begin(), contours[i].end());
+
+            ClipperLib::Path out;
+            for (const auto &p : contours[i]) {
+                double x = off_x + (double)p.x * scale_x;
+                double y = off_y + (double)p.y * scale_y;
+                cairo_user_to_device(cr, &x, &y);
+                out.push_back({ (ClipperLib::cInt)round(x * clipper_scale), (ClipperLib::cInt)round(y * clipper_scale) });
+            }
+
+            ClipperLib::Clipper c;
+            c.AddPath(out, ClipperLib::ptSubject, /* closed */ true);
+            if (!clip_path.empty()) {
+                c.AddPaths(clip_path, ClipperLib::ptClip, /* closed */ true);
+            }
+            c.StrictlySimple(true);
+            ClipperLib::Paths polys;
+            c.Execute(ClipperLib::ctIntersection, polys, ClipperLib::pftNonZero, ClipperLib::pftNonZero);
+
+            /* Finally, translate into Cairo-SVG's document units and draw. */
+            cairo_save(cr);
+            cairo_set_matrix(cr, &viewport_matrix);
+            cairo_new_path(cr);
+            ClipperLib::cairo::clipper_to_cairo(polys, cr, CAIRO_PRECISION, ClipperLib::cairo::tNone);
+            cairo_set_source_rgba (cr, 0.0, 0.0, 0.0, 1.0);
+            /* First, draw into SVG */
+            cairo_fill(cr);
+            cairo_restore(cr);
+
+            /* Second, draw into gerber. */
+            for (const auto &poly : polys) {
+                vector<array<double, 2>> out;
+                for (const auto &p : poly)
+                    out.push_back(std::array<double, 2>{
+                            ((double)p.X) / clipper_scale, ((double)p.Y) / clipper_scale
+                            });
+                sink << out;
+            }
+        }
+
+        child_stack.pop();
+    }
+
+    cairo_restore(cr);
+}
+
+gerbolyze::VectorizerSelectorizer::VectorizerSelectorizer(const string default_vectorizer, const string defs)
+    : m_default(default_vectorizer) {
+    istringstream foo(defs);
+    string elem;
+    while (std::getline(foo, elem, ',')) {
+        size_t pos = elem.find_first_of("=");
+        if (pos == string::npos) {
+            cerr << "Error parsing vectorizer selection string at element \"" << elem << "\"" << endl;
+            continue;
+        }
+
+        const string parsed_id = elem.substr(0, pos);
+        const string mapping = elem.substr(pos+1);
+        m_map[parsed_id] = mapping;
+    }
+
+    cerr << "parsed " << m_map.size() << " vectorizers" << endl;
+    for (auto &elem : m_map) {
+        cerr << "  " << elem.first << " -> " << elem.second << endl;
+    }
+}
+
+ImageVectorizer *gerbolyze::VectorizerSelectorizer::select(const pugi::xml_node &img) {
+    const string id = img.attribute("id").value();
+    cerr << "selecting vectorizer for image \"" << id << "\"" << endl;
+    if (m_map.contains(id)) {
+        cerr << "  -> found" << endl;
+        return makeVectorizer(m_map[id]);
+    }
+
+    cerr << "  -> default" << endl;
+    return makeVectorizer(m_default);
+}
+
diff --git a/svg-flatten/src/vec_core.h b/svg-flatten/src/vec_core.h
new file mode 100644
index 0000000..8267fd1
--- /dev/null
+++ b/svg-flatten/src/vec_core.h
@@ -0,0 +1,58 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <cairo.h>
+#include <pugixml.hpp>
+#include <clipper.hpp>
+#include <gerbolyze.hpp>
+#include "vec_grid.h"
+
+namespace gerbolyze {
+
+    class VoronoiVectorizer : public ImageVectorizer {
+    public:
+        VoronoiVectorizer(grid_type grid, bool relax=true) : m_relax(relax), m_grid_type(grid) {}
+
+        virtual void vectorize_image(cairo_t *cr, const pugi::xml_node &node, ClipperLib::Paths &clip_path, cairo_matrix_t &viewport_matrix, PolygonSink &sink, double min_feature_size_px);
+    private:
+        double m_relax;
+        grid_type m_grid_type;
+    };
+
+    class OpenCVContoursVectorizer : public ImageVectorizer {
+    public:
+        OpenCVContoursVectorizer() {}
+
+        virtual void vectorize_image(cairo_t *cr, const pugi::xml_node &node, ClipperLib::Paths &clip_path, cairo_matrix_t &viewport_matrix, PolygonSink &sink, double min_feature_size_px);
+    };
+
+    class DevNullVectorizer : public ImageVectorizer {
+    public:
+        DevNullVectorizer() {}
+
+        virtual void vectorize_image(cairo_t *, const pugi::xml_node &, ClipperLib::Paths &, cairo_matrix_t &, PolygonSink &, double) {}
+    };
+
+    void parse_img_meta(const pugi::xml_node &node, double &x, double &y, double &width, double &height);
+    std::string read_img_data(const pugi::xml_node &node);
+    void draw_bg_rect(cairo_t *cr, double width, double height, ClipperLib::Paths &clip_path, PolygonSink &sink, cairo_matrix_t &viewport_matrix);
+    void handle_aspect_ratio(std::string spec, double &scale_x, double &scale_y, double &off_x, double &off_y, double cols, double rows);
+}
+
diff --git a/svg-flatten/src/vec_grid.cpp b/svg-flatten/src/vec_grid.cpp
new file mode 100644
index 0000000..7c27543
--- /dev/null
+++ b/svg-flatten/src/vec_grid.cpp
@@ -0,0 +1,99 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "poisson_disk_sampling.h"
+
+#include "vec_grid.h"
+
+using namespace std;
+using namespace gerbolyze;
+
+sampling_fun gerbolyze::get_sampler(enum grid_type type) {
+    switch(type) {
+        case POISSON_DISC:
+            return sample_poisson_disc;
+        case HEXGRID:
+            return sample_hexgrid;
+        case SQUAREGRID:
+            return sample_squaregrid;
+        default:
+            return sample_poisson_disc;
+    }
+}
+
+vector<d2p> *gerbolyze::sample_poisson_disc(double w, double h, double center_distance) {
+    d2p top_left {0, 0};
+    d2p bottom_right {w, h};
+    return new auto(thinks::PoissonDiskSampling(center_distance/2.5, top_left, bottom_right));
+}
+
+vector<d2p> *gerbolyze::sample_hexgrid(double w, double h, double center_distance) {
+    double radius = center_distance / 2.0 / (sqrt(3) / 2.0); /* radius of hexagon */
+    double pitch_v = 1.5 * radius;
+    double pitch_h = center_distance;
+
+    /* offset of first hexagon to make sure the entire area is covered. We use slightly larger values here to avoid
+     * corner cases during clipping in the voronoi map generator.  The inaccuracies this causes at the edges are
+     * negligible. */
+    double off_x = 0.5001 * center_distance;
+    double off_y = 0.5001 * radius;
+
+    /* NOTE: The voronoi generator is not quite stable when points lie outside the bounds. Thus, floor(). */
+    long long int points_x = floor(w / pitch_h);
+    long long int points_y = floor(h / pitch_v);
+
+    vector<d2p> *out = new vector<d2p>();
+    out->reserve((points_x+1) * points_y);
+
+    /* This may generate up to one extra row of points. We don't care since these points will simply be clipped during
+     * voronoi map generation. */
+    for (long long int y_i=0; y_i<points_y; y_i+=2) {
+        for (long long int x_i=0; x_i<points_x; x_i++) { /* allow one extra point to compensate for row shift */
+            out->push_back(d2p{off_x + x_i * pitch_h, off_y + y_i * pitch_v});
+        }
+
+        for (long long int x_i=0; x_i<points_x+1; x_i++) { /* allow one extra point to compensate for row shift */
+            out->push_back(d2p{off_x + (x_i - 0.5) * pitch_h, off_y + (y_i + 1) * pitch_v});
+        }
+    }
+
+    return out;
+}
+
+vector<d2p> *gerbolyze::sample_squaregrid(double w, double h, double center_distance) {
+    /* offset of first square to make sure the entire area is covered. We use slightly larger values here to avoid
+     * corner cases during clipping in the voronoi map generator.  The inaccuracies this causes at the edges are
+     * negligible. */
+    double off_x = 0.5 * center_distance;
+    double off_y = 0.5 * center_distance;
+
+    long long int points_x = ceil(w / center_distance);
+    long long int points_y = ceil(h / center_distance);
+
+    vector<d2p> *out = new vector<d2p>();
+    out->reserve(points_x * points_y);
+
+    for (long long int y_i=0; y_i<points_y; y_i++) {
+        for (long long int x_i=0; x_i<points_x; x_i++) {
+            out->push_back({off_x + x_i*center_distance, off_y + y_i*center_distance});
+        }
+    }
+
+    return out;
+}
+
diff --git a/svg-flatten/src/vec_grid.h b/svg-flatten/src/vec_grid.h
new file mode 100644
index 0000000..f2ed55a
--- /dev/null
+++ b/svg-flatten/src/vec_grid.h
@@ -0,0 +1,41 @@
+/*
+ * This file is part of gerbolyze, a vector image preprocessing toolchain 
+ * Copyright (C) 2021 Jan Sebastian Götte <gerbolyze@jaseg.de>
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <array>
+#include <vector>
+#include <functional>
+#include <gerbolyze.hpp>
+
+namespace gerbolyze {
+
+enum grid_type {
+    POISSON_DISC,
+    HEXGRID,
+    SQUAREGRID
+};
+
+sampling_fun get_sampler(enum grid_type type);
+
+std::vector<d2p> *sample_poisson_disc(double w, double h, double center_distance);
+std::vector<d2p> *sample_hexgrid(double w, double h, double center_distance);
+std::vector<d2p> *sample_squaregrid(double w, double h, double center_distance);
+
+} /* namespace gerbolyze */
+