Initial commit

17 files changed, 2184 insertions, 0 deletions

diff --git a/src/svg_color.cpp b/src/svg_color.cpp
new file mode 100644
index 0000000..acd793d
--- /dev/null
+++ b/src/svg_color.cpp
@@ -0,0 +1,125 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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
+ */
+
+#include "svg_color.h"
+
+#include <assert.h>
+#include <string>
+#include <cmath>
+
+using namespace svg_plugin;
+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 svg_plugin::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;
+}
+
+svg_plugin::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;
+};
+
+svg_plugin::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 svg_plugin::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 svg_plugin::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 svg_plugin::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/src/svg_color.h b/src/svg_color.h
new file mode 100644
index 0000000..5183dab
--- /dev/null
+++ b/src/svg_color.h
@@ -0,0 +1,59 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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_COLOR_H
+#define SVG_COLOR_H
+
+#include <pugixml.hpp>
+
+namespace svg_plugin {
+
+/* 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 svg_plugin */
+
+#endif /* SVG_COLOR_H */
diff --git a/src/svg_doc.cpp b/src/svg_doc.cpp
new file mode 100644
index 0000000..2543146
--- /dev/null
+++ b/src/svg_doc.cpp
@@ -0,0 +1,462 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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
+ */
+
+#include "svg_import_defs.h"
+#include "svg_doc.h"
+#include "svg_color.h"
+#include "svg_geom.h"
+#include "svg_path.h"
+#include "vec_core.h"
+
+using namespace svg_plugin;
+using namespace std;
+using namespace ClipperLib;
+using namespace vectorizer;
+
+svg_plugin::SVGDocument::~SVGDocument() {
+    if (cr)
+        cairo_destroy (cr);
+    if (surface)
+        cairo_surface_destroy (surface);
+}
+
+bool svg_plugin::SVGDocument::load(string filename, string debug_out_filename) {
+    /* Load XML document */
+    auto res = svg_doc.load_file(filename.c_str());
+    if (!res) {
+        cerr << "Cannot open input file \"" << filename << "\": " << res << endl;
+        return false;
+    }
+
+    root_elem = svg_doc.child("svg");
+    if (!root_elem) {
+        cerr << "Cannot load input file \"" << filename << 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 *svg_plugin::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 *svg_plugin::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 svg_plugin::SVGDocument::mm_to_doc_units(double mm) const {
+    return mm * (vb_w / page_w_mm);
+}
+
+double svg_plugin::SVGDocument::doc_units_to_mm(double px) const {
+    return px / (vb_w / page_w_mm);
+}
+
+/* Recursively export all SVG elements in the given group. */
+void svg_plugin::SVGDocument::export_svg_group(const pugi::xml_node &group, Paths &parent_clip_path) {
+    /* 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()) {
+            cerr << "Combining clip paths" << endl;
+            combine_clip_paths(parent_clip_path, clip_path, clip_path);
+        } else {
+            cerr << "using parent clip path" << endl;
+            clip_path = parent_clip_path;
+        }
+    }
+
+    ClipperLib::Clipper c2;
+    c2.AddPaths(clip_path, ptSubject, /* closed */ true);
+    ClipperLib::IntRect bbox = c2.GetBounds();
+    cerr << "clip path is now: bbox={" << bbox.left << ", " << bbox.top << "} - {" << bbox.right << ", " << bbox.bottom << "}" << endl;
+
+    /* Iterate over the group's children, exporting them one by one. */
+    for (const auto &node : group.children()) {
+        string name(node.name());
+        if (name == "g") {
+            export_svg_group(node, clip_path);
+
+        } else if (name == "path") {
+            export_svg_path(node, clip_path);
+
+        } else if (name == "image") {
+            double min_feature_size_mm = 0.1; /* TODO make configurable */
+            double min_feature_size_px = mm_to_doc_units(min_feature_size_mm);
+            vectorize_image(cr, node, min_feature_size_px, clip_path, viewport_matrix);
+        } 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 svg_plugin::SVGDocument::export_svg_path(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(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
+                            });
+                std::cerr << "calling sink" << std::endl;
+                polygon_sink(out, fill_color == GRB_DARK);
+            }
+            cairo_restore(cr);
+        }
+    }
+
+    if (stroke_color && stroke_width > 0.0) {
+        ClipperOffset offx;
+
+        /* 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(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
+                            });
+                std::cerr << "calling sink" << std::endl;
+                polygon_sink(out, stroke_color == GRB_DARK);
+            }
+            cairo_restore(cr);
+        }
+    }
+}
+
+void svg_plugin::SVGDocument::do_export(string debug_out_filename) {
+    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.
+     */
+    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(root_elem, vb_paths);
+}
+
+void svg_plugin::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 svg_plugin::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) });
+        cerr << "adding to path: " << (cInt)round(x * clipper_scale) << ", " << (cInt)round(y * clipper_scale) << endl;
+    }
+    vb_paths.push_back(vb_path);
+
+    ClipperLib::Clipper c;
+    c.AddPaths(vb_paths, ptSubject, /* closed */ true);
+    ClipperLib::IntRect bbox = c.GetBounds();
+    cerr << "did set up viewbox clip: bbox={" << bbox.left << ", " << bbox.top << "} - {" << bbox.right << ", " << bbox.bottom << "}" << endl;
+    export_svg_group(root_elem, vb_paths);
+}
+
+void svg_plugin::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 svg_plugin::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);
+    }
+}
+
diff --git a/src/svg_doc.h b/src/svg_doc.h
new file mode 100644
index 0000000..01a4e7a
--- /dev/null
+++ b/src/svg_doc.h
@@ -0,0 +1,97 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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_DOC_H
+#define SVG_DOC_H
+
+#include <map>
+
+#include <pugixml.hpp>
+
+#include "svg_pattern.h"
+
+namespace svg_plugin {
+
+    typedef std::function<void (std::vector<std::array<double, 2>>, bool)> polygon_sink_fun;
+
+    class SVGDocument {
+    public:
+        SVGDocument() : _valid(false) {}
+        SVGDocument(polygon_sink_fun sink_fun) : _valid(false), polygon_sink(sink_fun) {}
+        ~SVGDocument();
+
+        /* true -> load successful */
+        bool load(std::string filename, std::string debug_out_filename="/tmp/kicad_svg_debug.svg");
+        /* true -> load successful */
+        bool valid() const { return _valid; }
+        operator bool() const { return valid(); }
+
+        double mm_to_doc_units(double) const;
+        double doc_units_to_mm(double) const;
+
+        double width() const { return page_w_mm; }
+        double height() const { return page_h_mm; }
+
+        void do_export(std::string debug_out_filename="");
+
+    private:
+        friend class Pattern;
+
+        cairo_t *cairo() { return cr; }
+        const ClipperLib::Paths *lookup_clip_path(const pugi::xml_node &node);
+        Pattern *lookup_pattern(const std::string id);
+
+        void export_svg_group(const pugi::xml_node &group, ClipperLib::Paths &parent_clip_path);
+        void export_svg_path(const pugi::xml_node &node, ClipperLib::Paths &clip_path);
+        void setup_debug_output(std::string filename="");
+        void setup_viewport_clip();
+        void load_clips();
+        void load_patterns();
+
+        bool _valid;
+        pugi::xml_document svg_doc;
+        pugi::xml_node root_elem;
+        pugi::xml_node defs_node;
+        double vb_x, vb_y, vb_w, vb_h;
+        double page_w, page_h;
+        double page_w_mm, page_h_mm;
+        std::map<std::string, Pattern> pattern_map;
+        std::map<std::string, ClipperLib::Paths> clip_path_map;
+        cairo_matrix_t viewport_matrix;
+        ClipperLib::Paths vb_paths; /* viewport clip rect */
+
+        cairo_t *cr = nullptr;
+        cairo_surface_t *surface = nullptr;
+
+        polygon_sink_fun polygon_sink;
+
+        static constexpr double dbg_fill_alpha = 0.8;
+        static constexpr double dbg_stroke_alpha = 1.0;
+        static constexpr double assumed_usvg_dpi = 96.0;
+    };
+
+} /* namespace svg_plugin */
+
+#endif /* SVG_DOC_H */
+
diff --git a/src/svg_geom.cpp b/src/svg_geom.cpp
new file mode 100644
index 0000000..0e40e7b
--- /dev/null
+++ b/src/svg_geom.cpp
@@ -0,0 +1,181 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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
+ */
+
+#include "svg_geom.h"
+
+#include <cmath>
+#include <string>
+#include <sstream>
+#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 svg_plugin::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 svg_plugin::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 svg_plugin::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 svg_plugin::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;
+}
+
+/* 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 svg_plugin::dehole_polytree(PolyNode &ptree, Paths &out) {
+    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(*child, out);
+            }
+        }
+
+        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);
+
+            PolyTree solution;
+            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, solution, pftNonZero);
+            dehole_polytree(solution, out);
+
+            c.Execute(ctIntersection, solution, pftNonZero);
+            dehole_polytree(solution, out);
+        }
+    }
+}
+
+/* Intersect two clip paths. Both must share a coordinate system. */
+void svg_plugin::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 svg_plugin::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/src/svg_geom.h b/src/svg_geom.h
new file mode 100644
index 0000000..dfd1c80
--- /dev/null
+++ b/src/svg_geom.h
@@ -0,0 +1,44 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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_GEOM_H
+#define SVG_GEOM_H
+
+#include <cairo.h>
+#include <clipper.hpp>
+#include <pugixml.hpp>
+
+namespace svg_plugin {
+
+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::PolyNode &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 svg_plugin */
+
+#endif /* SVG_GEOM_H */
diff --git a/src/svg_import_defs.h b/src/svg_import_defs.h
new file mode 100644
index 0000000..e25c52c
--- /dev/null
+++ b/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/src/svg_import_util.cpp b/src/svg_import_util.cpp
new file mode 100644
index 0000000..5624bd9
--- /dev/null
+++ b/src/svg_import_util.cpp
@@ -0,0 +1,129 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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
+ */
+
+#include <cmath>
+#include "base64.h"
+#include "svg_import_util.h"
+
+using namespace std;
+
+void svg_plugin::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 svg_plugin::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 svg_plugin::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;
+}
+
+svg_plugin::RelativeUnits svg_plugin::map_str_to_units(string str, svg_plugin::RelativeUnits default_val) {
+    if (str == "objectBoundingBox")
+        return SVG_ObjectBoundingBox;
+    else if (str == "userSpaceOnUse")
+        return SVG_UserSpaceOnUse;
+    return default_val;
+}
+
+void svg_plugin::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 svg_plugin::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 svg_plugin::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 svg_plugin::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/src/svg_import_util.h b/src/svg_import_util.h
new file mode 100644
index 0000000..8485957
--- /dev/null
+++ b/src/svg_import_util.h
@@ -0,0 +1,69 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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_UTIL_H
+#define SVG_IMPORT_UTIL_H
+
+#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 svg_plugin {
+
+/* 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 svg_plugin */
+
+#endif /* SVG_IMPORT_UTIL_H */
diff --git a/src/svg_path.cpp b/src/svg_path.cpp
new file mode 100644
index 0000000..9137e1a
--- /dev/null
+++ b/src/svg_path.cpp
@@ -0,0 +1,219 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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
+ */
+
+#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 svg_plugin::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 svg_plugin::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 svg_plugin::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/src/svg_path.h b/src/svg_path.h
new file mode 100644
index 0000000..0a527f6
--- /dev/null
+++ b/src/svg_path.h
@@ -0,0 +1,38 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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_PATH_H
+#define SVG_PATH_H
+
+#include <vector>
+#include <cairo.h>
+#include "svg_geom.h"
+
+namespace svg_plugin {
+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);
+}
+
+#endif /* SVG_PATH_H */
diff --git a/src/svg_pattern.cpp b/src/svg_pattern.cpp
new file mode 100644
index 0000000..8ca6572
--- /dev/null
+++ b/src/svg_pattern.cpp
@@ -0,0 +1,119 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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
+ */
+
+#include <assert.h>
+#include "svg_import_util.h"
+#include "svg_pattern.h"
+#include "svg_import_defs.h"
+#include "svg_geom.h"
+#include "svg_doc.h"
+
+using namespace std;
+
+svg_plugin::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 svg_plugin::Pattern::tile (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(_node, clip);
+            cairo_restore(cr);
+        }
+    }
+    cairo_restore(cr);
+}
+
diff --git a/src/svg_pattern.h b/src/svg_pattern.h
new file mode 100644
index 0000000..e11fde5
--- /dev/null
+++ b/src/svg_pattern.h
@@ -0,0 +1,60 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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_PATTERN_H
+#define SVG_PATTERN_H
+
+#include <string>
+#include <cairo.h>
+
+#include <pugixml.hpp>
+#include <clipper.hpp>
+
+#include "svg_import_util.h"
+
+namespace svg_plugin {
+
+class SVGDocument;
+
+class Pattern {
+public:
+    Pattern() {}
+    Pattern(const pugi::xml_node &node, SVGDocument &doc);
+
+    void tile (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 svg_plugin */
+
+#endif /* SVG_PATTERN_H */
diff --git a/src/vec_core.cpp b/src/vec_core.cpp
new file mode 100644
index 0000000..0c60c7d
--- /dev/null
+++ b/src/vec_core.cpp
@@ -0,0 +1,339 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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
+ */
+
+#include <cmath>
+#include <string>
+#include <iostream>
+#include <vector>
+#include <opencv2/opencv.hpp>
+#include "svg_import_util.h"
+#include "vec_core.h"
+#include "svg_import_defs.h"
+#include "jc_voronoi.h"
+
+using namespace svg_plugin;
+using namespace std;
+
+/* 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;
+    }
+} 
+
+/* 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 vectorizer::vectorize_image(cairo_t *cr, const pugi::xml_node &node, double min_feature_size_px, ClipperLib::Paths &clip_path, cairo_matrix_t &viewport_matrix) {
+    /* Read XML node attributes */
+    auto x = usvg_double_attr(node, "x", 0.0);
+    auto y = usvg_double_attr(node, "y", 0.0);
+    auto width = usvg_double_attr(node, "width", 0.0);
+    auto height = usvg_double_attr(node, "height", 0.0);
+    assert (width > 0 && height > 0);
+    cerr << "image elem: w="<<width<<", h="<<height<<endl;
+
+    /* 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;
+    }
+
+    /* 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;
+    }
+
+    /* Set up target transform using SVG transform and x/y attributes */
+    cairo_save(cr);
+    apply_cairo_transform_from_svg(cr, node.attribute("transform").value());
+    cairo_translate(cr, x, y);
+
+    /* 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);
+
+    /* 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. */
+    cairo_save(cr);
+    cairo_identity_matrix(cr);
+    for (const auto &poly : rect_out) {
+        /* FIXME */
+        //export_as_gerber(cr, poly, /* dark */ false);
+    }
+    cairo_restore(cr);
+
+    /* 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 = sample_poisson_disc(width, height, min_feature_size_px * 2.0 * 2.0);
+    /* TODO make these alternative grids available to callers */
+    //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);
+    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);
+    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));
+    jcv_rect rect {{0.0, 0.0}, {width, height}};
+    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. */
+    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 / height * blurred.rows),
+                (int)round(center.x / width * blurred.cols)) / 255.0; 
+        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 = center.x + (x - center.x) * fill_factor;
+                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 = center.x + (x - center.x) * fill_factor;
+            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. */
+        cairo_save(cr);
+        cairo_identity_matrix(cr);
+        for (const auto &poly : polys) {
+            /* FIXME */
+            //export_as_gerber(cr, poly, /* dark */ true);
+        }
+        cairo_restore(cr);
+    }
+
+    blurred.release();
+    jcv_diagram_free( &diagram );
+    delete grid_centers;
+    cairo_restore(cr);
+}
+
+
diff --git a/src/vec_core.h b/src/vec_core.h
new file mode 100644
index 0000000..20ffd24
--- /dev/null
+++ b/src/vec_core.h
@@ -0,0 +1,37 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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 VEC_CORE_H
+#define VEC_CORE_H
+
+#include <cairo.h>
+#include <pugixml.hpp>
+#include <clipper.hpp>
+#include "vec_grid.h"
+
+namespace vectorizer {
+    void vectorize_image(cairo_t *cr, const pugi::xml_node &node, double min_feature_size_px, ClipperLib::Paths &clip_path, cairo_matrix_t &viewport_matrix);
+}
+
+#endif /* VEC_CORE_H */
diff --git a/src/vec_grid.cpp b/src/vec_grid.cpp
new file mode 100644
index 0000000..0a3eaa2
--- /dev/null
+++ b/src/vec_grid.cpp
@@ -0,0 +1,105 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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
+ */
+
+#include "poisson_disk_sampling.h"
+
+#include "vec_grid.h"
+
+using namespace std;
+using namespace vectorizer;
+
+sampling_fun vectorizer::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> *vectorizer::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, top_left, bottom_right));
+}
+
+vector<d2p> *vectorizer::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> *vectorizer::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/src/vec_grid.h b/src/vec_grid.h
new file mode 100644
index 0000000..cdd61df
--- /dev/null
+++ b/src/vec_grid.h
@@ -0,0 +1,52 @@
+/*
+ * This program source code file is part of KICAD, a free EDA CAD application.
+ *
+ * Copyright (C) 2021 Jan Sebastian Götte <kicad@jaseg.de>
+ * Copyright (C) 2021 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 VEC_GRID_H
+#define VEC_GRID_H
+
+#include <array>
+#include <vector>
+#include <functional>
+
+namespace vectorizer {
+
+typedef std::array<double, 2> d2p;
+
+enum grid_type {
+    POISSON_DISC,
+    HEXGRID,
+    SQUAREGRID
+};
+
+typedef std::function<std::vector<d2p> *(double, double, double)> sampling_fun;
+
+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 vectorizer */
+
+#endif /* VEC_GRID_H */