Reorg: move svg-flatten files into subdir

1 files changed, 567 insertions, 0 deletions

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);
+}
+