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diff --git a/src/vec_core.cpp b/src/vec_core.cpp
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+/*
+ * 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);
+}
+
+