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diff --git a/src/svg_doc.cpp b/src/svg_doc.cpp
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+++ b/src/svg_doc.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 "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);
+    }
+}
+