Collect various rendering params into new RenderContext object

10 files changed, 229 insertions, 173 deletions

diff --git a/svg-flatten/include/gerbolyze.hpp b/svg-flatten/include/gerbolyze.hpp
index 7b70501..2c21173 100644
--- a/svg-flatten/include/gerbolyze.hpp
+++ b/svg-flatten/include/gerbolyze.hpp
@@ -110,13 +110,13 @@ namespace gerbolyze {
             GerberPolarityToken m_current_polarity = GRB_POL_DARK;
     };
 
-    class Scaler : public PolygonSink {
+    class PolygonScaler : public PolygonSink {
         public:
-            Scaler(PolygonSink &sink, double scale=1.0) : m_sink(sink), m_scale(scale) {}
+            PolygonScaler(PolygonSink &sink, double scale=1.0) : m_sink(sink), m_scale(scale) {}
             virtual void header(d2p origin, d2p size);
-            virtual Scaler &operator<<(const Polygon &poly);
-            virtual Scaler &operator<<(const LayerNameToken &layer_name);
-            virtual Scaler &operator<<(GerberPolarityToken pol);
+            virtual PolygonScaler &operator<<(const Polygon &poly);
+            virtual PolygonScaler &operator<<(const LayerNameToken &layer_name);
+            virtual PolygonScaler &operator<<(GerberPolarityToken pol);
             virtual void footer();
 
         private:
@@ -143,7 +143,10 @@ namespace gerbolyze {
 
     class ElementSelector {
     public:
-        virtual bool match(const pugi::xml_node &node, bool included, bool is_root) const = 0;
+        virtual bool match(const pugi::xml_node &node, bool included, bool is_root) const {
+            (void) node, (void) included, (void) is_root;
+            return true;
+        }
     };
 
     class IDElementSelector : public ElementSelector {
@@ -158,7 +161,7 @@ namespace gerbolyze {
     class ImageVectorizer {
     public:
         virtual ~ImageVectorizer() {};
-        virtual void vectorize_image(xform2d &mat, const pugi::xml_node &node, ClipperLib::Paths &clip_path, PolygonSink &sink, double min_feature_size_px) = 0;
+        virtual void vectorize_image(RenderContext &ctx, const pugi::xml_node &node, double min_feature_size_px) = 0;
     };
     
     ImageVectorizer *makeVectorizer(const std::string &name);
@@ -183,6 +186,42 @@ namespace gerbolyze {
         bool flip_color_interpretation = false;
     };
 
+    class RenderContext {
+        public:
+            RenderContext(const RenderSettings &settings,
+                    PolygonSink &sink,
+                    const ElementSelector &sel,
+                    ClipperLib::Paths &clip);
+            RenderContext(RenderContext &parent,
+                    xform2d transform);
+            RenderContext(RenderContext &parent,
+                    xform2d transform,
+                    ClipperLib::Paths &clip);
+
+            PolygonSink &sink() { return m_sink; }
+            const ElementSelector &sel() { return m_sel; }
+            const RenderSettings &settings() { return m_settings; }
+            xform2d &mat() { return m_mat; }
+            bool root() const { return m_root; }
+            bool included() const { return m_included; }
+            ClipperLib::Paths &clip() { return m_clip; }
+            void transform(xform2d &transform) {
+                m_mat.transform(transform);
+            }
+            bool match(const pugi::xml_node &node) {
+                return m_sel.match(node, m_included, m_root);
+            }
+
+        private:
+            PolygonSink &m_sink;
+            const RenderSettings &m_settings;
+            xform2d m_mat;
+            bool m_root;
+            bool m_included; /* TODO: refactor name */
+            const ElementSelector &m_sel;
+            ClipperLib::Paths &m_clip;
+    };
+
     class SVGDocument {
         public:
             SVGDocument() : _valid(false) {}
@@ -200,8 +239,8 @@ namespace gerbolyze {
             double width() const { return page_w_mm; }
             double height() const { return page_h_mm; }
 
-            void render(const RenderSettings &rset, PolygonSink &sink, const ElementSelector *sel=nullptr);
-            void render_to_list(const RenderSettings &rset, std::vector<std::pair<Polygon, GerberPolarityToken>> &out, const ElementSelector *sel=nullptr);
+            void render(const RenderSettings &rset, PolygonSink &sink, const ElementSelector &sel=ElementSelector());
+            void render_to_list(const RenderSettings &rset, std::vector<std::pair<Polygon, GerberPolarityToken>> &out, const ElementSelector &sel=ElementSelector());
 
         private:
             friend class Pattern;
@@ -209,8 +248,8 @@ namespace gerbolyze {
             const ClipperLib::Paths *lookup_clip_path(const pugi::xml_node &node);
             Pattern *lookup_pattern(const std::string id);
 
-            void export_svg_group(xform2d &mat, const RenderSettings &rset, const pugi::xml_node &group, ClipperLib::Paths &parent_clip_path, const ElementSelector *sel=nullptr, bool included=true, bool is_root=false);
-            void export_svg_path(xform2d &mat, const RenderSettings &rset, const pugi::xml_node &node, ClipperLib::Paths &clip_path);
+            void export_svg_group(RenderContext &ctx, const pugi::xml_node &group);
+            void export_svg_path(RenderContext &ctx, const pugi::xml_node &node);
             void setup_viewport_clip();
             void load_clips(const RenderSettings &rset);
             void load_patterns();
@@ -226,8 +265,6 @@ namespace gerbolyze {
             std::map<std::string, ClipperLib::Paths> clip_path_map;
             ClipperLib::Paths vb_paths; /* viewport clip rect */
 
-            PolygonSink *polygon_sink = nullptr;
-
             static constexpr double dbg_fill_alpha = 0.8;
             static constexpr double dbg_stroke_alpha = 1.0;
             static constexpr double assumed_usvg_dpi = 96.0;
diff --git a/svg-flatten/src/main.cpp b/svg-flatten/src/main.cpp
index bacfa71..54ce896 100644
--- a/svg-flatten/src/main.cpp
+++ b/svg-flatten/src/main.cpp
@@ -377,7 +377,7 @@ int main(int argc, char **argv) {
         return EXIT_FAILURE;
     }
 
-    doc.render(rset, *top_sink, &sel);
+    doc.render(rset, *top_sink, sel);
 
     remove(frob.c_str());
     remove(barf.c_str());
diff --git a/svg-flatten/src/out_scaler.cpp b/svg-flatten/src/out_scaler.cpp
index 983dffe..9b7de4e 100644
--- a/svg-flatten/src/out_scaler.cpp
+++ b/svg-flatten/src/out_scaler.cpp
@@ -29,27 +29,27 @@
 using namespace gerbolyze;
 using namespace std;
 
-void Scaler::header(d2p origin, d2p size) {
+void PolygonScaler::header(d2p origin, d2p size) {
     m_sink.header({origin[0] * m_scale, origin[1] * m_scale}, {size[0] * m_scale, size[1] * m_scale});
 }
 
-void Scaler::footer() {
+void PolygonScaler::footer() {
     m_sink.footer();
 }
 
-Scaler &Scaler::operator<<(const LayerNameToken &layer_name) {
+PolygonScaler &PolygonScaler::operator<<(const LayerNameToken &layer_name) {
     m_sink << layer_name;
 
     return *this;
 }
 
-Scaler &Scaler::operator<<(GerberPolarityToken pol) {
+PolygonScaler &PolygonScaler::operator<<(GerberPolarityToken pol) {
     m_sink << pol;
 
     return *this;
 }
 
-Scaler &Scaler::operator<<(const Polygon &poly) {
+PolygonScaler &PolygonScaler::operator<<(const Polygon &poly) {
     Polygon new_poly;
     for (auto &p : poly) {
         new_poly.push_back({ p[0] * m_scale, p[1] * m_scale });
diff --git a/svg-flatten/src/out_sexp.cpp b/svg-flatten/src/out_sexp.cpp
index 9a04416..1a7f1d0 100644
--- a/svg-flatten/src/out_sexp.cpp
+++ b/svg-flatten/src/out_sexp.cpp
@@ -29,6 +29,40 @@ using namespace gerbolyze;
 using namespace std;
 
 
+/* Note: These values come from KiCAD's common/lset.cpp. KiCAD uses *multiple different names* for the same layer in
+ * different places, and not all of them are stable. Sometimes, these names change without notice. If this list isn't
+ * up-to-date, it's not my fault. Still, please file an issue. */
+const std::vector<std::string> gerbolyze::kicad_default_layers ({
+        /* Copper */
+        "F.Cu",
+        "In1.Cu", "In2.Cu", "In3.Cu", "In4.Cu", "In5.Cu", "In6.Cu", "In7.Cu", "In8.Cu",
+        "In9.Cu", "In10.Cu", "In11.Cu", "In12.Cu", "In13.Cu", "In14.Cu", "In15.Cu", "In16.Cu",
+        "In17.Cu", "In18.Cu", "In19.Cu", "In20.Cu", "In21.Cu", "In22.Cu", "In23.Cu",
+        "In24.Cu", "In25.Cu", "In26.Cu", "In27.Cu", "In28.Cu", "In29.Cu", "In30.Cu",
+        "B.Cu",
+
+        /* Technical layers */
+        "B.Adhes", "F.Adhes",
+        "B.Paste", "F.Paste",
+        "B.SilkS", "F.SilkS",
+        "B.Mask", "F.Mask",
+
+        /* User layers */
+        "Dwgs.User",
+        "Cmts.User",
+        "Eco1.User", "Eco2.User",
+        "Edge.Cuts",
+        "Margin",
+
+        /* Footprint layers */
+        "F.CrtYd", "B.CrtYd",
+        "F.Fab", "B.Fab",
+
+        /* Layers for user scripting etc. */
+        "User.1", "User.2", "User.3", "User.4", "User.5", "User.6", "User.7", "User.8", "User.9",
+    });
+
+
 KicadSexpOutput::KicadSexpOutput(ostream &out, string mod_name, string layer, bool only_polys, string ref_text, string val_text, d2p ref_pos, d2p val_pos)
     : StreamPolygonSink(out, only_polys),
     m_mod_name(mod_name),
@@ -105,4 +139,3 @@ void KicadSexpOutput::footer_impl() {
     m_out << ")" << endl;
 }
 
-
diff --git a/svg-flatten/src/svg_doc.cpp b/svg-flatten/src/svg_doc.cpp
index 639d7fa..d90e00d 100644
--- a/svg-flatten/src/svg_doc.cpp
+++ b/svg-flatten/src/svg_doc.cpp
@@ -132,14 +132,7 @@ bool IDElementSelector::match(const pugi::xml_node &node, bool included, bool is
 }
 
 /* Recursively export all SVG elements in the given group. */
-void gerbolyze::SVGDocument::export_svg_group(xform2d &mat, const RenderSettings &rset, const pugi::xml_node &group, Paths &parent_clip_path, const ElementSelector *sel, bool included, bool is_root) {
-
-    /* Load clip paths from defs given bezier flattening tolerance from rset */
-    load_clips(rset);
-    
-    /* Enter the group's coordinate system */
-    xform2d local_xf(mat);
-    local_xf.transform(xform2d(group.attribute("transform").value()));
+void gerbolyze::SVGDocument::export_svg_group(RenderContext &ctx, const pugi::xml_node &group) {
 
     /* Fetch clip path from global registry and transform it into document coordinates. */
     Paths clip_path;
@@ -152,50 +145,56 @@ void gerbolyze::SVGDocument::export_svg_group(xform2d &mat, const RenderSettings
 
     } else {
         clip_path = *lookup;
-        local_xf.transform_paths(clip_path);
+        ctx.mat().transform_paths(clip_path);
     }
 
     /* Clip against parent's clip path (both are now in document coordinates) */
-    if (!parent_clip_path.empty()) {
+    if (!ctx.clip().empty()) {
         if (!clip_path.empty()) {
-            combine_clip_paths(parent_clip_path, clip_path, clip_path);
+            Clipper c;
+            c.StrictlySimple(true);
+            c.AddPaths(ctx.clip(), ptClip, /* closed */ true);
+            c.AddPaths(clip_path, ptSubject, /* closed */ true);
+            /* Nonzero fill since both input clip paths must already have been preprocessed by clipper. */
+            c.Execute(ctIntersection, clip_path, pftNonZero);
         } else {
-            clip_path = parent_clip_path;
+            clip_path = ctx.clip();
         }
     }
 
     /* Iterate over the group's children, exporting them one by one. */
     for (const auto &node : group.children()) {
-        if (sel && !sel->match(node, included, is_root))
+        if (!ctx.match(node))
             continue;
 
         string name(node.name());
+        RenderContext elem_ctx(ctx, xform2d(node.attribute("transform").value()), clip_path);
         if (name == "g") {
-            if (is_root) { /* Treat top-level groups as "layers" like inkscape does. */
+            if (ctx.root()) { /* Treat top-level groups as "layers" like inkscape does. */
                 cerr << "Forwarding layer name to sink: \"" << node.attribute("id").value() << "\"" << endl;
                 LayerNameToken tok { node.attribute("id").value() };
-                *polygon_sink << tok;
+                elem_ctx.sink() << tok;
             }
 
-            export_svg_group(local_xf, rset, node, clip_path, sel, true);
+            export_svg_group(elem_ctx, node);
             
-            if (is_root) {
+            if (ctx.root()) {
                 LayerNameToken tok {""};
-                *polygon_sink << tok;
+                elem_ctx.sink() << tok;
             }
 
         } else if (name == "path") {
-            export_svg_path(local_xf, rset, node, clip_path);
+            export_svg_path(elem_ctx, node);
 
         } else if (name == "image") {
-            ImageVectorizer *vec = rset.m_vec_sel.select(node);
+            ImageVectorizer *vec = ctx.settings().m_vec_sel.select(node);
             if (!vec) {
                 cerr << "Cannot resolve vectorizer for node \"" << node.attribute("id").value() << "\"" << endl;
                 continue;
             }
 
-            double min_feature_size_px = mm_to_doc_units(rset.m_minimum_feature_size_mm);
-            vec->vectorize_image(local_xf, node, clip_path, *polygon_sink, min_feature_size_px);
+            double min_feature_size_px = mm_to_doc_units(ctx.settings().m_minimum_feature_size_mm);
+            vec->vectorize_image(elem_ctx, node, min_feature_size_px);
             delete vec;
 
         } else if (name == "defs") {
@@ -207,9 +206,9 @@ void gerbolyze::SVGDocument::export_svg_group(xform2d &mat, const RenderSettings
 }
 
 /* Export an SVG path element to gerber. Apply patterns and clip on the fly. */
-void gerbolyze::SVGDocument::export_svg_path(xform2d &mat, const RenderSettings &rset, const pugi::xml_node &node, Paths &clip_path) {
-    enum gerber_color fill_color = gerber_fill_color(node, rset);
-    enum gerber_color stroke_color = gerber_stroke_color(node, rset);
+void gerbolyze::SVGDocument::export_svg_path(RenderContext &ctx, const pugi::xml_node &node) {
+    enum gerber_color fill_color = gerber_fill_color(node, ctx.settings());
+    enum gerber_color stroke_color = gerber_stroke_color(node, ctx.settings());
 
     double stroke_width = usvg_double_attr(node, "stroke-width", /* default */ 1.0);
     assert(stroke_width > 0.0);
@@ -225,15 +224,13 @@ void gerbolyze::SVGDocument::export_svg_path(xform2d &mat, const RenderSettings
     }
 
     /* Load path from SVG path data and transform into document units. */
-    xform2d local_xf(mat);
-    local_xf.transform(xform2d(node.attribute("transform").value()));
     /* FIXME transform stroke width here? */
-    stroke_width = local_xf.doc2phys_dist(stroke_width);
+    stroke_width = ctx.mat().doc2phys_dist(stroke_width);
 
     Paths stroke_open, stroke_closed;
     PolyTree ptree_fill;
     PolyTree ptree;
-    load_svg_path(local_xf, node, stroke_open, stroke_closed, ptree_fill, rset.curve_tolerance_mm);
+    load_svg_path(ctx.mat(), node, stroke_open, stroke_closed, ptree_fill, ctx.settings().curve_tolerance_mm);
 
     Paths fill_paths;
     PolyTreeToPaths(ptree_fill, fill_paths);
@@ -243,17 +240,16 @@ void gerbolyze::SVGDocument::export_svg_path(xform2d &mat, const RenderSettings
 
     /* Skip filling for transparent fills. In outline mode, skip filling if a stroke is also set to avoid double lines.
      */
-    if (fill_color && !(rset.outline_mode && has_stroke)) {
+    if (has_fill && !(ctx.settings().outline_mode && has_stroke)) {
         /* Clip paths. Consider all paths closed for filling. */
-        if (!clip_path.empty()) {
+        if (!ctx.clip().empty()) {
             Clipper c;
             c.AddPaths(fill_paths, ptSubject, /* closed */ true);
-            c.AddPaths(clip_path, ptClip, /* closed */ true);
+            c.AddPaths(ctx.clip(), 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_fill, pftNonZero, pftNonZero);
-            PolyTreeToPaths(ptree_fill, fill_paths);
         }
 
         /* Call out to pattern tiler for pattern fills. The path becomes the clip here. */
@@ -264,11 +260,13 @@ void gerbolyze::SVGDocument::export_svg_path(xform2d &mat, const RenderSettings
                 cerr << "Warning: Fill pattern with id \"" << fill_pattern_id << "\" not found." << endl;
 
             } else {
-                pattern->tile(local_xf, rset, fill_paths);
+                PolyTreeToPaths(ptree_fill, fill_paths);
+                RenderContext local_ctx(ctx, xform2d(), fill_paths);
+                pattern->tile(local_ctx);
             }
 
         } else { /* solid fill */
-            if (rset.outline_mode) {
+            if (ctx.settings().outline_mode) {
                 fill_color = GRB_DARK;
             }
 
@@ -286,10 +284,10 @@ void gerbolyze::SVGDocument::export_svg_path(xform2d &mat, const RenderSettings
                             });
 
                 /* In outline mode, manually close polys */
-                if (rset.outline_mode && !out.empty())
+                if (ctx.settings().outline_mode && !out.empty())
                     out.push_back(out[0]);
 
-                *polygon_sink << (fill_color == GRB_DARK ? GRB_POL_DARK : GRB_POL_CLEAR) << out;
+                ctx.sink() << (fill_color == GRB_DARK ? GRB_POL_DARK : GRB_POL_CLEAR) << out;
             }
         }
     }
@@ -307,10 +305,10 @@ void gerbolyze::SVGDocument::export_svg_path(xform2d &mat, const RenderSettings
             /* Special case: A closed path becomes a number of open paths when it is dashed. */
             if (dasharray.empty()) {
 
-                if (rset.outline_mode && stroke_color != GRB_PATTERN_FILL) {
+                if (ctx.settings().outline_mode && stroke_color != GRB_PATTERN_FILL) {
                     /* In outline mode, manually close polys */
                     poly.push_back(poly[0]);
-                    *polygon_sink << ApertureToken() << poly;
+                    ctx.sink() << ApertureToken() << poly;
 
                 } else {
                     offx.AddPath(poly, join_type, etClosedLine);
@@ -322,8 +320,8 @@ void gerbolyze::SVGDocument::export_svg_path(xform2d &mat, const RenderSettings
                 Paths out;
                 dash_path(poly_copy, out, dasharray, stroke_dashoffset);
 
-                if (rset.outline_mode && stroke_color != GRB_PATTERN_FILL) {
-                    *polygon_sink << ApertureToken(stroke_width) << out;
+                if (ctx.settings().outline_mode && stroke_color != GRB_PATTERN_FILL) {
+                    ctx.sink() << ApertureToken(stroke_width) << out;
                 } else {
                     offx.AddPaths(out, join_type, end_type);
                 }
@@ -334,8 +332,8 @@ void gerbolyze::SVGDocument::export_svg_path(xform2d &mat, const RenderSettings
             Paths out;
             dash_path(poly, out, dasharray, stroke_dashoffset);
 
-            if (rset.outline_mode && stroke_color != GRB_PATTERN_FILL) {
-                *polygon_sink << ApertureToken(stroke_width) << out;
+            if (ctx.settings().outline_mode && stroke_color != GRB_PATTERN_FILL) {
+                ctx.sink() << ApertureToken(stroke_width) << out;
             } else {
                 offx.AddPaths(out, join_type, end_type);
             }
@@ -346,13 +344,13 @@ void gerbolyze::SVGDocument::export_svg_path(xform2d &mat, const RenderSettings
 
         /* 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()) {
+        if (!ctx.clip().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.AddPaths(ctx.clip(), 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);
@@ -368,20 +366,21 @@ void gerbolyze::SVGDocument::export_svg_path(xform2d &mat, const RenderSettings
             } else {
                 Paths clip;
                 PolyTreeToPaths(ptree, clip);
-                pattern->tile(local_xf, rset, clip);
+                RenderContext local_ctx(ctx, xform2d(), clip);
+                pattern->tile(local_ctx);
             }
 
-        } else if (!rset.outline_mode) {
+        } else if (!ctx.settings().outline_mode) {
             Paths s_polys;
             dehole_polytree(ptree, s_polys);
 
-            *polygon_sink << ApertureToken() << (stroke_color == GRB_DARK ? GRB_POL_DARK : GRB_POL_CLEAR) << s_polys;
+            ctx.sink() << ApertureToken() << (stroke_color == GRB_DARK ? GRB_POL_DARK : GRB_POL_CLEAR) << s_polys;
         }
     }
-    *polygon_sink << ApertureToken();
+    ctx.sink() << ApertureToken();
 }
 
-void gerbolyze::SVGDocument::render(const RenderSettings &rset, PolygonSink &sink, const ElementSelector *sel) {
+void gerbolyze::SVGDocument::render(const RenderSettings &rset, PolygonSink &sink, const ElementSelector &sel) {
     assert(_valid);
     /* Export the actual SVG document. 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
@@ -389,21 +388,18 @@ void gerbolyze::SVGDocument::render(const RenderSettings &rset, PolygonSink &sin
      */
 
     /* Scale document pixels to mm for sinks */
-    Scaler scaler(sink, doc_units_to_mm(1.0));
+    PolygonScaler scaler(sink, doc_units_to_mm(1.0));
+    RenderContext ctx(rset, scaler, sel, vb_paths);
+
+    /* Load clip paths from defs with given bezier flattening tolerance and unit scale */
+    load_clips(rset);
 
-    polygon_sink = &scaler;
     scaler.header({vb_x, vb_y}, {vb_w, vb_h});
-    ClipperLib::Clipper c;
-    c.AddPaths(vb_paths, ptSubject, /* closed */ true);
-    ClipperLib::IntRect bbox = c.GetBounds();
-    cerr << "document viewbox clip: bbox={" << bbox.left << ", " << bbox.top << "} - {" << bbox.right << ", " << bbox.bottom << "}" << endl;
-    xform2d xf;
-    export_svg_group(xf, rset, root_elem, vb_paths, sel, false, true);
+    export_svg_group(ctx, root_elem);
     scaler.footer();
-    polygon_sink = nullptr;
 }
 
-void gerbolyze::SVGDocument::render_to_list(const RenderSettings &rset, vector<pair<Polygon, GerberPolarityToken>> &out, const ElementSelector *sel) {
+void gerbolyze::SVGDocument::render_to_list(const RenderSettings &rset, vector<pair<Polygon, GerberPolarityToken>> &out, const ElementSelector &sel) {
     LambdaPolygonSink sink([&out](const Polygon &poly, GerberPolarityToken pol) {
             out.emplace_back(pair<Polygon, GerberPolarityToken>{poly, pol});
         });
@@ -413,14 +409,14 @@ void gerbolyze::SVGDocument::render_to_list(const RenderSettings &rset, vector<p
 void gerbolyze::SVGDocument::setup_viewport_clip() {
     /* Set up view port clip path */
     Path vb_path;
-    for (auto &elem : vector<pair<double, double>> {{vb_x, vb_y}, {vb_x+vb_w, vb_y}, {vb_x+vb_w, vb_y+vb_h}, {vb_x, vb_y+vb_h}}) {
-        double x = elem.first, y = elem.second;
-        vb_path.push_back({ (cInt)round(x * clipper_scale), (cInt)round(y * clipper_scale) });
+    for (d2p &p : vector<d2p> {
+            {vb_x,      vb_y},
+            {vb_x+vb_w, vb_y},
+            {vb_x+vb_w, vb_y+vb_h},
+            {vb_x,      vb_y+vb_h}}) {
+        vb_path.push_back({ (cInt)round(p[0] * clipper_scale), (cInt)round(p[1] * clipper_scale) });
     }
     vb_paths.push_back(vb_path);
-
-    ClipperLib::Clipper c;
-    c.AddPaths(vb_paths, ptSubject, /* closed */ true);
 }
 
 void gerbolyze::SVGDocument::load_patterns() {
@@ -478,35 +474,35 @@ void gerbolyze::SVGDocument::load_clips(const RenderSettings &rset) {
     }
 }
 
-/* Note: These values come from KiCAD's common/lset.cpp. KiCAD uses *multiple different names* for the same layer in
- * different places, and not all of them are stable. Sometimes, these names change without notice. If this list isn't
- * up-to-date, it's not my fault. Still, please file an issue. */
-const std::vector<std::string> gerbolyze::kicad_default_layers ({
-        /* Copper */
-        "F.Cu",
-        "In1.Cu", "In2.Cu", "In3.Cu", "In4.Cu", "In5.Cu", "In6.Cu", "In7.Cu", "In8.Cu",
-        "In9.Cu", "In10.Cu", "In11.Cu", "In12.Cu", "In13.Cu", "In14.Cu", "In15.Cu", "In16.Cu",
-        "In17.Cu", "In18.Cu", "In19.Cu", "In20.Cu", "In21.Cu", "In22.Cu", "In23.Cu",
-        "In24.Cu", "In25.Cu", "In26.Cu", "In27.Cu", "In28.Cu", "In29.Cu", "In30.Cu",
-        "B.Cu",
-
-        /* Technical layers */
-        "B.Adhes", "F.Adhes",
-        "B.Paste", "F.Paste",
-        "B.SilkS", "F.SilkS",
-        "B.Mask", "F.Mask",
-
-        /* User layers */
-        "Dwgs.User",
-        "Cmts.User",
-        "Eco1.User", "Eco2.User",
-        "Edge.Cuts",
-        "Margin",
-
-        /* Footprint layers */
-        "F.CrtYd", "B.CrtYd",
-        "F.Fab", "B.Fab",
-
-        /* Layers for user scripting etc. */
-        "User.1", "User.2", "User.3", "User.4", "User.5", "User.6", "User.7", "User.8", "User.9",
-        });
+
+gerbolyze::RenderContext::RenderContext(const RenderSettings &settings,
+        PolygonSink &sink,
+        const ElementSelector &sel,
+        ClipperLib::Paths &clip) :
+    m_sink(sink),
+    m_settings(settings),
+    m_mat(),
+    m_root(true),
+    m_included(false),
+    m_sel(sel),
+    m_clip(clip)
+{
+}
+
+gerbolyze::RenderContext::RenderContext(RenderContext &parent, xform2d transform) :
+    RenderContext(parent, transform, parent.clip())
+{
+}
+
+gerbolyze::RenderContext::RenderContext(RenderContext &parent, xform2d transform, ClipperLib::Paths &clip) :
+    m_sink(parent.sink()),
+    m_settings(parent.settings()),
+    m_mat(parent.mat()),
+    m_root(false),
+    m_included(parent.included()),
+    m_sel(parent.sel()),
+    m_clip(clip)
+{
+    m_mat.transform(transform);
+}
+
diff --git a/svg-flatten/src/svg_geom.cpp b/svg-flatten/src/svg_geom.cpp
index f836567..a36c881 100644
--- a/svg-flatten/src/svg_geom.cpp
+++ b/svg-flatten/src/svg_geom.cpp
@@ -147,14 +147,3 @@ void gerbolyze::dehole_polytree(PolyTree &ptree, Paths &out) {
     }
 }
 
-
-/* Intersect two clip paths. Both must share a coordinate system. */
-void gerbolyze::combine_clip_paths(Paths &in_a, Paths &in_b, Paths &out) {
-    Clipper c;
-    c.StrictlySimple(true);
-    c.AddPaths(in_a, ptClip, /* closed */ true);
-    c.AddPaths(in_b, ptSubject, /* closed */ true);
-    /* Nonzero fill since both input clip paths must already have been preprocessed by clipper. */
-    c.Execute(ctIntersection, out, pftNonZero);
-}
-
diff --git a/svg-flatten/src/svg_pattern.cpp b/svg-flatten/src/svg_pattern.cpp
index cbdf4dd..b68bf3a 100644
--- a/svg-flatten/src/svg_pattern.cpp
+++ b/svg-flatten/src/svg_pattern.cpp
@@ -54,17 +54,17 @@ gerbolyze::Pattern::Pattern(const pugi::xml_node &node, SVGDocument &doc) : _nod
 
 /* Tile pattern into gerber. Note that this function may be called several times in case the pattern is
  * referenced from multiple places, so we must not clobber any of the object's state. */
-void gerbolyze::Pattern::tile (xform2d &mat, const gerbolyze::RenderSettings &rset, ClipperLib::Paths &clip) {
+void gerbolyze::Pattern::tile (gerbolyze::RenderContext &ctx) {
     assert(doc);
 
     /* 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 */
-    d2p pos_xf = mat.doc2phys(d2p{x, y});
+    d2p pos_xf = ctx.mat().doc2phys(d2p{x, y});
     double inst_x = pos_xf[0], inst_y = pos_xf[1];
-    double inst_w = mat.doc2phys_dist(w);
-    double inst_h = mat.doc2phys_dist(h);
+    double inst_w = ctx.mat().doc2phys_dist(w);
+    double inst_h = ctx.mat().doc2phys_dist(h);
 
-    ClipperLib::IntRect clip_bounds = get_paths_bounds(clip);
+    ClipperLib::IntRect clip_bounds = get_paths_bounds(ctx.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;
@@ -86,8 +86,7 @@ void gerbolyze::Pattern::tile (xform2d &mat, const gerbolyze::RenderSettings &rs
     }
 
     /* Switch to pattern coordinates */
-    xform2d local_xf(mat);
-    local_xf.transform(patternTransform);
+    RenderContext pat_ctx(ctx, patternTransform);
 
     /* Iterate over all pattern tiles in pattern coordinates */
     for (double inst_off_x = fmod(inst_x, inst_w) - 2*inst_w;
@@ -98,7 +97,7 @@ void gerbolyze::Pattern::tile (xform2d &mat, const gerbolyze::RenderSettings &rs
                 inst_off_y < bh + 2*inst_h;
                 inst_off_y += inst_h) {
 
-            xform2d elem_xf(local_xf);
+            xform2d elem_xf;
             /* Change into this individual tile's coordinate system */
             elem_xf.translate(inst_off_x, inst_off_y);
             if (has_vb) {
@@ -109,7 +108,8 @@ void gerbolyze::Pattern::tile (xform2d &mat, const gerbolyze::RenderSettings &rs
             }
 
             /* Export the pattern tile's content like a group */
-            doc->export_svg_group(elem_xf, rset, _node, clip);
+            RenderContext elem_ctx(pat_ctx, elem_xf);
+            doc->export_svg_group(elem_ctx, _node);
         }
     }
 }
diff --git a/svg-flatten/src/svg_pattern.h b/svg-flatten/src/svg_pattern.h
index 56444dd..73efe5a 100644
--- a/svg-flatten/src/svg_pattern.h
+++ b/svg-flatten/src/svg_pattern.h
@@ -30,13 +30,14 @@ namespace gerbolyze {
 
 class SVGDocument;
 class RenderSettings;
+class RenderContext;
 
 class Pattern {
 public:
     Pattern() {}
     Pattern(const pugi::xml_node &node, SVGDocument &doc);
 
-    void tile (xform2d &mat, const gerbolyze::RenderSettings &rset, ClipperLib::Paths &clip);
+    void tile (RenderContext &ctx);
 
 private:
     double x, y, w, h;
diff --git a/svg-flatten/src/vec_core.cpp b/svg-flatten/src/vec_core.cpp
index 86641dd..1b36887 100644
--- a/svg-flatten/src/vec_core.cpp
+++ b/svg-flatten/src/vec_core.cpp
@@ -95,15 +95,19 @@ template<typename T> nopencv::Image<T> *img_from_node(const pugi::xml_node &node
     return img;
 }
 
-void gerbolyze::draw_bg_rect(xform2d &mat, double width, double height, ClipperLib::Paths &clip_path, PolygonSink &sink) {
+void gerbolyze::draw_bg_rect(RenderContext &ctx, double width, double height) {
     /* For our output to look correct, 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.
      *
      * 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}}) {
-        d2p xf(mat.doc2phys(d2p{elem.first, elem.second}));
+    for (auto &elem : vector<pair<double, double>> {
+            {0,     0},
+            {width, 0},
+            {width, height},
+            {0,     height}}) {
+        d2p xf(ctx.mat().doc2phys(d2p{elem.first, elem.second}));
         rect_path.push_back({
                 (ClipperLib::cInt)round(xf[0] * clipper_scale),
                 (ClipperLib::cInt)round(xf[1] * clipper_scale)
@@ -113,8 +117,8 @@ void gerbolyze::draw_bg_rect(xform2d &mat, double width, double height, ClipperL
     /* 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);
+    if (!ctx.clip().empty()) {
+        c.AddPaths(ctx.clip(), ClipperLib::ptClip, /* closed */ true);
     }
 
     ClipperLib::Paths rect_out;
@@ -128,7 +132,7 @@ void gerbolyze::draw_bg_rect(xform2d &mat, double width, double height, ClipperL
             out.push_back(std::array<double, 2>{
                     ((double)p.X) / clipper_scale, ((double)p.Y) / clipper_scale
                     });
-        sink << GRB_POL_CLEAR << out;
+        ctx.sink() << GRB_POL_CLEAR << out;
     }
 }
 
@@ -152,7 +156,7 @@ void gerbolyze::draw_bg_rect(xform2d &mat, double width, double height, ClipperL
  * 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(xform2d &mat, const pugi::xml_node &node, ClipperLib::Paths &clip_path, PolygonSink &sink, double min_feature_size_px) {
+void gerbolyze::VoronoiVectorizer::vectorize_image(RenderContext &ctx, const pugi::xml_node &node, double min_feature_size_px) {
     double x, y, width, height;
     parse_img_meta(node, x, y, width, height);
     nopencv::Image32f *img = img_from_node<float>(node);
@@ -160,10 +164,8 @@ void gerbolyze::VoronoiVectorizer::vectorize_image(xform2d &mat, const pugi::xml
         return;
 
     /* Set up target transform using SVG transform and x/y attributes */
-    xform2d local_xf(mat);
-    local_xf.transform(xform2d(node.attribute("transform").value()));
-    local_xf.translate(x, y);
-    cerr << "voronoi vectorizer: local_xf = " << local_xf.dbg_str() << endl;
+    RenderContext img_ctx(ctx, xform2d(1, 0, 0, 1, x, y));
+    cerr << "voronoi vectorizer: local_xf = " << ctx.mat().dbg_str() << endl;
 
     double orig_rows = img->rows();
     double orig_cols = img->cols();
@@ -176,10 +178,10 @@ void gerbolyze::VoronoiVectorizer::vectorize_image(xform2d &mat, const pugi::xml
     cerr << "aspect " << scale_x << ", " << scale_y << " / " << off_x << ", " << off_y << endl;
 
     /* Adjust minimum feature size given in mm and translate into px document units in our local coordinate system. */
-    min_feature_size_px = local_xf.doc2phys_dist(min_feature_size_px);
+    min_feature_size_px = img_ctx.mat().doc2phys_dist(min_feature_size_px);
     cerr << "  min_feature_size_px = " << min_feature_size_px << endl;
 
-    draw_bg_rect(local_xf, width, height, clip_path, sink);
+    draw_bg_rect(img_ctx, width, height);
 
     /* Set up a poisson-disc sampled point "grid" covering the image. Calculate poisson disc parameters from given
      * minimum feature size. */
@@ -306,7 +308,7 @@ void gerbolyze::VoronoiVectorizer::vectorize_image(xform2d &mat, const pugi::xml
             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". */
-                d2p p = local_xf.doc2phys(d2p{
+                d2p p = img_ctx.mat().doc2phys(d2p{
                     off_x + center.x + (e->pos[0].x - center.x) * fill_factor,
                     off_y + center.y + (e->pos[0].y - center.y) * fill_factor
                 });
@@ -318,7 +320,7 @@ void gerbolyze::VoronoiVectorizer::vectorize_image(xform2d &mat, const pugi::xml
             }
 
             /* Emit endpoint of current edge */
-            d2p p = local_xf.doc2phys(d2p{
+            d2p p = img_ctx.mat().doc2phys(d2p{
                 off_x + center.x + (e->pos[1].x - center.x) * fill_factor,
                 off_y + center.y + (e->pos[1].y - center.y) * fill_factor
             });
@@ -339,8 +341,8 @@ void gerbolyze::VoronoiVectorizer::vectorize_image(xform2d &mat, const pugi::xml
         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);
+        if (!img_ctx.clip().empty()) {
+            c.AddPaths(img_ctx.clip(), ClipperLib::ptClip, /* closed */ true);
         }
         c.StrictlySimple(true);
         c.Execute(ClipperLib::ctIntersection, polys, ClipperLib::pftNonZero, ClipperLib::pftNonZero);
@@ -352,7 +354,7 @@ void gerbolyze::VoronoiVectorizer::vectorize_image(xform2d &mat, const pugi::xml
                 out.push_back(std::array<double, 2>{
                         ((double)p.X) / clipper_scale, ((double)p.Y) / clipper_scale
                         });
-            sink << GRB_POL_DARK << out;
+            img_ctx.sink() << GRB_POL_DARK << out;
         }
     }
 
@@ -413,7 +415,7 @@ void gerbolyze::handle_aspect_ratio(string spec, double &scale_x, double &scale_
 }
 
 
-void gerbolyze::OpenCVContoursVectorizer::vectorize_image(xform2d &mat, const pugi::xml_node &node, ClipperLib::Paths &clip_path, PolygonSink &sink, double min_feature_size_px) {
+void gerbolyze::OpenCVContoursVectorizer::vectorize_image(RenderContext &ctx, const pugi::xml_node &node, double min_feature_size_px) {
     (void) min_feature_size_px; /* unused by this vectorizer */
     double x, y, width, height;
     parse_img_meta(node, x, y, width, height);
@@ -422,9 +424,7 @@ void gerbolyze::OpenCVContoursVectorizer::vectorize_image(xform2d &mat, const pu
         return;
 
     /* Set up target transform using SVG transform and x/y attributes */
-    xform2d local_xf(mat);
-    local_xf.transform(xform2d(node.attribute("transform").value()));
-    local_xf.translate(x, y);
+    RenderContext img_ctx(ctx, xform2d(1, 0, 0, 1, x, y));
 
     double scale_x = (double)width / (double)img->cols();
     double scale_y = (double)height / (double)img->rows();
@@ -433,24 +433,24 @@ void gerbolyze::OpenCVContoursVectorizer::vectorize_image(xform2d &mat, const pu
     handle_aspect_ratio(node.attribute("preserveAspectRatio").value(),
             scale_x, scale_y, off_x, off_y, img->cols(), img->rows());
 
-    draw_bg_rect(local_xf, width, height, clip_path, sink);
+    draw_bg_rect(img_ctx, width, height);
 
     img->binarize(128);
     nopencv::find_contours(*img,
             nopencv::simplify_contours_douglas_peucker(
-                [&sink, &local_xf, &clip_path, off_x, off_y, scale_x, scale_y](Polygon_i& poly, nopencv::ContourPolarity pol) {
+                [&img_ctx, off_x, off_y, scale_x, scale_y](Polygon_i& poly, nopencv::ContourPolarity pol) {
 
         if (pol == nopencv::CP_HOLE) {
             std::reverse(poly.begin(), poly.end());
-            sink << GRB_POL_CLEAR;
+            img_ctx.sink() << GRB_POL_CLEAR;
 
         } else {
-            sink << GRB_POL_DARK;
+            img_ctx.sink() << GRB_POL_DARK;
         }
 
         ClipperLib::Path out;
         for (const auto &p : poly) {
-            d2p q = local_xf.doc2phys(d2p{
+            d2p q = img_ctx.mat().doc2phys(d2p{
                 off_x + (double)p[0] * scale_x,
                 off_y + (double)p[1] * scale_y
             });
@@ -462,8 +462,8 @@ void gerbolyze::OpenCVContoursVectorizer::vectorize_image(xform2d &mat, const pu
 
         ClipperLib::Clipper c;
         c.AddPath(out, ClipperLib::ptSubject, /* closed */ true);
-        if (!clip_path.empty()) {
-            c.AddPaths(clip_path, ClipperLib::ptClip, /* closed */ true);
+        if (!img_ctx.clip().empty()) {
+            c.AddPaths(img_ctx.clip(), ClipperLib::ptClip, /* closed */ true);
         }
         c.StrictlySimple(true);
         ClipperLib::Paths polys;
@@ -476,7 +476,7 @@ void gerbolyze::OpenCVContoursVectorizer::vectorize_image(xform2d &mat, const pu
                 out.push_back(std::array<double, 2>{
                         ((double)p.X) / clipper_scale, ((double)p.Y) / clipper_scale
                         });
-            sink << out;
+            img_ctx.sink() << out;
         }
     }));
 }
diff --git a/svg-flatten/src/vec_core.h b/svg-flatten/src/vec_core.h
index ce25807..024d98f 100644
--- a/svg-flatten/src/vec_core.h
+++ b/svg-flatten/src/vec_core.h
@@ -29,7 +29,7 @@ namespace gerbolyze {
     public:
         VoronoiVectorizer(grid_type grid, bool relax=true) : m_relax(relax), m_grid_type(grid) {}
 
-        virtual void vectorize_image(xform2d &mat, const pugi::xml_node &node, ClipperLib::Paths &clip_path, PolygonSink &sink, double min_feature_size_px);
+        virtual void vectorize_image(RenderContext &ctx, const pugi::xml_node &node, double min_feature_size_px);
     private:
         double m_relax;
         grid_type m_grid_type;
@@ -39,18 +39,18 @@ namespace gerbolyze {
     public:
         OpenCVContoursVectorizer() {}
 
-        virtual void vectorize_image(xform2d &mat, const pugi::xml_node &node, ClipperLib::Paths &clip_path, PolygonSink &sink, double min_feature_size_px);
+        virtual void vectorize_image(RenderContext &ctx, const pugi::xml_node &node, double min_feature_size_px);
     };
 
     class DevNullVectorizer : public ImageVectorizer {
     public:
         DevNullVectorizer() {}
 
-        virtual void vectorize_image(xform2d &, const pugi::xml_node &, ClipperLib::Paths &, PolygonSink &, double) {}
+        virtual void vectorize_image(RenderContext &, const pugi::xml_node &, double) {}
     };
 
     void parse_img_meta(const pugi::xml_node &node, double &x, double &y, double &width, double &height);
-    void draw_bg_rect(xform2d &mat, double width, double height, ClipperLib::Paths &clip_path, PolygonSink &sink);
+    void draw_bg_rect(RenderContext &ctx, double width, double height);
     void handle_aspect_ratio(std::string spec, double &scale_x, double &scale_y, double &off_x, double &off_y, double cols, double rows);
 }