Merge pull request #242 from linebender/evenodd

Support even-odd fill rule

examples/with_winit/src/test_scene.rs

@@ -271,7 +271,16 @@ fn blend_square(blend: BlendMode) -> SceneFragment {
 
 #[allow(unused)]
 pub fn render_anim_frame(sb: &mut SceneBuilder, text: &mut SimpleText, i: usize) {
+    use PathEl::*;
     let rect = Rect::from_origin_size(Point::new(0.0, 0.0), (1000.0, 1000.0));
+    let star = [
+        MoveTo((50.0, 0.0).into()),
+        LineTo((21.0, 90.0).into()),
+        LineTo((98.0, 35.0).into()),
+        LineTo((2.0, 35.0).into()),
+        LineTo((79.0, 90.0).into()),
+        ClosePath,
+    ];
     sb.fill(
         Fill::NonZero,
         Affine::IDENTITY,
@@ -333,6 +342,20 @@ pub fn render_anim_frame(sb: &mut SceneBuilder, text: &mut SimpleText, i: usize)
         &rect,
     );
     sb.pop_layer();
+    sb.fill(
+        Fill::NonZero,
+        Affine::translate((400.0, 100.0)),
+        Color::PURPLE,
+        None,
+        &star,
+    );
+    sb.fill(
+        Fill::EvenOdd,
+        Affine::translate((500.0, 100.0)),
+        Color::PURPLE,
+        None,
+        &star,
+    );
 }
 
 #[allow(unused)]

shader/coarse.wgsl

@@ -79,17 +79,22 @@ fn alloc_cmd(size: u32) {
     }
 }
 
-fn write_path(tile: Tile, linewidth: f32) {
+fn write_path(tile: Tile, linewidth: f32) -> bool {
     // TODO: take flags
     alloc_cmd(3u);
     if linewidth < 0.0 {
+        let even_odd = linewidth < -1.0;
         if tile.segments != 0u {
             let fill = CmdFill(tile.segments, tile.backdrop);
             ptcl[cmd_offset] = CMD_FILL;
-            ptcl[cmd_offset + 1u] = fill.tile;
+            let segments_and_rule = select(fill.tile << 1u, (fill.tile << 1u) | 1u, even_odd);
+            ptcl[cmd_offset + 1u] = segments_and_rule;
             ptcl[cmd_offset + 2u] = u32(fill.backdrop);
             cmd_offset += 3u;
         } else {
+            if even_odd && (abs(tile.backdrop) & 1) == 0 {
+                return false;
+            }
             ptcl[cmd_offset] = CMD_SOLID;
             cmd_offset += 1u;
         }
@@ -100,6 +105,7 @@ fn write_path(tile: Tile, linewidth: f32) {
         ptcl[cmd_offset + 2u] = bitcast<u32>(stroke.half_width);
         cmd_offset += 3u;
     }
+    return true;
 }
 
 fn write_color(color: CmdColor) {
@@ -323,26 +329,29 @@ fn main(
                     // DRAWTAG_FILL_COLOR
                     case 0x44u: {
                         let linewidth = bitcast<f32>(info_bin_data[di]);
-                        write_path(tile, linewidth);
+                        if write_path(tile, linewidth) {
                             let rgba_color = scene[dd];
                             write_color(CmdColor(rgba_color));
                         }
+                    }
                     // DRAWTAG_FILL_LIN_GRADIENT
                     case 0x114u: {
                         let linewidth = bitcast<f32>(info_bin_data[di]);
-                        write_path(tile, linewidth);
+                        if write_path(tile, linewidth) {
                             let index = scene[dd];
                             let info_offset = di + 1u;
                             write_grad(CMD_LIN_GRAD, index, info_offset);
                         }
+                    }
                     // DRAWTAG_FILL_RAD_GRADIENT
                     case 0x2dcu: {
                         let linewidth = bitcast<f32>(info_bin_data[di]);
-                        write_path(tile, linewidth);
+                        if write_path(tile, linewidth) {
                             let index = scene[dd];
                             let info_offset = di + 1u;
                             write_grad(CMD_RAD_GRAD, index, info_offset);
                         }
+                    }
                     // DRAWTAG_BEGIN_CLIP
                     case 0x9u: {
                         if tile.segments == 0u && tile.backdrop == 0 {

shader/fine.wgsl

@@ -97,7 +97,7 @@ var output: texture_storage_2d<r8, write>;
 
 let PIXELS_PER_THREAD = 4u;
 
-fn fill_path(tile: Tile, xy: vec2<f32>) -> array<f32, PIXELS_PER_THREAD> {
+fn fill_path(tile: Tile, xy: vec2<f32>, even_odd: bool) -> array<f32, PIXELS_PER_THREAD> {
     var area: array<f32, PIXELS_PER_THREAD>;
     let backdrop_f = f32(tile.backdrop);
     for (var i = 0u; i < PIXELS_PER_THREAD; i += 1u) {
@@ -136,10 +136,18 @@ fn fill_path(tile: Tile, xy: vec2<f32>) -> array<f32, PIXELS_PER_THREAD> {
         }
         segment_ix = segment.next;
     }
-    // nonzero winding rule
+    if even_odd {
+        // even-odd winding rule
+        for (var i = 0u; i < PIXELS_PER_THREAD; i += 1u) {
+            let a = abs(area[i]);
+            area[i] = select(a, 2.0 - min(a, 2.0), a > 1.0);
+        }
+    } else {
+        // non-zero winding rule
         for (var i = 0u; i < PIXELS_PER_THREAD; i += 1u) {
             area[i] = min(abs(area[i]), 1.0);
         }
+    }
     return area;
 }
 
@@ -195,8 +203,10 @@ fn main(
             // CMD_FILL
             case 1u: {
                 let fill = read_fill(cmd_ix);
-                let tile = Tile(fill.backdrop, fill.tile);
+                let segments = fill.tile >> 1u;
-                area = fill_path(tile, xy);
+                let even_odd = (fill.tile & 1u) != 0u;
+                let tile = Tile(fill.backdrop, segments);
+                area = fill_path(tile, xy, even_odd);
                 cmd_ix += 3u;
             }
             // CMD_STROKE

src/scene.rs

@@ -126,7 +126,7 @@ impl<'a> SceneBuilder<'a> {
     /// Fills a shape using the specified style and brush.
     pub fn fill<'b>(
         &mut self,
-        _style: Fill,
+        style: Fill,
         transform: Affine,
         brush: impl Into<BrushRef<'b>>,
         brush_transform: Option<Affine>,
@@ -134,7 +134,10 @@ impl<'a> SceneBuilder<'a> {
     ) {
         self.scene
             .encode_transform(Transform::from_kurbo(&transform));
-        self.scene.encode_linewidth(-1.0);
+        self.scene.encode_linewidth(match style {
+            Fill::NonZero => -1.0,
+            Fill::EvenOdd => -2.0,
+        });
         if self.scene.encode_shape(shape, true) {
             if let Some(brush_transform) = brush_transform {
                 self.scene