Transition all pipelines to new draw_flags field for fill rule

crates/encoding/src/draw.rs

@@ -41,6 +41,11 @@ impl DrawTag {
     }
 }
 
+/// The first word of each draw info stream entry contains the flags. This is not part of the
+/// draw object stream but gets used after the draw objects get reduced on the GPU.
+/// 0 represents a non-zero fill. 1 represents an even-odd fill.
+pub const DRAW_INFO_FLAGS_FILL_RULE_BIT: u32 = 1;
+
 /// Draw object bounding box.
 #[derive(Copy, Clone, Pod, Zeroable, Debug, Default)]
 #[repr(C)]

crates/encoding/src/lib.rs

@@ -29,7 +29,7 @@ pub use config::{
 };
 pub use draw::{
     DrawBbox, DrawBeginClip, DrawColor, DrawImage, DrawLinearGradient, DrawMonoid,
-    DrawRadialGradient, DrawTag,
+    DrawRadialGradient, DrawTag, DRAW_INFO_FLAGS_FILL_RULE_BIT,
 };
 pub use encoding::{Encoding, StreamOffsets};
 pub use math::Transform;

crates/encoding/src/path.rs

@@ -380,8 +380,8 @@ pub struct PathBbox {
     pub x1: i32,
     /// Maximum y value.
     pub y1: i32,
-    /// Line width.
-    pub linewidth: f32,
+    /// Style flags
+    pub draw_flags: u32,
     /// Index into the transform stream.
     pub trans_ix: u32,
 }

examples/scenes/src/test_scenes.rs

@@ -324,7 +324,43 @@ fn fill_types(sb: &mut SceneBuilder, params: &mut SceneParams) {
         sb.fill(
             rule.0,
             Affine::translate((0., 10.)) * t,
-            Color::BLACK,
+            Color::YELLOW,
+            None,
+            &rule.2,
+        );
+    }
+
+    // Draw blends
+    let t = Affine::translate((700., 0.)) * t;
+    for (i, rule) in rules.iter().enumerate() {
+        let t = Affine::translate(((i % 2) as f64 * 306., (i / 2) as f64 * 340.)) * t;
+        params.text.add(sb, None, 24., None, t, rule.1);
+        let t = Affine::translate((0., 5.)) * t * scale;
+        sb.fill(
+            Fill::NonZero,
+            t,
+            &Brush::Solid(Color::rgb8(128, 128, 128)),
+            None,
+            &rect,
+        );
+        sb.fill(
+            rule.0,
+            Affine::translate((0., 10.)) * t,
+            Color::YELLOW,
+            None,
+            &rule.2,
+        );
+        sb.fill(
+            rule.0,
+            Affine::translate((0., 10.)) * t * Affine::rotate(0.06),
+            Color::rgba(0., 1., 0.7, 0.6),
+            None,
+            &rule.2,
+        );
+        sb.fill(
+            rule.0,
+            Affine::translate((0., 10.)) * t * Affine::rotate(-0.06),
+            Color::rgba(0.9, 0.7, 0.5, 0.6),
             None,
             &rule.2,
         );
@@ -373,7 +409,7 @@ fn longpathdash(cap: Cap) -> impl FnMut(&mut SceneBuilder, &mut SceneParams) {
         sb.stroke(
             &Stroke::new(1.0).with_caps(cap).with_dashes(0.0, [1.0, 1.0]),
             Affine::translate((50.0, 50.0)),
-            Color::rgb8(255, 255, 0),
+            Color::YELLOW,
             None,
             &path,
         );

shader/bbox_clear.wgsl

@@ -1,19 +1,11 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT OR Unlicense
 
 #import config
+#import bbox
 
 @group(0) @binding(0)
 var<uniform> config: Config;
 
-struct PathBbox {
-    x0: i32,
-    y0: i32,
-    x1: i32,
-    y1: i32,
-    linewidth: f32,
-    trans_ix: u32,
-}
-
 @group(0) @binding(1)
 var<storage, read_write> path_bboxes: array<PathBbox>;
 

shader/coarse.wgsl

@@ -82,8 +82,7 @@ fn alloc_cmd(size: u32) {
     }
 }
 
-fn write_path(tile: Tile, tile_ix: u32, linewidth: f32) -> bool {
-    let even_odd = linewidth < -1.0;
+fn write_path(tile: Tile, tile_ix: u32, draw_flags: u32) {
     // We overload the "segments" field to store both count (written by
     // path_count stage) and segment allocation (used by path_tiling and
     // fine).
@@ -93,21 +92,18 @@ fn write_path(tile: Tile, tile_ix: u32, linewidth: f32) -> bool {
         tiles[tile_ix].segment_count_or_ix = ~seg_ix;
         alloc_cmd(4u);
         ptcl[cmd_offset] = CMD_FILL;
+        let even_odd = (draw_flags & DRAW_INFO_FLAGS_FILL_RULE_BIT) != 0u;
         let size_and_rule = (n_segs << 1u) | u32(even_odd);
         let fill = CmdFill(size_and_rule, seg_ix, tile.backdrop);
         ptcl[cmd_offset + 1u] = fill.size_and_rule;
         ptcl[cmd_offset + 2u] = fill.seg_data;
         ptcl[cmd_offset + 3u] = u32(fill.backdrop);
         cmd_offset += 4u;
     } else {
-        if even_odd && (abs(tile.backdrop) & 1) == 0 {
-            return false;
-        }
         alloc_cmd(1u);
         ptcl[cmd_offset] = CMD_SOLID;
         cmd_offset += 1u;
     }
-    return true;
 }
 
 fn write_color(color: CmdColor) {
@@ -310,7 +306,17 @@ fn main(
                 let blend = scene[dd];
                 is_blend = blend != BLEND_CLIP;
             }
-            let include_tile = tile.segment_count_or_ix != 0u || (tile.backdrop == 0) == is_clip || is_blend;
+
+            let di = draw_monoids[drawobj_ix].info_offset;
+            let draw_flags = info_bin_data[di];
+            let even_odd = (draw_flags & DRAW_INFO_FLAGS_FILL_RULE_BIT) != 0u;
+            let n_segs = tile.segment_count_or_ix;
+
+            // If this draw object represents an even-odd fill and we know that no line segment
+            // crosses this tile and then this draw object should not contribute to the tile if its
+            // backdrop (i.e. the winding number of its top-left corner) is even.
+            let backdrop_clear = select(tile.backdrop, abs(tile.backdrop) & 1, even_odd) == 0;
+            let include_tile = n_segs != 0u || (backdrop_clear == is_clip) || is_blend;
             if include_tile {
                 let el_slice = el_ix / 32u;
                 let el_mask = 1u << (el_ix & 31u);
@@ -336,6 +342,7 @@ fn main(
                     continue;
                 }
             }
+
             let el_ix = slice_ix * 32u + firstTrailingBit(bitmap);
             drawobj_ix = sh_drawobj_ix[el_ix];
             // clear LSB of bitmap, using bit magic
@@ -344,42 +351,35 @@ fn main(
             let dm = draw_monoids[drawobj_ix];
             let dd = config.drawdata_base + dm.scene_offset;
             let di = dm.info_offset;
+            let draw_flags = info_bin_data[di];
             if clip_zero_depth == 0u {
                 let tile_ix = sh_tile_base[el_ix] + sh_tile_stride[el_ix] * tile_y + tile_x;
                 let tile = tiles[tile_ix];
                 switch drawtag {
                     // DRAWTAG_FILL_COLOR
                     case 0x44u: {
-                        let linewidth = bitcast<f32>(info_bin_data[di]);
-                        if write_path(tile, tile_ix, linewidth) {
-                            let rgba_color = scene[dd];
-                            write_color(CmdColor(rgba_color));
-                        }
+                        write_path(tile, tile_ix, draw_flags);
+                        let rgba_color = scene[dd];
+                        write_color(CmdColor(rgba_color));
                     }
                     // DRAWTAG_FILL_LIN_GRADIENT
                     case 0x114u: {
-                        let linewidth = bitcast<f32>(info_bin_data[di]);
-                        if write_path(tile, tile_ix, linewidth) {
-                            let index = scene[dd];
-                            let info_offset = di + 1u;
-                            write_grad(CMD_LIN_GRAD, index, info_offset);
-                        }
+                        write_path(tile, tile_ix, draw_flags);
+                        let index = scene[dd];
+                        let info_offset = di + 1u;
+                        write_grad(CMD_LIN_GRAD, index, info_offset);
                     }
                     // DRAWTAG_FILL_RAD_GRADIENT
                     case 0x29cu: {
-                        let linewidth = bitcast<f32>(info_bin_data[di]);
-                        if write_path(tile, tile_ix, linewidth) {
-                            let index = scene[dd];
-                            let info_offset = di + 1u;
-                            write_grad(CMD_RAD_GRAD, index, info_offset);
-                        }
+                        write_path(tile, tile_ix, draw_flags);
+                        let index = scene[dd];
+                        let info_offset = di + 1u;
+                        write_grad(CMD_RAD_GRAD, index, info_offset);
                     }
                     // DRAWTAG_FILL_IMAGE
                     case 0x248u: {
-                        let linewidth = bitcast<f32>(info_bin_data[di]);
-                        if write_path(tile, tile_ix, linewidth) {
-                            write_image(di + 1u);
-                        }
+                        write_path(tile, tile_ix, draw_flags);
+                        write_image(di + 1u);
                     }
                     // DRAWTAG_BEGIN_CLIP
                     case 0x9u: {
@@ -395,7 +395,8 @@ fn main(
                     // DRAWTAG_END_CLIP
                     case 0x21u: {
                         clip_depth -= 1u;
-                        write_path(tile, tile_ix, -1.0);
+                        // A clip shape is always a non-zero fill (draw_flags=0).
+                        write_path(tile, tile_ix, /*draw_flags=*/0u);
                         let blend = scene[dd];
                         let alpha = bitcast<f32>(scene[dd + 1u]);
                         write_end_clip(CmdEndClip(blend, alpha));

shader/draw_leaf.wgsl

@@ -109,25 +109,20 @@ fn main(
         // let y1 = f32(bbox.y1);
         // let bbox_f = vec4(x0, y0, x1, y1);
         var transform = Transform();
-        var linewidth = bbox.linewidth;
-        if linewidth >= 0.0 || tag_word == DRAWTAG_FILL_LIN_GRADIENT || tag_word == DRAWTAG_FILL_RAD_GRADIENT ||
+        let draw_flags = bbox.draw_flags;
+        if tag_word == DRAWTAG_FILL_LIN_GRADIENT || tag_word == DRAWTAG_FILL_RAD_GRADIENT ||
             tag_word == DRAWTAG_FILL_IMAGE 
         {
             transform = read_transform(config.transform_base, bbox.trans_ix);
         }
-        if linewidth >= 0.0 {
-            // Note: doesn't deal with anisotropic case
-            let matrx = transform.matrx;
-            linewidth *= sqrt(abs(matrx.x * matrx.w - matrx.y * matrx.z));
-        }
         switch tag_word {
             // DRAWTAG_FILL_COLOR
             case 0x44u: {
-                info[di] = bitcast<u32>(linewidth);
+                info[di] = draw_flags;
             }
             // DRAWTAG_FILL_LIN_GRADIENT
             case 0x114u: {
-                info[di] = bitcast<u32>(linewidth);
+                info[di] = draw_flags;
                 var p0 = bitcast<vec2<f32>>(vec2(scene[dd + 1u], scene[dd + 2u]));
                 var p1 = bitcast<vec2<f32>>(vec2(scene[dd + 3u], scene[dd + 4u]));
                 p0 = transform_apply(transform, p0);
@@ -146,7 +141,7 @@ fn main(
                 // on the algorithm at <https://skia.org/docs/dev/design/conical/>
                 // This epsilon matches what Skia uses
                 let GRADIENT_EPSILON = 1.0 / f32(1 << 12u);
-                info[di] = bitcast<u32>(linewidth);
+                info[di] = draw_flags;
                 var p0 = bitcast<vec2<f32>>(vec2(scene[dd + 1u], scene[dd + 2u]));
                 var p1 = bitcast<vec2<f32>>(vec2(scene[dd + 3u], scene[dd + 4u]));
                 var r0 = bitcast<f32>(scene[dd + 5u]);
@@ -226,7 +221,7 @@ fn main(
             }
             // DRAWTAG_FILL_IMAGE
             case 0x248u: {
-                info[di] = bitcast<u32>(linewidth);
+                info[di] = draw_flags;
                 let inv = transform_inverse(transform);
                 info[di + 1u] = bitcast<u32>(inv.matrx.x);
                 info[di + 2u] = bitcast<u32>(inv.matrx.y);

shader/flatten.wgsl

@@ -3,6 +3,7 @@
 // Flatten curves to lines
 
 #import config
+#import drawtag
 #import pathtag
 #import segment
 #import cubic
@@ -22,7 +23,7 @@ struct AtomicPathBbox {
     y0: atomic<i32>,
     x1: atomic<i32>,
     y1: atomic<i32>,
-    linewidth: f32,
+    draw_flags: u32,
     trans_ix: u32,
 }
 
@@ -221,12 +222,9 @@ fn main(
     let style_flags = scene[config.style_base + tm.style_ix];
     // TODO: We assume all paths are fills at the moment. This is where we will extract the stroke
     // vs fill state using STYLE_FLAGS_STYLE_BIT.
-    // TODO: The downstream pipelines still use the old floating-point linewidth/fill encoding scheme
-    // This will change to represent the fill rule as a single bit inside the bounding box and draw
-    // info data structures.
-    let linewidth = select(-2.0, -1.0, (style_flags & STYLE_FLAGS_FILL_BIT) == 0u);
+    let draw_flags = select(DRAW_INFO_FLAGS_FILL_RULE_BIT, 0u, (style_flags & STYLE_FLAGS_FILL_BIT) == 0u);
     if (tag_byte & PATH_TAG_PATH) != 0u {
-        (*out).linewidth = linewidth;
+        (*out).draw_flags = draw_flags;
         (*out).trans_ix = tm.trans_ix;
     }
     // Decode path data
@@ -277,15 +275,18 @@ fn main(
             }
         }
         var stroke = vec2(0.0, 0.0);
-        if linewidth >= 0.0 {
+        let is_stroke = (style_flags & STYLE_FLAGS_STYLE_BIT) != 0u;
+        /*
+        // TODO: the stroke handling here is dead code for now
+        if is_stroke {
             // See https://www.iquilezles.org/www/articles/ellipses/ellipses.htm
             // This is the correct bounding box, but we're not handling rendering
             // in the isotropic case, so it may mismatch.
             stroke = 0.5 * linewidth * vec2(length(transform.mat.xz), length(transform.mat.yw));
             bbox += vec4(-stroke, stroke);
         }
-        let flags = u32(linewidth >= 0.0);
-        flatten_cubic(Cubic(p0, p1, p2, p3, stroke, tm.path_ix, flags));
+        */
+        flatten_cubic(Cubic(p0, p1, p2, p3, stroke, tm.path_ix, u32(is_stroke)));
         // Update bounding box using atomics only. Computing a monoid is a
         // potential future optimization.
         if bbox.z > bbox.x || bbox.w > bbox.y {

shader/shared/bbox.wgsl

@@ -4,12 +4,16 @@
 // but contains a link to the active transform, mostly for gradients.
 // Coordinates are integer pixels (for the convenience of atomic update)
 // but will probably become fixed-point fractions for rectangles.
+//
+// TODO: This also carries a `draw_flags` field that contains information that gets propagated to
+// the draw info stream. This is currently only used for the fill rule. If the other bits remain
+// unused we could possibly pack this into some other field, such as the the MSB of `trans_ix`.
 struct PathBbox {
     x0: i32,
     y0: i32,
     x1: i32,
     y1: i32,
-    linewidth: f32,
+    draw_flags: u32,
     trans_ix: u32,
 }
 

shader/shared/drawtag.wgsl

@@ -23,6 +23,11 @@ let DRAWTAG_FILL_IMAGE = 0x248u;
 let DRAWTAG_BEGIN_CLIP = 0x9u;
 let DRAWTAG_END_CLIP = 0x21u;
 
+/// The first word of each draw info stream entry contains the flags. This is not a part of the
+/// draw object stream but get used after the draw objects have been reduced on the GPU.
+/// 0 represents a non-zero fill. 1 represents an even-odd fill.
+let DRAW_INFO_FLAGS_FILL_RULE_BIT = 1u;
+
 fn draw_monoid_identity() -> DrawMonoid {
     return DrawMonoid();
 }