Allow large numbers of draw objects

Previously there was a limit of workgroup size squared for the number of draw objects, which is 64k in practice. This PR makes each workgroup iterate multiple blocks if that limit is exceeded, borrowing a technique from FidelityFX sort.

WIP, this causes hangs on mac. Uploading to test on other hardware.

Also contains some changes for testing that may not want to be committed as is.

Fixes #334

crates/encoding/src/config.rs

@@ -234,6 +234,7 @@ impl WorkgroupCounts {
             path_tag_wgs
         };
         let draw_object_wgs = (n_draw_objects + PATH_BBOX_WG - 1) / PATH_BBOX_WG;
+        let draw_monoid_wgs = draw_object_wgs.min(PATH_BBOX_WG);
         let flatten_wgs = (n_path_tags + FLATTEN_WG - 1) / FLATTEN_WG;
         let clip_reduce_wgs = n_clips.saturating_sub(1) / CLIP_REDUCE_WG;
         let clip_wgs = (n_clips + CLIP_REDUCE_WG - 1) / CLIP_REDUCE_WG;
@@ -248,8 +249,8 @@ impl WorkgroupCounts {
             path_scan: (path_tag_wgs, 1, 1),
             bbox_clear: (draw_object_wgs, 1, 1),
             flatten: (flatten_wgs, 1, 1),
-            draw_reduce: (draw_object_wgs, 1, 1),
-            draw_leaf: (draw_object_wgs, 1, 1),
+            draw_reduce: (draw_monoid_wgs, 1, 1),
+            draw_leaf: (draw_monoid_wgs, 1, 1),
             clip_reduce: (clip_reduce_wgs, 1, 1),
             clip_leaf: (clip_wgs, 1, 1),
             binning: (draw_object_wgs, 1, 1),
@@ -364,8 +365,9 @@ impl BufferSizes {
         let path_reduced_scan = BufferSize::new(path_tag_wgs);
         let path_monoids = BufferSize::new(path_tag_wgs * PATH_REDUCE_WG);
         let path_bboxes = BufferSize::new(n_paths);
-        let draw_object_wgs = workgroups.draw_reduce.0;
-        let draw_reduced = BufferSize::new(draw_object_wgs);
+        let binning_wgs = workgroups.binning.0;
+        let draw_monoid_wgs = workgroups.draw_reduce.0;
+        let draw_reduced = BufferSize::new(draw_monoid_wgs);
         let draw_monoids = BufferSize::new(n_draw_objects);
         let info = BufferSize::new(layout.bin_data_start);
         let clip_inps = BufferSize::new(n_clips);
@@ -375,7 +377,7 @@ impl BufferSizes {
         let draw_bboxes = BufferSize::new(n_paths);
         let bump_alloc = BufferSize::new(1);
         let indirect_count = BufferSize::new(1);
-        let bin_headers = BufferSize::new(draw_object_wgs * 256);
+        let bin_headers = BufferSize::new(binning_wgs * 256);
         let n_paths_aligned = align_up(n_paths, 256);
         let paths = BufferSize::new(n_paths_aligned);
 

examples/scenes/src/test_scenes.rs

@@ -2,7 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
 use crate::{ExampleScene, SceneConfig, SceneParams, SceneSet};
-use vello::kurbo::{Affine, BezPath, Cap, Ellipse, Join, PathEl, Point, Rect, Shape, Stroke, Vec2};
+use vello::kurbo::{
+    Affine, BezPath, Cap, Circle, Ellipse, Join, PathEl, Point, Rect, Shape, Stroke, Vec2,
+};
 use vello::peniko::*;
 use vello::*;
 
@@ -31,6 +33,7 @@ macro_rules! scene {
 
 pub fn test_scenes() -> SceneSet {
     let scenes = vec![
+        scene!(many_draw),
         scene!(splash_with_tiger(), "splash_with_tiger", false),
         scene!(funky_paths),
         scene!(stroke_styles(Affine::IDENTITY), "stroke_styles", false),
@@ -67,6 +70,21 @@ pub fn test_scenes() -> SceneSet {
 
 // Scenes
 
+fn many_draw(scene: &mut Scene, _: &mut SceneParams) {
+    const N_WIDE: usize = 300;
+    const N_HIGH: usize = 300;
+    const SCENE_WIDTH: f64 = 2000.0;
+    const SCENE_HEIGHT: f64 = 1500.0;
+    for j in 0..N_HIGH {
+        let y = (j as f64 + 0.5) * (SCENE_HEIGHT / N_HIGH as f64);
+        for i in 0..N_WIDE {
+            let x = (i as f64 + 0.5) * (SCENE_WIDTH / N_WIDE as f64);
+            let c = Circle::new((x, y), 3.0);
+            scene.fill(Fill::NonZero, Affine::IDENTITY, Color::YELLOW, None, &c);
+        }
+    }
+}
+
 fn funky_paths(scene: &mut Scene, _: &mut SceneParams) {
     use PathEl::*;
     let missing_movetos = [