Address review feedback

* Add counts to offsets when comparing against buffer size limits
* Remove multiplication by 4 in blend buffer allocation (we use units of u32)
* Move buffer sizes from BumpAllocators to Config
* Add comments about early exit

shader/binning.wgsl

@@ -128,7 +128,7 @@ fn main(
     }
     // element_count is the number of draw objects covering this thread's bin
     var chunk_offset = atomicAdd(&bump.binning, element_count);
-    if chunk_offset > bump.binning_size {
+    if chunk_offset + element_count > config.binning_size {
         chunk_offset = 0u;
         atomicOr(&bump.failed, STAGE_BINNING);
     }    

shader/coarse.wgsl

@@ -71,7 +71,7 @@ fn alloc_cmd(size: u32) {
         // by setting the initial value of the bump allocator.
         let ptcl_dyn_start = config.width_in_tiles * config.height_in_tiles * PTCL_INITIAL_ALLOC;
         var new_cmd = ptcl_dyn_start + atomicAdd(&bump.ptcl, PTCL_INCREMENT);
-        if new_cmd > bump.ptcl_size {
+        if new_cmd + PTCL_INCREMENT > config.ptcl_size {
             new_cmd = 0u;
             atomicOr(&bump.failed, STAGE_COARSE);
         }
@@ -137,7 +137,7 @@ fn write_end_clip(end_clip: CmdEndClip) {
     ptcl[cmd_offset] = CMD_END_CLIP;
     ptcl[cmd_offset + 1u] = end_clip.blend;
     ptcl[cmd_offset + 2u] = bitcast<u32>(end_clip.alpha);
-    cmd_offset += 3u;            
+    cmd_offset += 3u;
 }
 
 @compute @workgroup_size(256)
@@ -145,9 +145,12 @@ fn main(
     @builtin(local_invocation_id) local_id: vec3<u32>,
     @builtin(workgroup_id) wg_id: vec3<u32>,
 ) {
+    // Exit early if prior stages failed, as we can't run this stage.
+    // We need to check only prior stages, as if this stage has failed in another workgroup, 
+    // we still want to know this workgroup's memory requirement.   
     if (atomicLoad(&bump.failed) & (STAGE_BINNING | STAGE_TILE_ALLOC | STAGE_PATH_COARSE)) != 0u {
         return;
-    }     
+    }
     let width_in_bins = (config.width_in_tiles + N_TILE_X - 1u) / N_TILE_X;
     let bin_ix = width_in_bins * wg_id.y + wg_id.x;
     let n_partitions = (config.n_drawobj + N_TILE - 1u) / N_TILE;
@@ -411,7 +414,7 @@ fn main(
     if bin_tile_x + tile_x < config.width_in_tiles && bin_tile_y + tile_y < config.height_in_tiles {
         ptcl[cmd_offset] = CMD_END;
         if max_blend_depth > BLEND_STACK_SPLIT {
-            let scratch_size = max_blend_depth * TILE_WIDTH * TILE_HEIGHT * 4u;
+            let scratch_size = max_blend_depth * TILE_WIDTH * TILE_HEIGHT;
             ptcl[blend_offset] = atomicAdd(&bump.blend, scratch_size);
         }
     }

shader/path_coarse_full.wgsl

@@ -94,7 +94,7 @@ fn eval_cubic(p0: vec2<f32>, p1: vec2<f32>, p2: vec2<f32>, p3: vec2<f32>, t: f32
 
 fn alloc_segment() -> u32 {
     var offset = atomicAdd(&bump.segments, 1u) + 1u;
-    if offset > bump.segments_size {
+    if offset + 1u > config.segments_size {
         offset = 0u;
         atomicOr(&bump.failed, STAGE_PATH_COARSE);
     }
@@ -107,6 +107,9 @@ let MAX_QUADS = 16u;
 fn main(
     @builtin(global_invocation_id) global_id: vec3<u32>,
 ) {
+    // Exit early if prior stages failed, as we can't run this stage.
+    // We need to check only prior stages, as if this stage has failed in another workgroup, 
+    // we still want to know this workgroup's memory requirement.   
     if (atomicLoad(&bump.failed) & (STAGE_BINNING | STAGE_TILE_ALLOC)) != 0u {
         return;
     }

shader/shared/bump.wgsl

@@ -10,10 +10,6 @@ let STAGE_COARSE: u32 = 0x8u;
 struct BumpAllocators {
     // Bitmask of stages that have failed allocation.
     failed: atomic<u32>,
-    binning_size: u32,
-    ptcl_size: u32,
-    tiles_size: u32,
-    segments_size: u32,
     binning: atomic<u32>,
     ptcl: atomic<u32>,
     tile: atomic<u32>,

shader/shared/config.wgsl

@@ -24,6 +24,12 @@ struct Config {
 
     transform_base: u32,
     linewidth_base: u32,
+
+    // Sizes of bump allocated buffers (in element size units)
+    binning_size: u32,
+    tiles_size: u32,
+    segments_size: u32,    
+    ptcl_size: u32,
 }
 
 // Geometry of tiles and bins

shader/tile_alloc.wgsl

@@ -35,6 +35,9 @@ fn main(
     @builtin(global_invocation_id) global_id: vec3<u32>,
     @builtin(local_invocation_id) local_id: vec3<u32>,
 ) {
+    // Exit early if prior stages failed, as we can't run this stage.
+    // We need to check only prior stages, as if this stage has failed in another workgroup, 
+    // we still want to know this workgroup's memory requirement.   
     if (atomicLoad(&bump.failed) & STAGE_BINNING) != 0u {
         return;
     }    
@@ -75,8 +78,9 @@ fn main(
         sh_tile_count[local_id.x] = total_tile_count;
     }
     if local_id.x == WG_SIZE - 1u {
-        var offset = atomicAdd(&bump.tile, sh_tile_count[WG_SIZE - 1u]);
-        if offset > bump.tiles_size {
+        let count = sh_tile_count[WG_SIZE - 1u];
+        var offset = atomicAdd(&bump.tile, count);
+        if offset + count > config.tiles_size {
             offset = 0u;
             atomicOr(&bump.failed, STAGE_TILE_ALLOC);
         }

src/encoding/packed.rs

@@ -62,6 +62,14 @@ pub struct Config {
     pub target_height: u32,
     /// Layout of packed scene data.
     pub layout: Layout,
+    /// Size of binning buffer allocation (in u32s).
+    pub binning_size: u32,
+    /// Size of tile buffer allocation (in Tiles).
+    pub tiles_size: u32,
+    /// Size of segment buffer allocation (in PathSegments).
+    pub segments_size: u32,
+    /// Size of per-tile command list buffer allocation (in u32s).
+    pub ptcl_size: u32,
 }
 
 /// Packed encoding of scene data.

src/render.rs

@@ -61,11 +61,6 @@ pub const fn next_multiple_of(val: u32, rhs: u32) -> u32 {
 #[derive(Clone, Copy, Debug, Default, Zeroable, Pod)]
 struct BumpAllocators {
     failed: u32,
-    // Sizes of the provided buffers
-    binning_size: u32,
-    ptcl_size: u32,
-    tiles_size: u32,
-    segments_size: u32,
     // Final needed dynamic size of the buffers. If any of these are larger than the corresponding `_size` element
     // reallocation needs to occur
     binning: u32,
@@ -195,33 +190,30 @@ pub fn render_encoding_full(
     let new_width = next_multiple_of(width, 16);
     let new_height = next_multiple_of(height, 16);
 
+    let info_size = packed.layout.bin_data_start;
     let config = crate::encoding::Config {
         width_in_tiles: new_width / 16,
         height_in_tiles: new_height / 16,
         target_width: width,
         target_height: height,
+        binning_size: ((1 << 20) / 4) - info_size,
+        tiles_size: (1 << 24) / TILE_SIZE as u32,
+        segments_size: (1 << 26) / SEGMENT_SIZE as u32,
+        ptcl_size: (1 << 25) / 4,
         layout: packed.layout,
     };
     // println!("{:?}", config);
     let scene_buf = ResourceProxy::Buf(recording.upload("scene", packed.data));
     let config_buf =
         ResourceProxy::Buf(recording.upload_uniform("config", bytemuck::bytes_of(&config)));
-    let info_size = config.layout.bin_data_start;
-    let bump = BumpAllocators {
-        binning_size: ((1 << 20) / 4) - info_size,
-        ptcl_size: (1 << 25) / 4,
-        tiles_size: (1 << 24) / TILE_SIZE as u32,
-        segments_size: (1 << 26) / SEGMENT_SIZE as u32,
-        ..Default::default()
-    };
     let info_bin_data_buf = ResourceProxy::new_buf(
-        (info_size + bump.binning_size) as u64 * 4,
+        (info_size + config.binning_size) as u64 * 4,
         "info_bin_data_buf",
     );
-    let tile_buf = ResourceProxy::new_buf(bump.tiles_size as u64 * TILE_SIZE, "tile_buf");
+    let tile_buf = ResourceProxy::new_buf(config.tiles_size as u64 * TILE_SIZE, "tile_buf");
     let segments_buf =
-        ResourceProxy::new_buf(bump.segments_size as u64 * SEGMENT_SIZE, "segments_buf");
-    let ptcl_buf = ResourceProxy::new_buf(bump.ptcl_size as u64 * 4, "ptcl_buf");
+        ResourceProxy::new_buf(config.segments_size as u64 * SEGMENT_SIZE, "segments_buf");
+    let ptcl_buf = ResourceProxy::new_buf(config.ptcl_size as u64 * 4, "ptcl_buf");
 
     let pathtag_wgs = pathtag_padded / (4 * shaders::PATHTAG_REDUCE_WG as usize);
     let pathtag_large = pathtag_wgs > shaders::PATHTAG_REDUCE_WG as usize;
@@ -356,13 +348,14 @@ pub fn render_encoding_full(
         );
     }
     let draw_bbox_buf = ResourceProxy::new_buf(n_paths as u64 * DRAW_BBOX_SIZE, "draw_bbox_buf");
-    let bump_buf = recording.upload("bump_buf", bytemuck::bytes_of(&bump));
+    let bump_buf = BufProxy::new(BUMP_SIZE, "bump_buf");
     let width_in_bins = (config.width_in_tiles + 15) / 16;
     let height_in_bins = (config.height_in_tiles + 15) / 16;
     let bin_header_buf = ResourceProxy::new_buf(
         (256 * drawobj_wgs) as u64 * BIN_HEADER_SIZE,
         "bin_header_buf",
     );
+    recording.clear_all(bump_buf);
     let bump_buf = ResourceProxy::Buf(bump_buf);
     recording.dispatch(
         shaders.binning,