Fix the validation for vertex limits for regular render passes (#5156)

CHANGELOG.md

@@ -76,6 +76,7 @@ Bottom level categories:
 #### General
 - Fix `panic!` when dropping `Instance` without `InstanceFlags::VALIDATION`. By @hakolao in [#5134](https://github.com/gfx-rs/wgpu/pull/5134)
 - Fix `serde` feature not compiling for `wgpu-types`. By @KirmesBude in [#5149](https://github.com/gfx-rs/wgpu/pull/5149)
+- Fix the validation of vertex and index ranges. By @nical in [#5144](https://github.com/gfx-rs/wgpu/pull/5144) and [#5156](https://github.com/gfx-rs/wgpu/pull/5156)
 
 #### WGL
 

wgpu-core/src/command/render.rs

@@ -378,18 +378,33 @@ struct VertexState {
 
 impl VertexState {
  fn update_limits(&mut self) {
- // TODO: This isn't entirely spec-compliant.
- // We currently require that the buffer range can fit `stride` * count bytes.
- // The spec, however, lets a buffer be a bit smaller as long as the size of the
- // last element fits in it (the last element can be smaller than the stride between
- // elements).
+ // Implements the validation from https://gpuweb.github.io/gpuweb/#dom-gpurendercommandsmixin-draw
+ // Except that the formula is shuffled to extract the number of vertices in order
+ // to carry the bulk of the computation when changing states intead of when producing
+ // draws. Draw calls tend to happen at a higher frequency. Here we determine vertex
+ // limits that can be cheaply checked for each draw call.
  self.vertex_limit = u32::MAX as u64;
  self.instance_limit = u32::MAX as u64;
  for (idx, vbs) in self.inputs.iter().enumerate() {
- if vbs.step.stride == 0 || !vbs.bound {
+ if !vbs.bound {
  continue;
  }
- let limit = vbs.total_size / vbs.step.stride;
+
+ let limit = if vbs.total_size < vbs.step.last_stride {
+ // The buffer cannot fit the last vertex.
+ 0
+ } else {
+ if vbs.step.stride == 0 {
+ // We already checked that the last stride fits, the same
+ // vertex will be repeated so this slot can accomodate any number of
+ // vertices.
+ continue;
+ }
+
+ // The general case.
+ (vbs.total_size - vbs.step.last_stride) / vbs.step.stride + 1
+ };
+
  match vbs.step.mode {
  VertexStepMode::Vertex => {
  if limit < self.vertex_limit {