IOS app crash 0.2.1

[AngeloMateus]

IOS app crashes on launch with the following error:

-[MTLDebugComputeCommandEncoder dispatchThreadgroups:threadsPerThreadgroup:]:1054: failed assertion `(threadgroupsPerGrid.width(0) * threadgroupsPerGrid.y(1) * threadgroupsPerGrid.depth(1))(0) must not be 0.'

Previously tested working version: vello 0.1.0 (with bevy_vello 0.3.3)

Initially discussed here

Does anyone know how I can fix this?

[DJMcNab]

Thanks for the report.

There are a few things going on here:

1. We support iOS only on a best-effort basis.
2. That error suggests that one of the CPU side workgroup sizes is zero. These are set in

   vello/vello_encoding/src/config.rs

   Lines 250 to 269 in 984121d

   	Self {
   	use_large_path_scan,
   	path_reduce: (path_tag_wgs, 1, 1),
   	path_reduce2: (PATH_REDUCE_WG, 1, 1),
   	path_scan1: (reduced_size / PATH_REDUCE_WG, 1, 1),
   	path_scan: (path_tag_wgs, 1, 1),
   	bbox_clear: (draw_object_wgs, 1, 1),
   	flatten: (flatten_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),
   	tile_alloc: (path_wgs, 1, 1),
   	path_count_setup: (1, 1, 1),
   	backdrop: (path_wgs, 1, 1),
   	coarse: (width_in_bins, height_in_bins, 1),
   	path_tiling_setup: (1, 1, 1),
   	fine: (width_in_tiles, height_in_tiles, 1),
   	}

   . Can you please confirm which of those values has a first component of 0 for you?
3. The WebGPU spec requires that this case be supported. It is a bug in wgpu that this doesn't work. Can you please submit a minimal reproduction to them? This case should also be covered in the cts
4. We should be able to work around this ourselves, as dispatching a command doesn't have any observable side effects.
5. We might run into the same issue with indirect buffers. That will likely require a more involved workaround, or changing the WebGPU spec to not support this case.