Bug 285402 – [WebGPU] https://playground.babylonjs.com/?webgpu#H1LRZ3#39 does not work in Safari Technology Preview

• Status: RESOLVED
• Resolution: DUPLICATE
• Component: WebGPU

[Mike Wyrzykowski]

https://playground.babylonjs.com/?webgpu#H1LRZ3#39 shows an empty canvas instead of the lines

[Mike Wyrzykowski]

Logging says Babylon.js is creating an invalid render pass but Chrome is allowing it

[Radar WebKit Bug Importer]

<rdar://problem/142382203>

[Mike Wyrzykowski]

I think WebKit is incorrect here, still investigating.

[Mike Wyrzykowski]

Created attachment 473787 [details]
disabled index buffer validation

Disabling index buffer validation in WebKit I see the attached image, either WebKit has a bug in the index validation or Babylon.js is attempting to draw out of bounds indices: 

See WebGPU specification note from https://www.w3.org/TR/webgpu/#dom-gpurendercommandsmixin-drawindexed
> NOTE: WebGPU applications should never use index data with indices out of bounds of any bound vertex buffer that has GPUVertexStepMode "vertex". WebGPU implementations have different ways of handling this, and therefore a range of behaviors is allowed. Either the whole draw call is discarded, or the access to those attributes out of bounds is described by WGSL’s invalid memory reference.

[Mike Wyrzykowski]

Created attachment 473788 [details]
OOB stage_in read

This seems to be duplicate of https://bugs.webkit.org/show_bug.cgi?id=285256

A 4 byte buffer is getting bound to slot 2, so we reject the draw call. Skipping validation shows an OOB read. 

The WebGPU spec allows both discarding the draw call or clamping. It appears Blink clamps while WebKit discards the draw.

[Mike Wyrzykowski]

This change to WebKit resolves both this issue and 285256. It is unclear why Babylon.js is creating 4 byte empty buffers when the shader appears to use them.

> diff --git a/Source/WebGPU/WebGPU/Buffer.mm b/Source/WebGPU/WebGPU/Buffer.mm
> index 43b708cc1be0..d72370580ab1 100644
> --- a/Source/WebGPU/WebGPU/Buffer.mm
> +++ b/Source/WebGPU/WebGPU/Buffer.mm
> @@ -113,6 +113,8 @@ static MTLStorageMode storageMode(bool deviceHasUnifiedMemory, WGPUBufferUsageFl
>  
>  id<MTLBuffer> Device::safeCreateBuffer(NSUInteger length, MTLStorageMode storageMode, MTLCPUCacheMode cpuCacheMode, MTLHazardTrackingMode hazardTrackingMode) const
>  {
> +    if (length == 4)
> +        length = 1024 * 64;
>      MTLResourceOptions resourceOptions = (cpuCacheMode << MTLResourceCPUCacheModeShift) | (storageMode << MTLResourceStorageModeShift) | (hazardTrackingMode << MTLResourceHazardTrackingModeShift);
>      id<MTLBuffer> buffer = [m_device newBufferWithLength:std::max<NSUInteger>(1, length) options:resourceOptions];
>      setOwnerWithIdentity(buffer);

[Mike Wyrzykowski]

*** This bug has been marked as a duplicate of bug 285256 ***