WebGPUBackend - Cannot use Compute Indirect Unless Buffer is in Compute Function.

[cmhhelgeson]

Related issue: #31488

Description

Passing only an indirect buffer without accessing the buffer in a compute function produces this error.

Likely because this code in WebGPUBackend.js doesn't have a fallback condition when dispatchBuffer returns undefined.

Although indirect compute is most useful when the number of workgroups is defined by the GPU, I think for the sake of correctness we should still be able to create a minimum viable example where the indirect buffer is used without being modified.

// Line 1381 - 1389 of Renderer.js

if ( dispatchSize && typeof dispatchSize === 'object' && dispatchSize.isIndirectStorageBufferAttribute ) {
	const dispatchBuffer = this.get( dispatchSize ).buffer;
	passEncoderGPU.dispatchWorkgroupsIndirect( dispatchBuffer, 0 );
	return;
}

Reproduction steps

1. On webgpu_compute_particles rain, at the top of the file, create an IndirectStorageBufferAttribute with the requisite number of workgroups to calculate the initial number of renderer rain particles.

const maxParticleCount = 50000;
const workgroupSize = 64;
const instanceCount = maxParticleCount / 2;
const startNumWorkgroups = Math.ceil( instanceCount / workgroupSize );

const workgroupGridIndirectBuffer = new THREE.IndirectStorageBufferAttribute( new Uint32Array( [ startNumWorkgroups, 1, 1 ]), 1 );

2. Modify computeParticles to account for the fact that the dispatchSize will be determined by a combination of the workgroupSize and the indirectBuffer rather than the count.

// count not taken into consideration when buffer is indirect
computeParticles = computeUpdate().compute( null, [ 64, 1, 1 ] ).setName( 'Particles' );

3. Modify the computeParticles call in the animation loop.

renderer.compute( computeParticles, workgroupGridIndirectBuffer );

Code

Seen above.

Live example

WebGPU Example

Screenshots

No response

Version

r181

Device

Desktop

Browser

Chrome

OS

Windows

[Spiri0]

I don't know if I'll have time to look at it next week. I'll try.