expose `override` and `const` variables and their default value in `makeShaderDataDefinitions()` ?

[nraynaud]

Unless I'm mistaken, storing the compute shader workgroup size in a const or override variable is the only way to use it inside WGSL without resorting to copy/paste. Getting access to this value in JS is also a precious information to compute the dispatchWorkgroups() size.

example:

override workgroupxy_size = 8;

@group(0) @binding(0) var input_sampler: sampler;
@group(0) @binding(1) var input_texture: texture_2d<f32>;
@group(0) @binding(2) var output_texture: texture_storage_2d<rgba8unorm, write>;


@compute @workgroup_size(workgroupxy_size, workgroupxy_size, 1)
fn resize(@builtin(global_invocation_id) global_id: vec3<u32>) {
    let pixel_pos = global_id.xy;
    let texture_size = textureDimensions(output_texture);
    if all(pixel_pos < texture_size) {
        let texel = textureSampleLevel(input_texture, input_sampler, (vec2f(pixel_pos) + vec2f(0.5)) / vec2f(texture_size), 0);
        textureStore(output_texture, pixel_pos, texel);
    }
}

export async function loadWgsl (device, url, constants = {}) {
  const shaderCode = await (await fetch(url)).text()
  const defs = makeShaderDataDefinitions(shaderCode)
  console.log('DEF', defs)
  const module = device.createShaderModule({
    label: `${url} module`, code: shaderCode,
  })
  const pipelineDescs = objMap(defs.entryPoints, (key, _v) => ({
    label: `${key} pipeline`,
    layout: 'auto',
    compute: {module: module, entryPoint: key, constants: constants}
  }))
  const pipelines = objMap(pipelineDescs, (key, v) => {
    return device.createComputePipeline(v)
  })
  return {pipelines, defs, descriptors: pipelineDescs}
}


export async function  run() {
   (...)
    const wgSizeXY = 8
    const {pipelines, defs, descriptors} = await loadWgsl(device, 'resize.wgsl', {workgroupxy_size: wgSizeXY})
    const commandEncoder = device.createCommandEncoder()
    const computePass = commandEncoder.beginComputePass({label: 'image doubling compute pass'})
    await encodePipePrep(device, pipelines['resize'], computePass, {
      input_sampler: device.createSampler({magFilter: 'linear', minFilter: 'linear'}),
      input_texture: inputTexture.createView(),
      output_texture: outputTexture.createView()
    }, defs.entryPoints['resize'].resources)
    computePass.dispatchWorkgroups(Math.ceil(outputWidth / wgSizeXY), Math.ceil(outputHeight / wgSizeXY))
    (...)
}

receiving workgroupxy_size from the wgsl file would allow setting the value in the shader and using it in JS.