Motivation

Today GPUBindGroupLayout and GPUPipelineLayout are the most complicated part of the API. How about we add some defaults to them?

Namely it would change this sample code:

const bindGroupLayout = device.createBindGroupLayout({
  bindings: [
    {binding: 0, visibility: GPUShaderStage.COMPUTE, type: "storage-buffer"},
    {binding: 1, visibility: GPUShaderStage.COMPUTE, type: "storage-buffer"},
    {binding: 2, visibility: GPUShaderStage.COMPUTE, type: "storage-buffer"}
  ]
});

const bindGroup = device.createBindGroup({
  layout: bindGroupLayout,
  bindings: [
    {binding: 0, resource: {buffer: gpuBufferFirstMatrix}},
    {binding: 1, resource: {buffer: gpuBufferSecondMatrix}},
    {binding: 2, resource: {buffer: resultMatrixBuffer}}
  ]
});

const computeShaderCode = `#version 450
  layout(std430, set = 0, binding = 0) readonly buffer FirstMatrix {
  } firstMatrix;

  layout(std430, set = 0, binding = 1) readonly buffer SecondMatrix {
  } secondMatrix;

  layout(std430, set = 0, binding = 2) buffer ResultMatrix {
  } resultMatrix;`;

const computePipeline = device.createComputePipeline({
  layout: device.createPipelineLayout({
    bindGroupLayouts: [bindGroupLayout]
  }),
  computeStage: {
    module: device.createShaderModule({code: theCode}),
    entryPoint: "main"
  }
});

into

const bindGroup = device.createBindGroup({
  bindings: [
    {binding: 0, resource: {buffer: gpuBufferFirstMatrix}},
    {binding: 1, resource: {buffer: gpuBufferSecondMatrix}},
    {binding: 2, resource: {buffer: resultMatrixBuffer}}
  ]
});

const computeShaderCode = `#version 450
  layout(std430, set = 0, binding = 0) readonly buffer FirstMatrix {
  } firstMatrix;

  layout(std430, set = 0, binding = 1) readonly buffer SecondMatrix {
  } secondMatrix;

  layout(std430, set = 0, binding = 2) buffer ResultMatrix {
  } resultMatrix;`;

const computePipeline = device.createComputePipeline({
  computeStage: {
    module: device.createShaderModule({code: theCode}),
    entryPoint: "main"
  }
});

which is much easier to understand for people getting started with WebGPU, and almost 50% less code to type for experienced WebGPU developers hacking with the API.

How would this work

It makes the layout member of GPUPipelineDescriptorBase and GPUBindGroupDescriptor optional and if not present deduces them using the following algorithms.

For GPUBindGroupDescriptor it implicitly creates a GPUBindGroupLayout that one binding (with the same binding number) for each binding in the GPUBindGroupDescriptor. visibility is always all the stage and other member are set like so (if not described, they get their default value):

• If the resource is a GPUSampler, type is "sampler"
• If the resource is a GPUTextureView, if the texture has not exactly one of the SAMPLED and STORAGE usages, an error is produced. type is "sampled-texture" if the texture has the SAMPLED usage, "storage-texture" otherwise. textureDimension is set to the texture view dimension of the view, and textureComponentType set to the component type of the texture's format. If the texture has a sampleCount larger than 1, multisampled is set so true.
• If the resource is a GPUBufferBinding, if the buffer has not exactly one of the UNIFORM and STORAGE usages, an error is produced. type is "uniform-buffer" if the buffer has the UNIFORM usage, "storage-buffer" otherwise.

For GPUComputePipeline and GPURenderPipeline we would deduce an implicit GPUPipelineLayout that has implicit GPUBindGroupLayouts for each set used by the pipeline. visibility is set to all shader stages. Then for each binding of the shader modules of the pipeline a binding is inserted in the correct GPUBindGroupLayout with the matching binding like the following (members not mentioned get their default value):

• For sampler bindings in the shadermodule, type is set to "sampler".
• For uniform buffer bindings, type is set to "uniform-buffer".
• For storage buffer bindings, type is set to "storage-buffer".
• For texture bindings, if the texture (SPIRV-ism) has the Sampled bit set to 0, type is set to storage-texture, sampled-texture otherwise. textureViewDimension is set to match the texture binding declaration, as is multisampled and textureComponentType.

Note that for render pipeline this would also require checking no two bindings conflict.