WebGPU MVP bans arrays of resources (allows Texture2DArray)

[dneto0]

From F2F 2019-05-16.
Minutes doc

Decision: No arrays of resources in MVP. Texture2DArray is allowed (it’s not an array in the shader language.) Reconsider resource count limit is increased much larger than 32.

[dneto0]

At the moment the WHLSL spec permits certain arrayed texture resource.
See https://github.com/gpuweb/WHLSL/blob/master/Spec/source/index.rst

Copying from there:

Texture1D<T>
RWTexture1D<T>
Texture1DArray<T>
RWTexture1DArray<T>
Texture2D<T>
RWTexture2D<T>
Texture2DArray<T>
RWTexture2DArray<T>
Texture3D<T>
RWTexture3D<T>
TextureCube<T>
TextureDepth2D<float>
RWTextureDepth2D<float>
TextureDepth2DArray<float>
RWTextureDepth2DArray<float>
TextureDepthCube<float>

and a TODO for Texture2DMS<T>, TextureDepth2DMS<float>

[dneto0]

In particular, that leaves out CubeArray. For index clamping CubeArray has an odd corner case where in Vulkan/SPIR-V the layer count and face index is folded together into the last component of the coordinate of the OpImageTexelPointer call. So even if we have a max layer of N we have to make sure 6*N does not overflow the integer.
Fortunately we can ignore that case.