Writing compute shaders for multiple platforms

Cross-platform best practices

• Out-of-bounds memory accesses are bad. DX11 might consistently return zero when reading, and read some writes without issues, but platforms that offer less support might crash the GPU when doing this. Watch out for DX11-specific hacks, buffer sizes not matching with multiple of your thread group size, trying to read neighboring data elements from the beginning or end of the buffer, and similar incompatibilities.
• Initialize your resources. The contents of new buffers and Textures are undefined. Some platforms might provide all zeroes, but on others, there could be anything including NaNs.
• Bind all the resources your compute shader declares. Even if you know for sure that the shader does not use resources in its current state because of branching, you must still ensure a resource is bound to it.

Platform-specific differences

• Metal (for iOS and tvOS platforms) does not support atomic operations on Textures. Metal also does not support

  GetDimensions

  queries on buffers. Pass the buffer size info as constant to the shader if needed.
• OpenGL ES 3.1 (for (Android, iOS, tvOS platforms) only guarantees support for 4 compute buffers at a time. Actual implementations typically support more, but in general if developing for OpenGL ES, you should consider grouping related data in structs rather than having each data item in its own buffer.
• OpenGL (ES) and Vulkan require an image format qualifier for

  RWTextures<T>

  that are not write-only.
  Unity derives this qualifier from the type T in the angle-brackets. The format qualifier needs to match the GraphicsFormat/RenderTextureFormat of the RenderTexture that is bound to the RWTexture. The following table maps Unity RenderTexture GraphicsFormats and RenderTextureFormats to their corresponding HLSL type and image format qualifier: