Version: Unity 6 (6000.0)
Language : English
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Writing compute shaders for multiple platforms

Cross-platform best practices

DirectX 11 (DX11) supports many actions that are not supported on other platforms (such as Metal or OpenGL ES). Therefore, you should always ensure your shaderA program that runs on the GPU. More info
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has well-defined behavior on platforms that offer less support, rather than only on DX11. Here are few things to consider:

  • 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:
GraphicsFormat RenderTextureFormat HLSL type GLSL image format qualifier
R32G32B32A32_SFloat ARGBFloat float4 rgba32f
R16G16B16A16_SFloat ARGBHalf min16float4/half4 rgba16f
R32G32_SFloat RGFloat float2 rg32f
R16G16_SFloat RGHalf min16float2/half2 rg16f
B10G11R11_UFloatPack32 RGB111110Float min10float3 r11f_g11g_b10f
R32_SFloat RFloat float r32f
R16_SFloat RHalf min16float/half r16f
R16G16B16A16_UNorm ARGB64 unorm min16float4/half4 rgba16
A2B10G10R10_UNormPack32 ARGB2101010 unorm min10float4 rgb10_a2
R8G8B8A8_UNorm ARGB32 unorm float4 rgba8
R16G16_UNorm RG32 unorm min16float2/half2 rg16
R8G8_UNorm RG16 unorm float2 rg8
R16_UNorm R16 unorm min16float/half r16
R8_UNorm R8 unorm float r8
R16G16B16A16_SNorm unsupported snorm min16float4/half4 rgba16_snorm
R8G8B8A8_SNorm unsupported snorm float4 rgba8_snorm
R16G16_SNorm unsupported snorm min16float2/half2 rg16_snorm
R8G8_SNorm unsupported snorm float2 rg8_snorm
R16_SNorm unsupported snorm min16float/half r16_snorm
R8_SNorm unsupported snorm float r8_snorm
R32G32B32A32_SInt ARGBInt int4 rgba32i
R16G16B16A16_SInt unsupported min16int4 rgba16i
R8G8B8A8_SInt unsupported min12int4 rgba8i
R32G32_SInt RGInt int2 rg32i
R16G16_SInt unsupported min16int2 rg16i
R8G8_SInt unsupported min12int2 rg8i
R32_SInt RInt int r32i
R16_SInt unsupported min16int r16i
R8_SInt unsupported min12int r8i
R32G32B32A32_UInt unsupported uint4 rgba32i
R16G16B16A16_UInt RGBAUShort min16uint4 rgba16ui
R8G8B8A8_UInt unsupported unsupported rgba8ui
R32G32_UInt unsupported uint2 rg32ui
R16G16_UInt unsupported min16uint2 rg16ui
R8G8_UInt unsupported unsupported rg8ui
R32_UInt unsupported uint r32ui
R16_UInt unsupported min16uint r16ui
R8_UInt unsupported unsupported r8ui
A2B10G10R10_UIntPack32 unsupported unsupported rgb10_a2ui
Run a compute shader
Optimize shaders