diff options
| -rw-r--r-- | docs/proposals/005-write-only-textures.md | 61 |
1 files changed, 61 insertions, 0 deletions
diff --git a/docs/proposals/005-write-only-textures.md b/docs/proposals/005-write-only-textures.md new file mode 100644 index 000000000..a68ed8c40 --- /dev/null +++ b/docs/proposals/005-write-only-textures.md @@ -0,0 +1,61 @@ +SP #005: Write-Only Textures +================= + +Add Write-Only texture types to Slang's core module. + + +Status +------ + +Status: Design Review. + +Implemtation: N/A + +Author: Yong He + +Reviewer: + +Background +---------- + +Slang inherits HLSL's RWTexture types to represent UAV/storage texture resources, this works well for HLSL, GLSL, CUDA and SPIRV targets. +However Metal has the notion of write only textures, and WebGPU has limited support of read-write textures. In WebGPU, a read-write texture can only have +uncompressed single-channel 32bit texel format, which means a `RWTexture2D` cannot be used to write to a `rgba8unorm` texture. + +To provide better mapping to write-only textures on Metal and WebGPU, we propose to add write-only textures to Slang to allow writing portable code +without relying on backend workarounds. + +Proposed Approach +----------------- + +Slang's core module already defines all texture types as a single generic `_Texture<T, ..., access, ...>` type, where `access` is a value parameter +representing the allowed access of the texture. The valid values of access are: + +``` +kCoreModule_ResourceAccessReadOnly +kCoreModule_ResourceAccessReadWrite +kCoreModule_ResourceAccessRasterizerOrdered +kCoreModule_ResourceAccessFeedback +``` + +We propose to add another case: + +``` +kCoreModule_ResourceAccessWriteOnly +``` + +to represent write-only textures. + + +Also add the typealiases prefixed with "W" for all write only textures: +``` +WTexture1D, WTexture2D, ... +``` + +These types will be reported in the reflection API with `access=SLANG_RESOURCE_ACCESS_WRITE`. + +Write-only textures support `GetDimension` and `Store(coord, value)` methods. `Load` or `subscript` is not defined for write-only texture types, +so the user cannot write code that reads from a write-only texture. + +Write only textures are supported on all targets. For traditional HLSL, GLSL, SPIRV and CUDA targets, they are translated +exactly the same as `RW` textures. For Metal, they map to `access::write`, and for WGSL, they map to `texture_storage_X<format, write>`. |