29 lines
1.2 KiB
Markdown
29 lines
1.2 KiB
Markdown
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# Chromium Experimental Push Constant
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The `chromium_experimental_push_constant` extension adds support for push constant global variables to WGSL.
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Push constants are small amounts of data that are passed to the shader and are expected to be more lightweight to set / modify than uniform buffer bindings.
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The concept of push constant comes from Vulkan but D3D12 has similar "root constants".
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Metal doesn't have the same concept but push constants can be efficiently implemented with the `setBytes` family of command encoder methods.
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## Status
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Push constant support in Tint is highly experimental and only meant to be used in internal transforms at this stage.
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Specification work in the WebGPU group hasn't started.
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## Pseudo-specification
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This extension adds a new `push_constant` storage class that's only allowed on global variable declarations.
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Push constant variables must only contain 32bit data types (or aggregates of such types).
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Push constant variable declarations must not have an initializer.
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It is an error for a entry point to statically use more than one `push_constant` variable.
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## Example usage
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```
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var<push_constant> draw_id : u32;
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@fragment fn main() -> u32 {
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return draw_id;
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}
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```
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