| # Chromium Experimental Push Constant |
| |
| The `chromium_experimental_push_constant` extension adds support for push constant global variables to WGSL. |
| 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. |
| The concept of push constant comes from Vulkan but D3D12 has similar "root constants". |
| Metal doesn't have the same concept but push constants can be efficiently implemented with the `setBytes` family of command encoder methods. |
| |
| ## Status |
| |
| Push constant support in Tint is highly experimental and only meant to be used in internal transforms at this stage. |
| Specification work in the WebGPU group hasn't started. |
| |
| ## Pseudo-specification |
| |
| This extension adds a new `push_constant` address space that's only allowed on global variable declarations. |
| Push constant variables must only contain 32bit data types (or aggregates of such types). |
| Push constant variable declarations must not have an initializer. |
| It is an error for a entry point to statically use more than one `push_constant` variable. |
| |
| ## Example usage |
| |
| ``` |
| var<push_constant> draw_id : u32; |
| |
| @fragment fn main() -> @location(0) u32 { |
| return draw_id; |
| } |
| ``` |
