The chromium_experimental_framebuffer_fetch extension adds support for framebuffer inputs to fragment stages in WGSL. Framebuffer input, or framebuffer fetch, lets a fragment shader read the value of framebuffer attachments for the current fragment. It synchronizes the read with all previous writes to the same fragment (in API order).
Framebuffer Fetch support in Tint is experimental and might change as we gain implementation experience. It will also be updated to follow an upstream specification if one is made at some point. Specification work in the WebGPU group hasn't started.
This adds a new builtin attribute @color which takes a u32 argument and is only allowed on @fragment entry point scalar / vector inputs. Two input variables cannot have the same @color attribute.
@fragment fn main(@color(0) vec4f previousColor) -> @location(0) vec4f {
let color = computeThisFragmentColor();
return myBlend(previousColor, color);
}
@color inputs?