Dual Source Blending

The dual-source-blending feature adds additional blend factors and the WGSL @index attribute to allow a fragment shader to blend two color outputs into a single output buffer.

This feature adds the following wgpu::BlendFactors:

  • Src1
  • OneMinusSrc1
  • Src1Alpha
  • OneMinusSrc1Alpha

This feature introduces the @index WGSL attribute. This attribute is added to a fragment output at @location(0) to denote the blending source index. You must use enable chromium_internal_dual_source_blending in a shader to use the @index attribute.

Example Fragment Shader:

    enable chromium_internal_dual_source_blending;

    struct FragOut {
        @location(0) @index(0) color : vec4<f32>,
        @location(0) @index(1) blend : vec4<f32>,

    @fragment fn main() -> FragOut {
        var output : FragOut;
        output.color = {1.0, 1.0, 1.0, 1.0};
        output.blend = {0.5, 0.5, 0.5, 0.5};
        return output;


- Dual source blending must occur on color attachment 0.
- Dual source blending makes it invalid to render to multiple render targets.