Dual-source blending in DirectX 11

It's not described in the documentation, but dual-source blending in DirectX 11 D3D11_BLEND_SRC1_COLOR is achieved using SV_TARGET1. You would have a BlendState like this (all in fx format):

BlendState CompositeBlend { BlendEnable[0] =TRUE; SrcBlend =ONE; DestBlend =SRC1_COLOR; BlendOp =ADD; };

And an output structure that looks like it's writing to two rendertargets. But you only have one rendertarget!

struct TwoColourOutput { float4 add :SV_TARGET0; float4 multiply :SV_TARGET1; };

And then the pixel shader does:

TwoColourOutput PSMain(v2f IN) : SV_TARGET { TwoColourOutput result =... return result; }

The result - the value in the rendertarget is multiplied by result.multiply, and then result.add is added to it. Viola!