ARB_texture_swizzle "emulation" for D3D

swizzle.hlsl

uniform float4 weightsR; // default 1,0,0,0
uniform float4 weightsG; // default 0,1,0,0
uniform float4 weightsB; // default 0,0,1,0
uniform float4 weightsA; // default 0,0,0,1

float4 swizzledTex2D (sampler2D smp, float2 uv)
{
  float4 smp = tex2D (mysampler, myuv);
  float4 res;
  res.r = dot(smp,weightsR);
  res.g = dot(smp,weightsG);
  res.b = dot(smp,weightsB);
  res.a = dot(smp,weightsA);
  return res;
}

// for example to splat just R channel of a texture into all four channels, set up
// weightsR..A to all be (1,0,0,0)