gray scale shader

hello-world.hlsl

Texture2D tex_scene : register(t0, space2);
SamplerState sam_scene : register(s0, space2);

struct Input {
  float4 tex_color : COLOR0;
  float2 tex_coord : TEXCOORD0;
};

struct Output {
  float4 frag_color : SV_Target;
};

Output main(Input input) {
  Output output;
  float4 color = tex_scene.Sample(sam_scene, input.tex_coord) * input.tex_color;
  // https://en.wikipedia.org/wiki/Grayscale
  float4 luma = dot(color.rgb, float3(0.2126, 0.7152, 0.0722));
  output.frag_color = float4(luma.r, luma.g, luma.b, color.a);
  return output;
}