ultilizing-the-uv-in-pixel-shaders.md

The UV is handy!

• The UV is not only used for textures, you can also make awesome effect out of it, this is how.
• Let's say we want to make a white circle that fades, the center of the UV is (0.5, 0.5), so we calculate the color based on the distance of the current UV to the center.

  float4 main(float2 uv : TEXCOORD) : SV_TARGET
  {
      float dist = distance(uv, float2(0.5f, 0.5f)) * 2.f;
      return 1.f - dist;
  }

• This is the result:
• 
• Or we could have an interesting effect using some simple math:

  #define M_PI 3.141592654f
  
  float4 main(float2 uv : TEXCOORD) : SV_TARGET
  {
      float dist = distance(uv, float2(0.5f, 0.5f)) * 2.f;
      float alpha = cos(dist * M_PI * 2.f * 5.f) * 0.5f + 0.5f;
      
      alpha *= 1.f - dist;
      return float4(color.rgb, alpha);
  }

• The result:
• 

Implement an animation

• By passing a time variable to the constant buffer, we could have animation:

  cbuffer cbPerFrame : register(c0)
  {
      float4 colorAndTime : register(c0); // {R, G, B, time}
  };
  
  #define M_PI 3.141592654f
  
  float4 main(float2 uv : TEXCOORD) : SV_TARGET
  {
      float3 color = colorAndTime.rgb;
      float time = colorAndTime[3]; // or colorAndTime.a
      
      float dist = distance(uv, float2(0.5f, 0.5f)) * 2.f;
      float alpha = cos((dist - time * 0.1f) * M_PI * 2.f * 5.f) * 0.5f + 0.5f;
      alpha *= 1.f - dist;
      return float4(color, alpha);
  }

• And in C++:

      static float time = 0.f; time += 0.01f;
      float psConstant[] = { 0.f, 1.f, 0.f, time };
      d3ddev->SetPixelShaderConstantF(0, psConstant, 1);

• The result:
•