background.hlsl

float2 background(float2 uv, float2 resolution, float2 texResolution) {
  float tAspect = texResolution.x / texResolution.y;
  float pAspect = resolution.x / resolution.y;
  float pwidth = resolution.x;
  float pheight = resolution.y;

  float width = 0.0;
  float height = 0.0;
  if (tAspect > pAspect) {
    height = pheight;
    width = height * tAspect;
  }
  else {
    width = pwidth;
    height = width / tAspect;
  }
  float x = (pwidth - width) / 2.0;
  float y = (pheight - height) / 2.0;
  float2 nUv = uv;
  nUv -= float2(x, y) / resolution;
  nUv /= float2(width, height) / resolution;
  return nUv;
}