mirror.frag

#version 450

layout (location = 0) in vec4 inPos;

layout (location = 0) out vec4 outColor;

layout (set = 1, binding = 1) uniform sampler2D diffuseMap;

void main() {
  vec4 tmp = vec4(1.0 / inPos.w);
  vec4 projCoord = inPos * tmp;

  // Scale and bias
  projCoord += vec4(1.0 * -1);
  projCoord *= vec4(0.5 * -1);

  // Slow single pass blur
  // For demonstration purposes only
  const float blurSize = 1.0 / 512.0;

  outColor = vec4(vec3(0.0), 1.0);

  if (gl_FrontFacing)
  {
    // Only render mirrored scene on front facing (upper) side of mirror surface
    vec4 reflection = vec4(0.0);
    for (int x = -3; x <= 3; x++)
    {
      for (int y = -3; y <= 3; y++)
      {
        // Flip texture coordinates for reflection
        vec2 flippedTexCoord = vec2(1.0 - (projCoord.s + x * blurSize), projCoord.t + y * blurSize);
        reflection += texture(diffuseMap, flippedTexCoord) / 49.0;
      }
    }
    outColor += reflection;
  }

}