uniform samplerCube probeDepth;
uniform int outputSize;
uniform float lodFactor;
uniform float storedTexelSize;
uniform float lodMax;
uniform float nearClip;
uniform float farClip;
uniform float visibilityRange;
uniform float visibilityBlur;

out vec4 FragColor;

vec3 octahedral_to_cubemap_proj(vec2 co)
{
  co = co * 2.0 - 1.0;

  vec2 abs_co = abs(co);
  vec3 v = vec3(co, 1.0 - (abs_co.x + abs_co.y));

  if (abs_co.x + abs_co.y > 1.0) {
    v.xy = (abs(co.yx) - 1.0) * -sign(co.xy);
  }

  return v;
}

float linear_depth(float z)
{
  return (nearClip * farClip) / (z * (nearClip - farClip) + farClip);
}

float get_world_distance(float depth, vec3 cos)
{
  float is_background = step(1.0, depth);
  depth = linear_depth(depth);
  depth += 1e1 * is_background;
  cos = normalize(abs(cos));
  float cos_vec = max(cos.x, max(cos.y, cos.z));
  return depth / cos_vec;
}

void main()
{
  ivec2 texel = ivec2(gl_FragCoord.xy) % ivec2(outputSize);

  vec3 cos;

  cos.xy = (vec2(texel) + 0.5) * storedTexelSize;

  /* add a 2 pixel border to ensure filtering is correct */
  cos.xy = (cos.xy - storedTexelSize) / (1.0 - 2.0 * storedTexelSize);

  float pattern = 1.0;

  /* edge mirroring : only mirror if directly adjacent
   * (not diagonally adjacent) */
  vec2 m = abs(cos.xy - 0.5) + 0.5;
  vec2 f = floor(m);
  if (f.x - f.y != 0.0) {
    cos.xy = 1.0 - cos.xy;
  }

  /* clamp to [0-1] */
  cos.xy = fract(cos.xy);

  /* get cubemap vector */
  cos = normalize(octahedral_to_cubemap_proj(cos.xy));

  vec3 T, B;
  make_orthonormal_basis(cos, T, B); /* Generate tangent space */

  vec2 accum = vec2(0.0);

  for (float i = 0; i < sampleCount; i++) {
    vec3 sample = sample_cone(i, M_PI_2 * visibilityBlur, cos, T, B);
    float depth = texture(probeDepth, sample).r;
    depth = get_world_distance(depth, sample);
    accum += vec2(depth, depth * depth);
  }

  accum *= invSampleCount;
  accum = abs(accum);

  /* Encode to normalized RGBA 8 */
  FragColor = visibility_encode(accum, visibilityRange);
}