pex-renderer/shaders/chunks/oct-map.glsl.js

Physically Based Renderer for Pex

module.exports = /* glsl */ `
vec2 envMapOctahedral(vec3 dir) {
  dir /= dot(vec3(1.0), abs(dir));
  // Add epsylon to avoid bottom face flickering when sampling irradiance
  dir += 0.00001;
  if (dir.y < 0.0) {
    dir.xy = vec2(1.0 - abs(dir.zx)) * sign(dir.xz);
  }
  else {
    dir.xy = dir.xz;
  }
  dir.xy = dir.xy * 0.5;
  dir.xy += 0.5; // move to center
  // dir.xy = (dir.xy * 64.0 + 1.0) / 66.0;
  return dir.xy;
}

vec2 envMapOctahedral(vec3 dir, float textureSize) {
  dir /= dot(vec3(1.0), abs(dir));
  if (dir.y < 0.0) {
    dir.xy = vec2(1.0 - abs(dir.zx)) * sign(dir.xz);
  }
  else {
    dir.xy = dir.xz;
  }
  dir.xy = dir.xy * 0.5;
  dir.xy += 0.5; // move to center

  // center on texels
  dir.xy += 0.5 / textureSize;
  dir.xy /= textureSize / (textureSize - 1.0);

  return dir.xy;
}

vec2 envMapOctahedral(vec3 dir, float mipmapLevel, float roughnessLevel) {
  float width = 2048.0;
  float maxLevel = 11.0; // this should come from log of size
  float levelSizeInPixels = pow(2.0, 1.0 + mipmapLevel + roughnessLevel);
  float levelSize = max(64.0, width / levelSizeInPixels);
  float roughnessLevelWidth = width / pow(2.0, 1.0 + roughnessLevel);
  float vOffset = (width - pow(2.0, maxLevel - roughnessLevel));
  float hOffset = 2.0 * roughnessLevelWidth - pow(2.0, log2(2.0 * roughnessLevelWidth) - mipmapLevel);
  vec2 uv = envMapOctahedral(dir, levelSize);
  uv *= levelSize;

  return (uv + vec2(hOffset, vOffset)) / width;
}
`