BeRo1985

// GLSL Octahedral Texture Mapping with Edge Mirroring and Bilinear Interpolation (by Benjamin 'BeRo' Rosseaux)

ivec2 wrapOctahedralTexelCoordinates(const in ivec2 texel, const in ivec2 texSize) {
  ivec2 wrapped = ((texel % texSize) + texSize) % texSize;
  return ((((abs(texel.x / texSize.x) + int(texel.x < 0)) ^ (abs(texel.y / texSize.y) + int(texel.y < 0))) & 1) != 0) ? (texSize - (wrapped + ivec2(1))) : wrapped;
}

vec4 textureOctahedralMap(const in sampler2D tex, vec3 direction) {
  direction = normalize(direction); // just for to make sure that it is normalized 
  vec2 uv = direction.xy / (abs(direction.x) + abs(direction.y) + abs(direction.z));