cocos-creator-template/assets/chunks/common/texture/cubemap.chunk

// for specular-gloss workflow which support by legacy compatible lighting
float RoughnessToPerceptualRoughness(float roughness)
{
  return sqrt(roughness);
}

// for legacy only
#pragma extension([GL_OES_standard_derivatives, __VERSION__ < 110])
  vec3 EnvReflectionWithMipFiltering(vec3 R, float roughness, float mipCount, float denoiseIntensity) {
    #if CC_USE_IBL
      // simulate GGX convolution
      #if !CC_SURFACES_USE_LEGACY_COMPATIBLE_LIGHTING && !CC_IBL_CONVOLUTED
        roughness = RoughnessToPerceptualRoughness(roughness);
      #endif

      //#todo: add GL400 calcmip
    	float mip = roughness * (mipCount - 1.0);
    	float delta = (dot(dFdx(R), dFdy(R))) * 1000.0;
    	float mipBias = mix(0.0, 5.0, clamp(delta, 0.0, 1.0));

      vec3 rotationDir = RotationVecFromAxisY(R.xyz, cc_surfaceTransform.z, cc_surfaceTransform.w);
    	vec4 biased = fragTextureLod(cc_environment, rotationDir, mip + mipBias);
     	vec4 filtered = texture(cc_environment, rotationDir);

      #if CC_USE_IBL == IBL_RGBE
      	biased.rgb = unpackRGBE(biased);
      	filtered.rgb = unpackRGBE(filtered);
      #else
      	biased.rgb = SRGBToLinear(biased.rgb);
      	filtered.rgb = SRGBToLinear(filtered.rgb);
      #endif
      	
      return mix(biased.rgb, filtered.rgb, denoiseIntensity);
    #else
      return vec3(0.0, 0.0, 0.0);
    #endif
  }

  // for skybox IBL
  vec3 EnvReflection(samplerCube tex, vec3 R, float roughness, float mipCount) {
    // simulate GGX convolution
    #if !CC_SURFACES_USE_LEGACY_COMPATIBLE_LIGHTING && !CC_IBL_CONVOLUTED
      roughness = RoughnessToPerceptualRoughness(roughness);
    #endif

    vec3 rotationDir = RotationVecFromAxisY(R.xyz, cc_surfaceTransform.z, cc_surfaceTransform.w);
    vec4 envmap = fragTextureLod(tex, rotationDir, roughness * (mipCount - 1.0));
    #if CC_USE_IBL == IBL_RGBE
      return unpackRGBE(envmap);
    #else
      return SRGBToLinear(envmap.rgb);
    #endif

  }

  // for reflection probe
  vec3 EnvReflectionOfReflectionProbe(samplerCube tex, vec3 R, float roughness, float mipCount, bool isRGBE) {
    // simulate GGX convolution
    #if !CC_SURFACES_USE_LEGACY_COMPATIBLE_LIGHTING && !CC_IBL_CONVOLUTED
      roughness = RoughnessToPerceptualRoughness(roughness);
    #endif

    vec4 envmap = fragTextureLod(tex, R, roughness * (mipCount - 1.0));
    return isRGBE ? unpackRGBE(envmap) : SRGBToLinear(envmap.rgb);
  }