BansheeEngine/Data/Raw/Engine/Includes/ReflectionCubemapCommon.bslinc

Technique : base("ReflectionCubemapCommon") =
{
	Pass =
	{
		Common = 
		{
			float3 getDirFromCubeFace(uint cubeFace, float2 uv)
			{
				float3 dir;
				if(cubeFace == 0)
					dir = float3(1.0f, -uv.y, -uv.x);
				else if(cubeFace == 1)
					dir = float3(-1.0f, -uv.y, uv.x);
				else if(cubeFace == 2)
					dir = float3(uv.x, 1.0f, uv.y);
				else if(cubeFace == 3)
					dir = float3(uv.x, -1.0f, -uv.y);
				else if(cubeFace == 4)
					dir = float3(uv.x, -uv.y, 1.0f);
				else
					dir = float3(-uv.x, -uv.y, -1.0f);
					
				return dir;
			}
			
			/**
			 * Calculates a mip level to sample from based on roughness value.
			 *
			 * @param 	roughness	Roughness in range [0, 1]. Higher values yield more roughness.
			 * @param	numMips		Total number of mip-map levels in the texture we'll be sampling from.
			 * @return				Index of the mipmap level to sample.
			 */					
			float mapRoughnessToMipLevel(float roughness, int numMips)
			{
				// We use the following equation:
				//    mipLevel = log10(1 - roughness) / log10(dropPercent)
				//
				// Where dropPercent represent by what % to drop the roughness with each mip level.
				// We convert to log2 and a assume a drop percent value of 0.7. This gives us:
				//    mipLevel = -2.8 * log2(1 - roughness);
				
				// Note: Another value that could be used is drop 0.6, which yields a multiply by -1.35692. 
				// This more accurately covers the mip range, but early mip levels end up being too smooth,
				// and benefits from our cubemap importance sampling strategy seem to be lost as most samples
				// fall within one pixel, resulting in same effect as just trivially downsampling. With 0.7 drop
				// the roughness increases too early and higher mip levels don't cover the full [0, 1] range. Which
				// is better depends on what looks better.
				
				return max(0, -2.8f * log2(1.0f - roughness));
			}
			
			/**
			 * Calculates a roughness value from the provided mip level.
			 *
			 * @param 	mipLevel	Mip level to determine roughness for.
			 * @param	numMips		Total number of mip-map levels in the texture we'll be sampling from.
			 * @return				Roughness value for the specific mip level.
			 */				
			float mapMipLevelToRoughness(int mipLevel, int numMips)
			{
				// mapRoughnessToMipLevel() solved for roughness
				return 1 - exp2((float)mipLevel / -2.8f);
			}	
		};
	};
};