mixin ColorSpace
{
	code
	{
		/**
		 * Converts a color in RGB space into YCoCg color space. Note that Co and Cg
		 * components are in [-0.5, 0.5] range and therefore cannot be stored as-is
		 * in a normal color texture.
		 */
		float3 RGBToYCoCg(float3 input)
		{
			float Y = dot(input, float3(0.25f, 0.5f, 0.25f));
			float Co = input.r * 0.5f + input.b * -0.5f;
			float Cg = dot(input, float3(-0.25f, 0.5f, -0.25f));
			
			return float3(Y, Co, Cg);
		}
		
		/**
		 * Converts a color in YCoCg color space into RGB color space.
		 */
		float3 YCoCg(float3 input)
		{
			float R = input.r + input.g - input.b;
			float G = input.r + input.b;
			float B = input.r - input.g - input.b;
			
			return float3(R, G, B);
		}
		
		/** Calculates luminance from a color in RGB color space. */
		float LuminanceRGB(float3 input)
		{
			return 0.299f * input.r + 0.587f * input.g + 0.114f * input.b;
		}
		
		////////////////////// HDR SCALING HELPER FUNCTIONS ///////////////////
		// HDR scaling methods use luminance based scaling, instead of a tonemap operator, as
		// described here:
		// http://graphicrants.blogspot.hr/2013/12/tone-mapping.html
		float HDRScaleWeight(float luma, float exposureScale)
		{
			return rcp(1 + luma * exposureScale);
		}
		
		float HDRScaleWeightInv(float luma, float exposureScale)
		{
			return rcp(1 - luma * exposureScale);
		}		
		
		float3 HDRScaleRGB(float3 v, float exposureScale)
		{
			float luma = LuminanceRGB(v);
			
			return v * HDRScaleWeight(luma, exposureScale);
		}
		
		float3 HDRScaleY(float3 v, float exposureScale)
		{
			float luma = v.r;
			
			return v * HDRScaleWeight(luma, exposureScale);
		}
		
		float3 HDRScaleG(float3 v, float exposureScale)
		{
			float luma = v.g;
			
			return v * HDRScaleWeight(luma, exposureScale);
		}

		float3 HDRScaleRGBInv(float3 v, float exposureScale)
		{
			float luma = LuminanceRGB(v);
			
			return v * HDRScaleWeightInv(luma, exposureScale);
		}
		
		float3 HDRScaleYInv(float3 v, float exposureScale)
		{
			float luma = v.r;
			
			return v * HDRScaleWeightInv(luma, exposureScale);
		}
		
		float3 HDRScaleGInv(float3 v, float exposureScale)
		{
			float luma = v.g;
			
			return v * HDRScaleWeightInv(luma, exposureScale);
		}				
	};
};