#include "$ENGINE$\PPBase.bslinc"

technique PPEyeAdaptHistogramReduce
{
	mixin PPBase;

	code
	{
		[internal]
		cbuffer Input
		{
			uint gThreadGroupCount;
		}		
	
		Texture2D gHistogramTex;
		Texture2D gEyeAdaptationTex;

		float4 fsmain(VStoFS input) : SV_Target0
		{
			int2 iUV = trunc(input.uv0);
			float4 outputValue = 0.0f;

			// Output texture only has two rows, store histogram on the first
			if(input.uv0.y < 1.0f)
			{
				// TODO - Potentially optimize using bilinear filtering
				for(uint i = 0; i < gThreadGroupCount; i++)
					outputValue += gHistogramTex.Load(int3(iUV.x, i, 0));

				return outputValue / gThreadGroupCount;
			}
			else
			{
				// Store eye adaptation from last frame in the second row of the texture
				return gEyeAdaptationTex.Load(int3(0, 0, 0)).x;
			}
		}	
	};
};