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

mixin LightGridCommon
{
	code
	{
		cbuffer GridParams : register(b4)
		{
			// Offsets at which specific light types begin in gLights buffer
			// Assumed directional lights start at 0
			// x - offset to point lights, y - offset to spot lights, z - total number of lights
			uint3 gLightOffsets;
			uint gNumReflProbes;
			uint gNumCells;
			uint3 gGridSize;
			uint gMaxNumLightsPerCell;
			uint2 gGridPixelSize;
		}
					
		float calcViewZFromCellZ(uint cellZ)
		{
			// We don't want to subdivide depth uniformly because XY sizes will be much
			// smaller closer to the near plane, and larger towards far plane. We want 
			// our cells to be as close to cube shape as possible, so that width/height/depth
			// are all similar. Ideally we would use either width or height as calculated for
			// purposes of the projection matrix, for the depth. But since we'll be splitting
			// the depth range into multiple slices, in practice this ends up with many tiny
			// cells close to the near plane. Instead we use a square function, which is
			// somewhere between the two extremes:
			//  view = slice^2
			
			// We need it in range [near, far] so we normalize and scale
			//  view = slice^2 / maxSlices^2 * (far - near) + near
			
			// Note: Some of these calculations could be moved to CPU
			float viewZ = (pow(cellZ, 2) / pow(gGridSize.z, 2)) * (gNearFar.y - gNearFar.x) + gNearFar.x; 
			return -viewZ;
		}
		
		uint calcCellZFromViewZ(float viewZ)
		{
			// Inverse of calculation in calcViewZFromCellZ
			uint cellZ = min((uint)floor(sqrt(((-viewZ - gNearFar.x)*pow(gGridSize.z, 2))/(gNearFar.y - gNearFar.x))), gGridSize.z);
			
			return cellZ;
		}
		
		uint calcCellIdx(uint2 pixelPos, float deviceZ)
		{
			// OpenGL uses lower left for window space origin
			#ifdef OPENGL
				pixelPos.y = gViewportRectangle.w - pixelPos.y;
			#endif			
		
			// Note: Use bitshift to divide since gGridPixelSize will be a power of 2
			uint2 cellXY = pixelPos / gGridPixelSize;
			uint cellZ = calcCellZFromViewZ(convertFromDeviceZ(deviceZ));
			
			uint cellIdx = (cellZ * gGridSize.y + cellXY.y) * gGridSize.x + cellXY.x;
			return cellIdx;
		}
	};
};