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

Technique : base("LightGridCommon") =
{
	Pass =
	{
		Common = 
		{
			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)
			{
				// 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;
			}
		};
	};
};