UnrealEngineUWP/Engine/Shaders/DeferredLightVertexShaders.usf

// Copyright 1998-2015 Epic Games, Inc. All Rights Reserved.

/*=============================================================================
	DeferredLightVertexShaders.usf: 
=============================================================================*/

#include "Common.usf"

float4 StencilingGeometryPosAndScale;
float4 StencilingConeParameters;	// .x NumSides (0 if not cone), .y NumSlices, .z ConeAngle, .w ConeSphereRadius
float4x4 StencilingConeTransform;
float3 StencilingPreViewTranslation;

/** Vertex shader for rendering a directional light using a full screen quad. */
void DirectionalVertexMain(
	in float2 InPosition : ATTRIBUTE0,
	in float2 InUV       : ATTRIBUTE1,
	out float2 OutTexCoord : TEXCOORD0,
	out float3 OutScreenVector : TEXCOORD1,
	out float4 OutPosition : SV_POSITION
	)
{	
	DrawRectangle(float4(InPosition.xy, 0, 1), InUV, OutPosition, OutTexCoord);
	OutScreenVector = mul(float4(OutPosition.xy, 1, 0), View.ScreenToTranslatedWorld).xyz;
}

/** Vertex shader for rendering a point or spot light using approximate bounding geometry. */
void RadialVertexMain(
	in uint InVertexId : SV_VertexID,
	in float3 InPosition : ATTRIBUTE0,
	out float4 OutScreenPosition : TEXCOORD0,
	out float4 OutPosition : SV_POSITION
	)
{
	float3 WorldPosition;
	uint NumSides = StencilingConeParameters.x;
	if (NumSides != 0)
	{
		float SphereRadius = StencilingConeParameters.w;
		float ConeAngle = StencilingConeParameters.z;

		// Cone vertex shader
		const float InvCosRadiansPerSide = 1.0f / cos(PI / (float)NumSides);
		// Use Cos(Theta) = Adjacent / Hypotenuse to solve for the distance of the end of the cone along the cone's Z axis
		const float ZRadius = SphereRadius * cos(ConeAngle);
		const float TanConeAngle = tan(ConeAngle);

		uint NumSlices = StencilingConeParameters.y;
		uint CapIndexStart = NumSides * NumSlices;
		// Generate vertices for the cone shape
		if (InVertexId < CapIndexStart)
		{
			uint SliceIndex = InVertexId / NumSides;
			uint SideIndex = InVertexId % NumSides;

			const float CurrentAngle = SideIndex * 2 * PI / (float)NumSides;
			const float DistanceDownConeDirection = ZRadius * SliceIndex / (float)(NumSlices - 1);
			// Use Tan(Theta) = Opposite / Adjacent to solve for the radius of this slice
			// Boost the effective radius so that the edges of the circle lie on the cone, instead of the vertices
			const float SliceRadius = DistanceDownConeDirection * TanConeAngle * InvCosRadiansPerSide;
			// Create a position in the local space of the cone, forming a circle in the XY plane, and offsetting along the Z axis
			const float3 LocalPosition = float3(ZRadius * SliceIndex / (float)(NumSlices - 1), SliceRadius * sin(CurrentAngle), SliceRadius * cos(CurrentAngle));
			// Transform to world space and apply pre-view translation, since these vertices will be used with a shader that has pre-view translation removed
			WorldPosition = mul(float4(LocalPosition, 1), StencilingConeTransform).xyz + StencilingPreViewTranslation;
		}
		else
		{
			// Generate vertices for the spherical cap
			const float CapRadius = ZRadius * tan(ConeAngle);

			uint VertexId = InVertexId - CapIndexStart;
			uint SliceIndex = VertexId / NumSides;
			uint SideIndex = VertexId % NumSides;

			const float UnadjustedSliceRadius = CapRadius * SliceIndex / (float)(NumSlices - 1);
			// Boost the effective radius so that the edges of the circle lie on the cone, instead of the vertices
			const float SliceRadius = UnadjustedSliceRadius * InvCosRadiansPerSide;
			// Solve for the Z axis distance that this slice should be at using the Pythagorean theorem
			const float ZDistance = sqrt(SphereRadius * SphereRadius - UnadjustedSliceRadius * UnadjustedSliceRadius);

			const float CurrentAngle = SideIndex * 2 * PI / (float)NumSides;
			const float3 LocalPosition = float3(ZDistance, SliceRadius * sin(CurrentAngle), SliceRadius * cos(CurrentAngle));
			WorldPosition = mul(float4(LocalPosition, 1), StencilingConeTransform).xyz + StencilingPreViewTranslation;
		}
	}
	else
	{
		// Sphere
		WorldPosition = InPosition * StencilingGeometryPosAndScale.w + StencilingGeometryPosAndScale.xyz;
	}

	OutScreenPosition = OutPosition = mul(float4(WorldPosition, 1), View.TranslatedWorldToClip);
}