75 lines
3.7 KiB
C++
75 lines
3.7 KiB
C++
// Copyright Epic Games, Inc. All Rights Reserved.
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#pragma once
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#include "CoreMinimal.h"
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#include "LMMath.h"
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namespace Lightmass
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{
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/** Generates valid X and Y axes of a coordinate system, given the Z axis. */
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void GenerateCoordinateSystem(const FVector4f& ZAxis, FVector4f& XAxis, FVector4f& YAxis);
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/** Generates a pseudo-random unit vector, uniformly distributed over all directions. */
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FVector4f GetUnitVector(FLMRandomStream& RandomStream);
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/** Generates a pseudo-random position inside the unit sphere, uniformly distributed over the volume of the sphere. */
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FVector4f GetUnitPosition(FLMRandomStream& RandomStream);
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/**
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* Generates a pseudo-random unit vector in the Z > 0 hemisphere whose PDF == 1 / (2 * PI) in solid angles,
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* Or sin(theta) / (2 * PI) in hemispherical coordinates, which is a uniform distribution over the area of the hemisphere.
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*/
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FVector4f GetUniformHemisphereVector(FLMRandomStream& RandomStream, float MaxTheta = (float)HALF_PI);
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/**
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* Generates a pseudo-random unit vector in the Z > 0 hemisphere whose PDF == cos(theta) / PI in solid angles,
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* Which is sin(theta)cos(theta) / PI in hemispherical coordinates.
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*/
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FVector4f GetCosineHemisphereVector(FLMRandomStream& RandomStream, float MaxTheta = (float)HALF_PI);
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/**
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* Generates a pseudo-random unit vector in the Z > 0 hemisphere,
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* Whose PDF == (SpecularPower + 1) / (2.0f * PI) * cos(Alpha) ^ SpecularPower in solid angles,
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* Where Alpha is the angle between the perfect specular direction and the outgoing direction.
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*/
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FVector4f GetModifiedPhongSpecularVector(FLMRandomStream& RandomStream, const FVector4f& TangentSpecularDirection, float SpecularPower);
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/**
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* Generates a pseudo-random position within a unit disk,
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* Whose PDF == 1 / PI, which is a uniform distribution over the area of the disk.
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*/
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FVector2f GetUniformUnitDiskPosition(FLMRandomStream& RandomStream);
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/**
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* Generates a pseudo-random direction within a cone,
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* Whose PDF == 1 / (2 * PI * (1 - CosMaxConeTheta)), which is a uniform distribution over the directions in the cone.
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*/
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FVector4f UniformSampleCone(FLMRandomStream& RandomStream, float CosMaxConeTheta, const FVector4f& XAxis, const FVector4f& YAxis, const FVector4f& ZAxis);
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FVector4f UniformSampleCone(float CosMaxConeTheta, const FVector4f& XAxis, const FVector4f& YAxis, const FVector4f& ZAxis, float Uniform1, float Uniform2);
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/** Calculates the PDF for a sample generated by UniformSampleCone */
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float UniformConePDF(float CosMaxConeTheta);
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FVector4f UniformSampleHemisphere(float Uniform1, float Uniform2);
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/** Generates unit length, stratified and uniformly distributed direction samples in a hemisphere. */
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void GenerateStratifiedUniformHemisphereSamples(int32 NumThetaSteps, int32 NumPhiSteps, FLMRandomStream& RandomStream, TArray<FVector4f>& Samples, TArray<FVector2f>& Uniforms);
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void GenerateStratifiedCosineHemisphereSamples(int32 NumThetaSteps, int32 NumPhiSteps, FLMRandomStream& RandomStream, TArray<FVector4f>& Samples);
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/**
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* Multiple importance sampling power heuristic of two functions with a power of two.
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* From Veach's PHD thesis titled "Robust Monte Carlo Methods for Light Transport Simulation", page 273.
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*/
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float PowerHeuristic(int32 NumF, float fPDF, int32 NumG, float gPDF);
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/** Calculates the step 1D cumulative distribution function for the given unnormalized probability distribution function. */
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void CalculateStep1dCDF(const TArray<float>& PDF, TArray<float>& CDF, float& UnnormalizedIntegral);
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/** Generates a Sample from the given step 1D probability distribution function. */
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void Sample1dCDF(const TArray<float>& PDFArray, const TArray<float>& CDFArray, float UnnormalizedIntegral, FLMRandomStream& RandomStream, float& PDF, float& Sample);
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}
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