UnrealEngine/Engine/Plugins/Runtime/MobileFSR/Shaders/Private/PostProcessMobileFFX_Common.ush

// Copyright Epic Games, Inc. All Rights Reserved.
//------------------------------------------------------------------------------
// Copyright (c) 2021 Advanced Micro Devices, Inc. All rights reserved.
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files(the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions :
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//------------------------------------------------------------------------------

// !!!
// FidelityFX Super Resolution - Common
// This header should be included after ffx_a.ush
// !!!

// =====================================================================================
// 
// EOTF Conversions
// 
// =====================================================================================
// FSR output device definitions : matching EFSR_OutputDevice enum in PostProcessFSR.cpp
#define FSR_SRGB   0
#define FSR_LINEAR 1
#define FSR_ST2084 2
#define FSR_scRGB  3

#define MAX_ODT_NITS_ENUM 0
#define CONVERT_TO_OUTPUT_DEVICE 0

#include "/Engine/Private/ACES/ACESCommon.ush"
#include "/Engine/Private/GammaCorrectionCommon.ush"

float4 LinearToGamma2(float4 Color) { return sqrt(Color); }
float3 LinearToGamma2(float3 Color) { return sqrt(Color); }
float2 LinearToGamma2(float2 Color) { return sqrt(Color); }
float  LinearToGamma2(float  Color) { return sqrt(Color); }

float4 Gamma2ToLinear(float4 Color) { return Color * Color; }
float3 Gamma2ToLinear(float3 Color) { return Color * Color; }
float2 Gamma2ToLinear(float2 Color) { return Color * Color; }
float  Gamma2ToLinear(float  Color) { return Color * Color; }

#if ENABLE_FP16
AH4 LinearToGamma2(AH4 Color) { return sqrt(Color); }
AH3 LinearToGamma2(AH3 Color) { return sqrt(Color); }
AH2 LinearToGamma2(AH2 Color) { return sqrt(Color); }
AH1 LinearToGamma2(AH1 Color) { return sqrt(Color); }

AH4 Gamma2ToLinear(AH4 Color) { return Color * Color; }
AH3 Gamma2ToLinear(AH3 Color) { return Color * Color; }
AH2 Gamma2ToLinear(AH2 Color) { return Color * Color; }
AH1 Gamma2ToLinear(AH1 Color) { return Color * Color; }
#endif

//-----------------------------------------------------------------

// only float3 ST2084ToLinear() is defined in GammaCorrectionCommon.ush
float ST2084ToLinear_F(float pq)
{
	const float m1 = 0.1593017578125; // = 2610. / 4096. * .25;
	const float m2 = 78.84375;        // = 2523. / 4096. *  128;
	const float c1 = 0.8359375;       // = 2392. / 4096. * 32 - 2413./4096.*32 + 1;
	const float c2 = 18.8515625;      // = 2413. / 4096. * 32;
	const float c3 = 18.6875;         // = 2392. / 4096. * 32;
	const float C = 10000.;

	float Np = pow(pq, 1. / m2);
	float L = Np - c1;
	L = max(0., L);
	L = L / (c2 - c3 * Np);
	L = pow(L, 1. / m1);
	float P = L * C;

	return P;
}
float  ST2084ToGamma2(float  pq) { return LinearToGamma2(ST2084ToLinear_F(pq)); }
float2 ST2084ToGamma2(float2 pq) { return LinearToGamma2(float2(ST2084ToLinear_F(pq.r), ST2084ToLinear_F(pq.g))); }
float3 ST2084ToGamma2(float3 pq) { return LinearToGamma2(ST2084ToLinear(pq)); }
float4 ST2084ToGamma2(float4 pq) { return LinearToGamma2(float4(ST2084ToLinear(pq.rgb), ST2084ToLinear_F(pq.a))); }

//-----------------------------------------------------------------

// Either 1000 or 2000 depending on UE4 Tonemapper enum, 
// should be provided by the engine
#if MAX_ODT_NITS_ENUM == 1
#define HDR_MAX_ODT_NITS 2000
#else 
#define HDR_MAX_ODT_NITS 1000
#endif

#define HDR_MAX_NITS     10000
#define HDR_MAX_NITS_INV 0.0001f

// matches white point in ST2084ToScRGB()
#define HDR_WHITE_POINT 80.0f

float3 Gamma2ToScRGB(float3 Color)
{
	const float3x3 Rec2020_2_sRGB = mul(XYZ_2_sRGB_MAT, Rec2020_2_XYZ_MAT);
	const float MaxODTNits = HDR_MAX_ODT_NITS;
	const float scRGBScale = MaxODTNits / HDR_WHITE_POINT;

	// Gamma2 -> Linear encoding
	float3 LinearColor_Rec2020 = Gamma2ToLinear(Color);

	// Rec2020 -> sRGB primaries
	float3 LinearColor_sRGB = mul(Rec2020_2_sRGB, LinearColor_Rec2020);

	// Linear_sRGB -> scRGB
	return LinearColor_sRGB * scRGBScale;
}

float3 scRGBToGamma2(float3 Color_scRGB)
{
	const float3x3 sRGB_2_Rec2020 = mul(XYZ_2_Rec2020_MAT, sRGB_2_XYZ_MAT);
	const float MaxODTNits = HDR_MAX_ODT_NITS;
	const float scRGBScale = MaxODTNits / HDR_WHITE_POINT;
	const float scRGBScaleInv = HDR_WHITE_POINT / MaxODTNits;

	// normalize to [0-1]
	Color_scRGB *= scRGBScaleInv;

	// convert primaries sRGB -> Rec2020 
	float3 Color_Rec2020 = mul(sRGB_2_Rec2020, Color_scRGB);

	// clamp negatives
	Color_Rec2020 = max(Color_Rec2020, 0); 

	// Gamma2-encode
	return LinearToGamma2(Color_Rec2020);
}

float3 LinearToScRGB(float3 LinearColor_Rec2020)
{
	const float3x3 Rec2020_2_sRGB = mul(XYZ_2_sRGB_MAT, Rec2020_2_XYZ_MAT);
	const float MaxODTNits = HDR_MAX_ODT_NITS;
	const float scRGBScale = MaxODTNits / HDR_WHITE_POINT;

	// Rec2020 -> sRGB primaries
	float3 LinearColor_sRGB = mul(Rec2020_2_sRGB, LinearColor_Rec2020);

	// Linear_sRGB -> scRGB
	return LinearColor_sRGB * scRGBScale;
}