ScriptableRenderPipeline/ScriptableRenderPipeline/Core/CoreRP/ShaderLibrary/Common.hlsl

#ifndef UNITY_COMMON_INCLUDED
#define UNITY_COMMON_INCLUDED

// Convention:

// Unity is Y up and left handed in world space
// Caution: When going from world space to view space, unity is right handed in view space and the determinant of the matrix is negative
// For cubemap capture (reflection probe) view space is still left handed (cubemap convention) and the determinant is positive.

// The lighting code assume that 1 Unity unit (1uu) == 1 meters.  This is very important regarding physically based light unit and inverse square attenuation

// space at the end of the variable name
// WS: world space
// VS: view space
// OS: object space
// CS: Homogenous clip spaces
// TS: tangent space
// TXS: texture space
// Example: NormalWS

// normalized / unormalized vector
// normalized direction are almost everywhere, we tag unormalized vector with un.
// Example: unL for unormalized light vector

// use capital letter for regular vector, vector are always pointing outward the current pixel position (ready for lighting equation)
// capital letter mean the vector is normalize, unless we put 'un' in front of it.
// V: View vector  (no eye vector)
// L: Light vector
// N: Normal vector
// H: Half vector

// Input/Outputs structs in PascalCase and prefixed by entry type
// struct AttributesDefault
// struct VaryingsDefault
// use input/output as variable name when using these structures

// Entry program name
// VertDefault
// FragDefault / FragForward / FragDeferred

// constant floating number written as 1.0  (not 1, not 1.0f, not 1.0h)

// uniform have _ as prefix + uppercase _LowercaseThenCamelCase

// Do not use "in", only "out" or "inout" as califier, no "inline" keyword either, useless.
// When declaring "out" argument of function, they are always last

// headers from ShaderLibrary do not include "common.hlsl", this should be included in the .shader using it (or Material.hlsl)

// All uniforms should be in contant buffer (nothing in the global namespace).
// The reason is that for compute shader we need to guarantee that the layout of CBs is consistent across kernels. Something that we can't control with the global namespace (uniforms get optimized out if not used, modifying the global CBuffer layout per kernel)

// Structure definition that are share between C# and hlsl.
// These structures need to be align on float4 to respect various packing rules from shader language. This mean that these structure need to be padded.
// Rules: When doing an array for constant buffer variables, we always use float4 to avoid any packing issue, particularly between compute shader and pixel shaders
// i.e don't use SetGlobalFloatArray or SetComputeFloatParams
// The array can be alias in hlsl. Exemple:
// uniform float4 packedArray[3];
// static float unpackedArray[12] = (float[12])packedArray;

// The function of the shader library are stateless, no uniform decalare in it.
// Any function that require an explicit precision, use float or half qualifier, when the function can support both, it use real (see below)
// If a function require to have both a half and a float version, then both need to be explicitly define
#ifndef real

#ifdef SHADER_API_MOBILE
#define real half
#define real2 half2
#define real3 half3
#define real4 half4

#define real2x2 half2x2
#define real2x3 half2x3
#define real3x2 half3x2
#define real3x3 half3x3
#define real3x4 half3x4
#define real4x3 half4x3
#define real4x4 half4x4

#define half min16float
#define half2 min16float2
#define half3 min16float3
#define half4 min16float4

#define half2x2 min16float2x2
#define half2x3 min16float2x3
#define half3x2 min16float3x2
#define half3x3 min16float3x3
#define half3x4 min16float3x4
#define half4x3 min16float4x3
#define half4x4 min16float4x4

#define REAL_MIN HALF_MIN
#define REAL_MAX HALF_MAX
#define TEMPLATE_1_REAL TEMPLATE_1_HALF
#define TEMPLATE_2_REAL TEMPLATE_2_HALF
#define TEMPLATE_3_REAL TEMPLATE_3_HALF

#else

#define real float
#define real2 float2
#define real3 float3
#define real4 float4

#define real2x2 float2x2
#define real2x3 float2x3
#define real3x2 float3x2
#define real3x3 float3x3
#define real3x4 float3x4
#define real4x3 float4x3
#define real4x4 float4x4

#define REAL_MIN FLT_MIN
#define REAL_MAX FLT_MAX
#define TEMPLATE_1_REAL TEMPLATE_1_FLT
#define TEMPLATE_2_REAL TEMPLATE_2_FLT
#define TEMPLATE_3_REAL TEMPLATE_3_FLT

#endif // SHADER_API_MOBILE

#endif // #ifndef real

// Target in compute shader are supported in 2018.2, for now define ours
// (Note only 45 and above support compute shader)
#ifdef  SHADER_STAGE_COMPUTE
#   ifndef SHADER_TARGET
#       if defined(SHADER_API_METAL) || defined(SHADER_API_VULKAN)
#       define SHADER_TARGET 45
#       else
#       define SHADER_TARGET 50
#       endif
#   endif
#endif

// Include language header
#if defined(SHADER_API_D3D11)
#include "API/D3D11.hlsl"
#elif defined(SHADER_API_PSSL)
#include "API/PSSL.hlsl"
#elif defined(SHADER_API_XBOXONE)
#include "API/XBoxOne.hlsl"
#elif defined(SHADER_API_METAL)
#include "API/Metal.hlsl"
#elif defined(SHADER_API_VULKAN)
#include "API/Vulkan.hlsl"
#elif defined(SHADER_API_GLCORE)
#include "API/GLCore.hlsl"
#elif defined(SHADER_API_GLES3)
#include "API/GLES3.hlsl"
#elif defined(SHADER_API_GLES)
#include "API/GLES2.hlsl"
#else
#error unsupported shader api
#endif
#include "API/Validate.hlsl"

#include "Macros.hlsl"
#include "Random.hlsl"

// ----------------------------------------------------------------------------
// Common intrinsic (general implementation of intrinsic available on some platform)
// ----------------------------------------------------------------------------

// Error on GLES2 undefined functions
#ifdef SHADER_API_GLES
#define BitFieldExtract ERROR_ON_UNSUPPORTED_FUNC(BitFieldExtract)
#define IsBitSet ERROR_ON_UNSUPPORTED_FUNC(IsBitSet)
#define SetBit ERROR_ON_UNSUPPORTED_FUNC(SetBit)
#define ClearBit ERROR_ON_UNSUPPORTED_FUNC(ClearBit)
#define ToggleBit ERROR_ON_UNSUPPORTED_FUNC(ToggleBit)
#define FastMulBySignOfNegZero ERROR_ON_UNSUPPORTED_FUNC(FastMulBySignOfNegZero)
#define LODDitheringTransition ERROR_ON_UNSUPPORTED_FUNC(LODDitheringTransition)
#endif

#if !defined(SHADER_API_GLES)

#ifndef INTRINSIC_BITFIELD_EXTRACT
// Unsigned integer bit field extraction.
// Note that the intrinsic itself generates a vector instruction.
// Wrap this function with WaveReadFirstLane() to get scalar output.
uint BitFieldExtract(uint data, uint offset, uint numBits)
{
    uint mask = (1u << numBits) - 1u;
    return (data >> offset) & mask;
}
#endif // INTRINSIC_BITFIELD_EXTRACT

#ifndef INTRINSIC_BITFIELD_EXTRACT_SIGN_EXTEND
// Integer bit field extraction with sign extension.
// Note that the intrinsic itself generates a vector instruction.
// Wrap this function with WaveReadFirstLane() to get scalar output.
int BitFieldExtractSignExtend(int data, uint offset, uint numBits)
{
    int  shifted = data >> offset;      // Sign-extending (arithmetic) shift
    int  signBit = shifted & (1u << (numBits - 1u));
    uint mask    = (1u << numBits) - 1u;

    return -signBit | (shifted & mask); // Use 2-complement for negation to replicate the sign bit
}
#endif // INTRINSIC_BITFIELD_EXTRACT_SIGN_EXTEND

#ifndef INTRINSIC_BITFIELD_INSERT
// Inserts the bits indicated by 'mask' from 'src' into 'dst'.
uint BitFieldInsert(uint mask, uint src, uint dst)
{
    return (src & mask) | (dst & ~mask);
}
#endif // INTRINSIC_BITFIELD_INSERT

bool IsBitSet(uint data, uint offset)
{
    return BitFieldExtract(data, offset, 1u) != 0;
}

void SetBit(inout uint data, uint offset)
{
    data |= 1u << offset;
}

void ClearBit(inout uint data, uint offset)
{
    data &= ~(1u << offset);
}

void ToggleBit(inout uint data, uint offset)
{
    data ^= 1u << offset;
}

#endif


#ifndef INTRINSIC_WAVEREADFIRSTLANE
    // Warning: for correctness, the argument's value must be the same across all lanes of the wave.
    TEMPLATE_1_REAL(WaveReadFirstLane, scalarValue, return scalarValue)
    TEMPLATE_1_INT(WaveReadFirstLane, scalarValue, return scalarValue)
#endif

#ifndef INTRINSIC_MUL24
    TEMPLATE_2_INT(Mul24, a, b, return a * b)
#endif // INTRINSIC_MUL24

#ifndef INTRINSIC_MAD24
    TEMPLATE_3_INT(Mad24, a, b, c, return a * b + c)
#endif // INTRINSIC_MAD24

#ifndef INTRINSIC_MINMAX3
    TEMPLATE_3_REAL(Min3, a, b, c, return min(min(a, b), c))
    TEMPLATE_3_INT(Min3, a, b, c, return min(min(a, b), c))
    TEMPLATE_3_REAL(Max3, a, b, c, return max(max(a, b), c))
    TEMPLATE_3_INT(Max3, a, b, c, return max(max(a, b), c))
#endif // INTRINSIC_MINMAX3

TEMPLATE_SWAP(Swap) // Define a Swap(a, b) function for all types

#define CUBEMAPFACE_POSITIVE_X 0
#define CUBEMAPFACE_NEGATIVE_X 1
#define CUBEMAPFACE_POSITIVE_Y 2
#define CUBEMAPFACE_NEGATIVE_Y 3
#define CUBEMAPFACE_POSITIVE_Z 4
#define CUBEMAPFACE_NEGATIVE_Z 5

#ifndef INTRINSIC_CUBEMAP_FACE_ID
float CubeMapFaceID(float3 dir)
{
    float faceID;

    if (abs(dir.z) >= abs(dir.x) && abs(dir.z) >= abs(dir.y))
    {
        faceID = (dir.z < 0.0) ? CUBEMAPFACE_NEGATIVE_Z : CUBEMAPFACE_POSITIVE_Z;
    }
    else if (abs(dir.y) >= abs(dir.x))
    {
        faceID = (dir.y < 0.0) ? CUBEMAPFACE_NEGATIVE_Y : CUBEMAPFACE_POSITIVE_Y;
    }
    else
    {
        faceID = (dir.x < 0.0) ? CUBEMAPFACE_NEGATIVE_X : CUBEMAPFACE_POSITIVE_X;
    }

    return faceID;
}
#endif // INTRINSIC_CUBEMAP_FACE_ID

// Intrinsic isnan can't be used because it require /Gic to be enabled on fxc that we can't do. So use AnyIsNan instead
bool IsNan(float n)
{
    return (n < 0.0 || n > 0.0 || n == 0.0) ? false : true;
}

bool AnyIsNan(float2 v)
{
    return (IsNan(v.x) || IsNan(v.y));
}

bool AnyIsNan(float3 v)
{
    return (IsNan(v.x) || IsNan(v.y) || IsNan(v.z));
}

bool AnyIsNan(float4 v)
{
    return (IsNan(v.x) || IsNan(v.y) || IsNan(v.z) || IsNan(v.w));
}

// ----------------------------------------------------------------------------
// Common math functions
// ----------------------------------------------------------------------------

real DegToRad(real deg)
{
    return deg * (PI / 180.0);
}

real RadToDeg(real rad)
{
    return rad * (180.0 / PI);
}

// Square functions for cleaner code
TEMPLATE_1_REAL(Sq, x, return x * x)
TEMPLATE_1_INT(Sq, x, return x * x)

bool IsPower2(uint x)
{
    return (x & (x - 1)) == 0;
}

// Input [0, 1] and output [0, PI/2]
// 9 VALU
real FastACosPos(real inX)
{
    real x = abs(inX);
    real res = (0.0468878 * x + -0.203471) * x + 1.570796; // p(x)
    res *= sqrt(1.0 - x);

    return res;
}

// Ref: https://seblagarde.wordpress.com/2014/12/01/inverse-trigonometric-functions-gpu-optimization-for-amd-gcn-architecture/
// Input [-1, 1] and output [0, PI]
// 12 VALU
real FastACos(real inX)
{
    real res = FastACosPos(inX);

    return (inX >= 0) ? res : PI - res; // Undo range reduction
}

// Same cost as Acos + 1 FR
// Same error
// input [-1, 1] and output [-PI/2, PI/2]
real FastASin(real x)
{
    return HALF_PI - FastACos(x);
}

// max absolute error 1.3x10^-3
// Eberly's odd polynomial degree 5 - respect bounds
// 4 VGPR, 14 FR (10 FR, 1 QR), 2 scalar
// input [0, infinity] and output [0, PI/2]
real FastATanPos(real x)
{
    real t0 = (x < 1.0) ? x : 1.0 / x;
    real t1 = t0 * t0;
    real poly = 0.0872929;
    poly = -0.301895 + poly * t1;
    poly = 1.0 + poly * t1;
    poly = poly * t0;
    return (x < 1.0) ? poly : HALF_PI - poly;
}

#if (SHADER_TARGET >= 45)
uint FastLog2(uint x)
{
    return firstbithigh(x);
}
#endif

// 4 VGPR, 16 FR (12 FR, 1 QR), 2 scalar
// input [-infinity, infinity] and output [-PI/2, PI/2]
real FastATan(real x)
{
    real t0 = FastATanPos(abs(x));
    return (x < 0.0) ? -t0 : t0;
}

// Using pow often result to a warning like this
// "pow(f, e) will not work for negative f, use abs(f) or conditionally handle negative values if you expect them"
// PositivePow remove this warning when you know the value is positive or 0 and avoid inf/NAN.
// Note: https://msdn.microsoft.com/en-us/library/windows/desktop/bb509636(v=vs.85).aspx pow(0, >0) == 0
TEMPLATE_2_REAL(PositivePow, base, power, return pow(abs(base), power))

// Composes a floating point value with the magnitude of 'x' and the sign of 's'.
// See the comment about FastSign() below.
float CopySign(float x, float s, bool ignoreNegZero = true)
{
#if !defined(SHADER_API_GLES)
    if (ignoreNegZero)
    {
        return (s >= 0) ? abs(x) : -abs(x);
    }
    else
    {
        uint negZero = 0x80000000u;
        uint signBit = negZero & asuint(s);
        return asfloat(BitFieldInsert(negZero, signBit, asuint(x)));
    }
#else
    return (s >= 0) ? abs(x) : -abs(x);
#endif
}

// Returns -1 for negative numbers and 1 for positive numbers.
// 0 can be handled in 2 different ways.
// The IEEE floating point standard defines 0 as signed: +0 and -0.
// However, mathematics typically treats 0 as unsigned.
// Therefore, we treat -0 as +0 by default: FastSign(+0) = FastSign(-0) = 1.
// If (ignoreNegZero = false), FastSign(-0, false) = -1.
// Note that the sign() function in HLSL implements signum, which returns 0 for 0.
float FastSign(float s, bool ignoreNegZero = true)
{
    return CopySign(1.0, s, ignoreNegZero);
}

// Orthonormalizes the tangent frame using the Gram-Schmidt process.
// We assume that both the tangent and the normal are normalized.
// Returns the new tangent (the normal is unaffected).
real3 Orthonormalize(real3 tangent, real3 normal)
{
    return normalize(tangent - dot(tangent, normal) * normal);
}

// Same as smoothstep except it assume 0, 1 interval for x
real Smoothstep01(real x)
{
    return x * x * (3.0 - (2.0 * x));
}

real Pow4(real x)
{
    return (x * x) * (x * x);
}

// ----------------------------------------------------------------------------
// Texture utilities
// ----------------------------------------------------------------------------

float ComputeTextureLOD(float2 uv)
{
    float2 ddx_ = ddx(uv);
    float2 ddy_ = ddy(uv);
    float d = max(dot(ddx_, ddx_), dot(ddy_, ddy_));

    return max(0.5 * log2(d), 0.0);
}

// x contains width, w contains height
float ComputeTextureLOD(float2 uv, float2 texelSize)
{
    uv *= texelSize;

    return ComputeTextureLOD(uv);
}

uint GetMipCount(Texture2D tex)
{
#if defined(SHADER_API_D3D11) || defined(SHADER_API_D3D12) || defined(SHADER_API_D3D11_9X) || defined(SHADER_API_XBOXONE) || defined(SHADER_API_PSSL)
    #define MIP_COUNT_SUPPORTED 1
#endif
#if (defined(SHADER_API_OPENGL) || defined(SHADER_API_VULKAN)) && !defined(SHADER_STAGE_COMPUTE)
    // OpenGL only supports textureSize for width, height, depth
    // textureQueryLevels (GL_ARB_texture_query_levels) needs OpenGL 4.3 or above and doesn't compile in compute shaders
    // tex.GetDimensions converted to textureQueryLevels
    #define MIP_COUNT_SUPPORTED 1
#endif
    // Metal doesn't support high enough OpenGL version

#if defined(MIP_COUNT_SUPPORTED)
    uint width, height, depth, mipCount;
    width = height = depth = mipCount = 0;
    tex.GetDimensions(width, height, depth, mipCount);
    return mipCount;
#else
    return 0;
#endif
}

// ----------------------------------------------------------------------------
// Texture format sampling
// ----------------------------------------------------------------------------

float2 DirectionToLatLongCoordinate(float3 unDir)
{
    float3 dir = normalize(unDir);
    // coordinate frame is (-Z, X) meaning negative Z is primary axis and X is secondary axis.
    return float2(1.0 - 0.5 * INV_PI * atan2(dir.x, -dir.z), asin(dir.y) * INV_PI + 0.5);
}

float3 LatlongToDirectionCoordinate(float2 coord)
{
    float theta = coord.y * PI;
    float phi = (coord.x * 2.f * PI - PI*0.5f);

    float cosTheta = cos(theta);
    float sinTheta = sqrt(1.0 - min(1.0, cosTheta*cosTheta));
    float cosPhi = cos(phi);
    float sinPhi = sin(phi);

    float3 direction = float3(sinTheta*cosPhi, cosTheta, sinTheta*sinPhi);
    direction.xy *= -1.0;
    return direction;
}

// ----------------------------------------------------------------------------
// Depth encoding/decoding
// ----------------------------------------------------------------------------

// Z buffer to linear 0..1 depth (0 at near plane, 1 at far plane).
// Does not correctly handle oblique view frustums.
// zBufferParam = { (f-n)/n, 1, (f-n)/n*f, 1/f }
float Linear01DepthFromNear(float depth, float4 zBufferParam)
{
    return 1.0 / (zBufferParam.x + zBufferParam.y / depth);
}

// Z buffer to linear 0..1 depth (0 at camera position, 1 at far plane).
// Does not correctly handle oblique view frustums.
// zBufferParam = { (f-n)/n, 1, (f-n)/n*f, 1/f }
float Linear01Depth(float depth, float4 zBufferParam)
{
    return 1.0 / (zBufferParam.x * depth + zBufferParam.y);
}

// Z buffer to linear depth.
// Does not correctly handle oblique view frustums.
// zBufferParam = { (f-n)/n, 1, (f-n)/n*f, 1/f }
float LinearEyeDepth(float depth, float4 zBufferParam)
{
    return 1.0 / (zBufferParam.z * depth + zBufferParam.w);
}

// Z buffer to linear depth.
// Correctly handles oblique view frustums. Only valid for projection matrices!
// Ref: An Efficient Depth Linearization Method for Oblique View Frustums, Eq. 6.
float LinearEyeDepth(float2 positionNDC, float deviceDepth, float4 invProjParam)
{
    float4 positionCS = float4(positionNDC * 2.0 - 1.0, deviceDepth, 1.0);
    float  viewSpaceZ = rcp(dot(positionCS, invProjParam));
    // The view space uses a right-handed coordinate system.
    return -viewSpaceZ;
}

// Z buffer to linear depth.
// Correctly handles oblique view frustums.
// Typically, this is the cheapest variant, provided you've already computed 'positionWS'.
float LinearEyeDepth(float3 positionWS, float4x4 viewProjMatrix)
{
    return mul(viewProjMatrix, float4(positionWS, 1.0)).w;
}

// 'z' is the view space Z position (linear depth).
// saturate(z) the output of the function to clamp them to the [0, 1] range.
// d = log2(c * (z - n) + 1) / log2(c * (f - n) + 1)
//   = log2(c * (z - n + 1/c)) / log2(c * (f - n) + 1)
//   = log2(c) / log2(c * (f - n) + 1) + log2(z - (n - 1/c)) / log2(c * (f - n) + 1)
//   = E + F * log2(z - G)
// encodingParams = { E, F, G, 0 }
float EncodeLogarithmicDepthGeneralized(float z, float4 encodingParams)
{
    // Use max() to avoid NaNs.
    return encodingParams.x + encodingParams.y * log2(max(0, z - encodingParams.z));
}

// 'd' is the logarithmically encoded depth value.
// saturate(d) to clamp the output of the function to the [n, f] range.
// z = 1/c * (pow(c * (f - n) + 1, d) - 1) + n
//   = 1/c * pow(c * (f - n) + 1, d) + n - 1/c
//   = L * pow(M, d) + N
// decodingParams = { L, M, N, 0 }
// Graph: https://www.desmos.com/calculator/qrtatrlrba
float DecodeLogarithmicDepthGeneralized(float d, float4 decodingParams)
{
    // Use abs() to avoid the compiler warning.
    return decodingParams.x * pow(abs(decodingParams.y), d) + decodingParams.z;
}

// 'z' is the view-space Z position (linear depth).
// saturate(z) the output of the function to clamp them to the [0, 1] range.
// encodingParams = { n, log2(f/n), 1/n, 1/log2(f/n) }
// This is an optimized version of EncodeLogarithmicDepthGeneralized() for (c = 2).
float EncodeLogarithmicDepth(float z, float4 encodingParams)
{
    // Use max() to avoid NaNs.
    return log2(max(0, z * encodingParams.z)) * encodingParams.w;
}

// 'd' is the logarithmically encoded depth value.
// saturate(d) to clamp the output of the function to the [n, f] range.
// encodingParams = { n, log2(f/n), 1/n, 1/log2(f/n) }
// This is an optimized version of DecodeLogarithmicDepthGeneralized() for (c = 2).
// Graph: https://www.desmos.com/calculator/qrtatrlrba
float DecodeLogarithmicDepth(float d, float4 encodingParams)
{
    return encodingParams.x * exp2(d * encodingParams.y);
}

// ----------------------------------------------------------------------------
// Space transformations
// ----------------------------------------------------------------------------

static const float3x3 k_identity3x3 = {1, 0, 0,
                                       0, 1, 0,
                                       0, 0, 1};

static const float4x4 k_identity4x4 = {1, 0, 0, 0,
                                       0, 1, 0, 0,
                                       0, 0, 1, 0,
                                       0, 0, 0, 1};

float4 ComputeClipSpacePosition(float2 positionNDC, float deviceDepth)
{
    float4 positionCS = float4(positionNDC * 2.0 - 1.0, deviceDepth, 1.0);

#if UNITY_UV_STARTS_AT_TOP
    // Our world space, view space, screen space and NDC space are Y-up.
    // Our clip space is flipped upside-down due to poor legacy Unity design.
    // The flip is baked into the projection matrix, so we only have to flip
    // manually when going from CS to NDC and back.
    positionCS.y = -positionCS.y;
#endif

    return positionCS;
}

// Use case examples:
// (position = positionCS) => (clipSpaceTransform = use default)
// (position = positionVS) => (clipSpaceTransform = UNITY_MATRIX_P)
// (position = positionWS) => (clipSpaceTransform = UNITY_MATRIX_VP)
float4 ComputeClipSpacePosition(float3 position, float4x4 clipSpaceTransform = k_identity4x4)
{
    return mul(clipSpaceTransform, float4(position, 1.0));
}

// Use case examples:
// (position = positionCS) => (clipSpaceTransform = use default)
// (position = positionVS) => (clipSpaceTransform = UNITY_MATRIX_P)
// (position = positionWS) => (clipSpaceTransform = UNITY_MATRIX_VP)
float3 ComputeNormalizedDeviceCoordinatesWithZ(float3 position, float4x4 clipSpaceTransform = k_identity4x4)
{
    float4 positionCS = ComputeClipSpacePosition(position, clipSpaceTransform);

#if UNITY_UV_STARTS_AT_TOP
    // Our world space, view space, screen space and NDC space are Y-up.
    // Our clip space is flipped upside-down due to poor legacy Unity design.
    // The flip is baked into the projection matrix, so we only have to flip
    // manually when going from CS to NDC and back.
    positionCS.y = -positionCS.y;
#endif

    positionCS *= rcp(positionCS.w);
    positionCS.xy = positionCS.xy * 0.5 + 0.5;

    return positionCS.xyz;
}

// Use case examples:
// (position = positionCS) => (clipSpaceTransform = use default)
// (position = positionVS) => (clipSpaceTransform = UNITY_MATRIX_P)
// (position = positionWS) => (clipSpaceTransform = UNITY_MATRIX_VP)
float2 ComputeNormalizedDeviceCoordinates(float3 position, float4x4 clipSpaceTransform = k_identity4x4)
{
    return ComputeNormalizedDeviceCoordinatesWithZ(position, clipSpaceTransform).xy;
}

float3 ComputeViewSpacePosition(float2 positionNDC, float deviceDepth, float4x4 invProjMatrix)
{
    float4 positionCS = ComputeClipSpacePosition(positionNDC, deviceDepth);
    float4 positionVS = mul(invProjMatrix, positionCS);
    // The view space uses a right-handed coordinate system.
    positionVS.z = -positionVS.z;
    return positionVS.xyz / positionVS.w;
}

float3 ComputeWorldSpacePosition(float2 positionNDC, float deviceDepth, float4x4 invViewProjMatrix)
{
    float4 positionCS  = ComputeClipSpacePosition(positionNDC, deviceDepth);
    float4 hpositionWS = mul(invViewProjMatrix, positionCS);
    return hpositionWS.xyz / hpositionWS.w;
}

// ----------------------------------------------------------------------------
// PositionInputs
// ----------------------------------------------------------------------------

struct PositionInputs
{
    float3 positionWS;  // World space position (could be camera-relative)
    float2 positionNDC; // Normalized screen coordinates within the viewport    : [0, 1) (with the half-pixel offset)
    uint2  positionSS;  // Screen space pixel coordinates                       : [0, NumPixels)
    uint2  tileCoord;   // Screen tile coordinates                              : [0, NumTiles)
    float  deviceDepth; // Depth from the depth buffer                          : [0, 1] (typically reversed)
    float  linearDepth; // View space Z coordinate                              : [Near, Far]
};

// This function is use to provide an easy way to sample into a screen texture, either from a pixel or a compute shaders.
// This allow to easily share code.
// If a compute shader call this function positionSS is an integer usually calculate like: uint2 positionSS = groupId.xy * BLOCK_SIZE + groupThreadId.xy
// else it is current unormalized screen coordinate like return by SV_Position
PositionInputs GetPositionInput(float2 positionSS, float2 invScreenSize, uint2 tileCoord)   // Specify explicit tile coordinates so that we can easily make it lane invariant for compute evaluation.
{
    PositionInputs posInput;
    ZERO_INITIALIZE(PositionInputs, posInput);

    posInput.positionNDC = positionSS;
#if SHADER_STAGE_COMPUTE
    // In case of compute shader an extra half offset is added to the screenPos to shift the integer position to pixel center.
    posInput.positionNDC.xy += float2(0.5, 0.5);
#endif
    posInput.positionNDC *= invScreenSize;

    posInput.positionSS = uint2(positionSS);
    posInput.tileCoord = tileCoord;

    return posInput;
}

PositionInputs GetPositionInput(float2 positionSS, float2 invScreenSize)
{
    return GetPositionInput(positionSS, invScreenSize, uint2(0, 0));
}

// From forward
// deviceDepth and linearDepth come directly from .zw of SV_Position
PositionInputs GetPositionInput(float2 positionSS, float2 invScreenSize, float deviceDepth, float linearDepth, float3 positionWS, uint2 tileCoord)
{
    PositionInputs posInput = GetPositionInput(positionSS, invScreenSize, tileCoord);
    posInput.deviceDepth = deviceDepth;
    posInput.linearDepth = linearDepth;
    posInput.positionWS  = positionWS;

    return posInput;
}

PositionInputs GetPositionInput(float2 positionSS, float2 invScreenSize, float deviceDepth, float linearDepth, float3 positionWS)
{
    return GetPositionInput(positionSS, invScreenSize, deviceDepth, linearDepth, positionWS, uint2(0, 0));
}

// From deferred or compute shader
// depth must be the depth from the raw depth buffer. This allow to handle all kind of depth automatically with the inverse view projection matrix.
// For information. In Unity Depth is always in range 0..1 (even on OpenGL) but can be reversed.
PositionInputs GetPositionInput(float2 positionSS, float2 invScreenSize, float deviceDepth, float4x4 invViewProjMatrix, float4x4 viewProjMatrix, uint2 tileCoord)
{
    PositionInputs posInput = GetPositionInput(positionSS, invScreenSize, tileCoord);
    posInput.deviceDepth = deviceDepth;
    posInput.positionWS  = ComputeWorldSpacePosition(posInput.positionNDC, deviceDepth, invViewProjMatrix);

    // The compiler should optimize this (less expensive than reconstruct depth VS from depth buffer)
    posInput.linearDepth = mul(viewProjMatrix, float4(posInput.positionWS, 1.0)).w;

    return posInput;
}

PositionInputs GetPositionInput(float2 positionSS, float2 invScreenSize, float deviceDepth, float4x4 invViewProjMatrix, float4x4 viewProjMatrix)
{
    return GetPositionInput(positionSS, invScreenSize, deviceDepth, invViewProjMatrix, viewProjMatrix, uint2(0, 0));
}

// The view direction 'V' points towards the camera.
// 'depthOffsetVS' is always applied in the opposite direction (-V).
void ApplyDepthOffsetPositionInput(float3 V, float depthOffsetVS, float4x4 viewProjMatrix, inout PositionInputs posInput)
{
    posInput.positionWS += depthOffsetVS * (-V);

    float4 positionCS    = mul(viewProjMatrix, float4(posInput.positionWS, 1.0));
    posInput.linearDepth = positionCS.w;
    posInput.deviceDepth = positionCS.z / positionCS.w;
}

// ----------------------------------------------------------------------------
// Misc utilities
// ----------------------------------------------------------------------------

// Normalize that account for vectors with zero length
real3 SafeNormalize(real3 inVec)
{
    real dp3 = max(REAL_MIN, dot(inVec, inVec));
    return inVec * rsqrt(dp3);
}

// Generates a triangle in homogeneous clip space, s.t.
// v0 = (-1, -1, 1), v1 = (3, -1, 1), v2 = (-1, 3, 1).
float2 GetFullScreenTriangleTexCoord(uint vertexID)
{
#if UNITY_UV_STARTS_AT_TOP
    return float2((vertexID << 1) & 2, 1.0 - (vertexID & 2));
#else
    return float2((vertexID << 1) & 2, vertexID & 2);
#endif
}

float4 GetFullScreenTriangleVertexPosition(uint vertexID, float z = UNITY_NEAR_CLIP_VALUE)
{
    float2 uv = float2((vertexID << 1) & 2, vertexID & 2);
    return float4(uv * 2.0 - 1.0, z, 1.0);
}

#if !defined(SHADER_API_GLES)

// LOD dithering transition helper
// LOD0 must use this function with ditherFactor 1..0
// LOD1 must use this function with ditherFactor 0..1
void LODDitheringTransition(uint2 positionSS, float ditherFactor)
{
    // Generate a spatially varying pattern.
    // Unfortunately, varying the pattern with time confuses the TAA, increasing the amount of noise.
    float p = GenerateHashedRandomFloat(positionSS);

    // We want to have a symmetry between 0..0.5 ditherFactor and 0.5..1 so no pixels are transparent during the transition
    // this is handled by this test which reverse the pattern
    p = (ditherFactor >= 0.5) ? p : 1 - p;
    clip(ditherFactor - p);
}

#endif


#endif // UNITY_COMMON_INCLUDED