ml.hlsli

// © 2021 NVIDIA Corporation

#ifndef ML_HLSLI
#define ML_HLSLI

#define compiletime

#ifndef __cplusplus
    #define ML_Unused( x )
    #define ML_INLINE
    #define ML_OUT( T )                            out T
    #define ML_INOUT( T )                          inout T
#else
    #define ML_OUT( T )                            T&
    #define ML_INOUT( T )                          T&
#endif

//===========================================================================================================================
// Settings
//===========================================================================================================================

#define ML_WINDOW_ORIGIN_OGL                       0

// Math
#define ML_SIGN_DEFAULT                            ML_SIGN_FAST
#define ML_SQRT_DEFAULT                            ML_SQRT_SAFE
#define ML_RSQRT_DEFAULT                           ML_POSITIVE_RSQRT_ACCURATE_SAFE
#define ML_POSITIVE_RCP_DEFAULT                    ML_POSITIVE_RCP_ACCURATE_SAFE
#define ML_SMALL_EPS                               1e-15f
#define ML_EPS                                     1e-6f

// BRDF
#define ML_SPECULAR_DOMINANT_DIRECTION_DEFAULT     ML_SPECULAR_DOMINANT_DIRECTION_APPROX
#define ML_RF0_DIELECTRICS                         0.04f
#define ML_GTR_GAMMA                               1.5f
#define ML_VNDF_VERSION                            3

// Text
#define ML_TEXT_DIGIT_FORMAT                       10000
#define ML_TEXT_WITH_NICE_ONE_PIXEL_BACKGROUND     0

// Other
#define ML_RNG_NEXT_MODE                           ML_RNG_HASH
#define ML_RNG_FLOAT01_MODE                        ML_RNG_MANTISSA_BITS
#define ML_BAYER_DEFAULT                           ML_BAYER_REVERSEBITS

#ifdef ML_NAMESPACE
namespace ml
{
#endif

//=======================================================================================================================
// MATH
//=======================================================================================================================

namespace Math
{
    // Pi
    #define _Pi( x ) radians( x * 180.0f )

    ML_INLINE float Pi( float x )
    { return _Pi( x ); }

    ML_INLINE float2 Pi( float2 x )
    { return _Pi( x ); }

    ML_INLINE float3 Pi( float3 x )
    { return _Pi( x ); }

    ML_INLINE float4 Pi( float4 x )
    { return _Pi( x ); }

    // Radians to degrees
    #define _RadToDeg( x ) ( x * 180.0f / Pi( 1.0f ) )

    ML_INLINE float RadToDeg( float x )
    { return _RadToDeg( x ); }

    ML_INLINE float2 RadToDeg( float2 x )
    { return _RadToDeg( x ); }

    ML_INLINE float3 RadToDeg( float3 x )
    { return _RadToDeg( x ); }

    ML_INLINE float4 RadToDeg( float4 x )
    { return _RadToDeg( x ); }

    // Degrees to radians
    #define _DegToRad( x ) ( x * Pi( 1.0f ) / 180.0f )

    ML_INLINE float DegToRad( float x )
    { return _DegToRad( x ); }

    ML_INLINE float2 DegToRad( float2 x )
    { return _DegToRad( x ); }

    ML_INLINE float3 DegToRad( float3 x )
    { return _DegToRad( x ); }

    ML_INLINE float4 DegToRad( float4 x )
    { return _DegToRad( x ); }

    // LinearStep
    #define _LinearStep( a, b, x ) saturate( ( x - a ) / ( b - a ) )

    ML_INLINE float LinearStep( float a, float b, float x )
    { return _LinearStep( a, b, x ); }

    ML_INLINE float2 LinearStep( float2 a, float2 b, float2 x )
    { return _LinearStep( a, b, x ); }

    ML_INLINE float3 LinearStep( float3 a, float3 b, float3 x )
    { return _LinearStep( a, b, x ); }

    ML_INLINE float4 LinearStep( float4 a, float4 b, float4 x )
    { return _LinearStep( a, b, x ); }

    // SmoothStep
    #define _SmoothStep01( x ) ( x * x * ( 3.0f - x * 2.0f ) )

    ML_INLINE float SmoothStep01( float x )
    { return _SmoothStep01( saturate( x ) ); }

    ML_INLINE float2 SmoothStep01( float2 x )
    { return _SmoothStep01( saturate( x ) ); }

    ML_INLINE float3 SmoothStep01( float3 x )
    { return _SmoothStep01( saturate( x ) ); }

    ML_INLINE float4 SmoothStep01( float4 x )
    { return _SmoothStep01( saturate( x ) ); }

    ML_INLINE float SmoothStep( float a, float b, float x )
    { x = _LinearStep( a, b, x ); return _SmoothStep01( x ); }

    ML_INLINE float2 SmoothStep( float2 a, float2 b, float2 x )
    { x = _LinearStep( a, b, x ); return _SmoothStep01( x ); }

    ML_INLINE float3 SmoothStep( float3 a, float3 b, float3 x )
    { x = _LinearStep( a, b, x ); return _SmoothStep01( x ); }

    ML_INLINE float4 SmoothStep( float4 a, float4 b, float4 x )
    { x = _LinearStep( a, b, x ); return _SmoothStep01( x ); }

    // SmootherStep
    // https://en.wikipedia.org/wiki/Smoothstep
    #define _SmootherStep01( x ) ( x * x * x * ( x * ( x * 6.0f - 15.0f ) + 10.0f ) )

    ML_INLINE float SmootherStep( float a, float b, float x )
    { x = _LinearStep( a, b, x ); return _SmootherStep01( x ); }

    ML_INLINE float2 SmootherStep( float2 a, float2 b, float2 x )
    { x = _LinearStep( a, b, x ); return _SmootherStep01( x ); }

    ML_INLINE float3 SmootherStep( float3 a, float3 b, float3 x )
    { x = _LinearStep( a, b, x ); return _SmootherStep01( x ); }

    ML_INLINE float4 SmootherStep( float4 a, float4 b, float4 x )
    { x = _LinearStep( a, b, x ); return _SmootherStep01( x ); }

    // Sign
    #define ML_SIGN_BUILTIN 0
    #define ML_SIGN_FAST 1
    #define _Sign( x ) ( step( 0.0f, x ) * 2.0f - 1.0f )

    ML_INLINE float Sign( float x, compiletime const uint mode = ML_SIGN_DEFAULT )
    { return mode == ML_SIGN_FAST ? _Sign( x ) : sign( x ); }

    ML_INLINE float2 Sign( float2 x, compiletime const uint mode = ML_SIGN_DEFAULT )
    { return mode == ML_SIGN_FAST ? _Sign( x ) : sign( x ); }

    ML_INLINE float3 Sign( float3 x, compiletime const uint mode = ML_SIGN_DEFAULT )
    { return mode == ML_SIGN_FAST ? _Sign( x ) : sign( x ); }

    ML_INLINE float4 Sign( float4 x, compiletime const uint mode = ML_SIGN_DEFAULT )
    { return mode == ML_SIGN_FAST ? _Sign( x ) : sign( x ); }

    // Pow
    ML_INLINE float Pow( float x, float y )
    { return pow( abs( x ), y ); }

    ML_INLINE float2 Pow( float2 x, float y )
    { return pow( abs( x ), y ); }

    ML_INLINE float2 Pow( float2 x, float2 y )
    { return pow( abs( x ), y ); }

    ML_INLINE float3 Pow( float3 x, float y )
    { return pow( abs( x ), y ); }

    ML_INLINE float3 Pow( float3 x, float3 y )
    { return pow( abs( x ), y ); }

    ML_INLINE float4 Pow( float4 x, float y )
    { return pow( abs( x ), y ); }

    ML_INLINE float4 Pow( float4 x, float4 y )
    { return pow( abs( x ), y ); }

    // Pow for values in range [0; 1]
    ML_INLINE float Pow01( float x, float y )
    { return pow( saturate( x ), y ); }

    ML_INLINE float2 Pow01( float2 x, float y )
    { return pow( saturate( x ), y ); }

    ML_INLINE float2 Pow01( float2 x, float2 y )
    { return pow( saturate( x ), y ); }

    ML_INLINE float3 Pow01( float3 x, float y )
    { return pow( saturate( x ), y ); }

    ML_INLINE float3 Pow01( float3 x, float3 y )
    { return pow( saturate( x ), y ); }

    ML_INLINE float4 Pow01( float4 x, float y )
    { return pow( saturate( x ), y ); }

    ML_INLINE float4 Pow01( float4 x, float4 y )
    { return pow( saturate( x ), y ); }

    // Sqrt
    #define ML_SQRT_BUILTIN 0
    #define ML_SQRT_SAFE 1

    ML_INLINE float Sqrt( float x, compiletime const uint mode = ML_SQRT_DEFAULT )
    { return sqrt( mode == ML_SQRT_SAFE ? max( x, 0.0f ) : x ); }

    ML_INLINE float2 Sqrt( float2 x, compiletime const uint mode = ML_SQRT_DEFAULT )
    { return sqrt( mode == ML_SQRT_SAFE ? max( x, 0.0f ) : x ); }

    ML_INLINE float3 Sqrt( float3 x, compiletime const uint mode = ML_SQRT_DEFAULT )
    { return sqrt( mode == ML_SQRT_SAFE ? max( x, 0.0f ) : x ); }

    ML_INLINE float4 Sqrt( float4 x, compiletime const uint mode = ML_SQRT_DEFAULT )
    { return sqrt( mode == ML_SQRT_SAFE ? max( x, 0.0f ) : x ); }

    // Sqrt for values in range [0; 1]
    ML_INLINE float Sqrt01( float x )
    { return sqrt( saturate( x ) ); }

    ML_INLINE float2 Sqrt01( float2 x )
    { return sqrt( saturate( x ) ); }

    ML_INLINE float3 Sqrt01( float3 x )
    { return sqrt( saturate( x ) ); }

    ML_INLINE float4 Sqrt01( float4 x )
    { return sqrt( saturate( x ) ); }

    // 1 / Sqrt
    #define ML_POSITIVE_RSQRT_BUILTIN 0
    #define ML_POSITIVE_RSQRT_BUILTIN_SAFE 1
    #define ML_POSITIVE_RSQRT_ACCURATE 2
    #define ML_POSITIVE_RSQRT_ACCURATE_SAFE 3

    ML_INLINE float Rsqrt( float x, compiletime const uint mode = ML_RSQRT_DEFAULT )
    {
        if( mode <= ML_POSITIVE_RSQRT_BUILTIN_SAFE )
            return rsqrt( mode == ML_POSITIVE_RSQRT_BUILTIN ? x : max( x, ML_SMALL_EPS ) );

        return 1.0f / sqrt( mode == ML_POSITIVE_RSQRT_ACCURATE ? x : max( x, ML_SMALL_EPS ) );
    }

    ML_INLINE float2 Rsqrt( float2 x, compiletime const uint mode = ML_RSQRT_DEFAULT )
    {
        if( mode <= ML_POSITIVE_RSQRT_BUILTIN_SAFE )
            return rsqrt( mode == ML_POSITIVE_RSQRT_BUILTIN ? x : max( x, ML_SMALL_EPS ) );

        return 1.0f / sqrt( mode == ML_POSITIVE_RSQRT_ACCURATE ? x : max( x, ML_SMALL_EPS ) );
    }

    ML_INLINE float3 Rsqrt( float3 x, compiletime const uint mode = ML_RSQRT_DEFAULT )
    {
        if( mode <= ML_POSITIVE_RSQRT_BUILTIN_SAFE )
            return rsqrt( mode == ML_POSITIVE_RSQRT_BUILTIN ? x : max( x, ML_SMALL_EPS ) );

        return 1.0f / sqrt( mode == ML_POSITIVE_RSQRT_ACCURATE ? x : max( x, ML_SMALL_EPS ) );
    }

    ML_INLINE float4 Rsqrt( float4 x, compiletime const uint mode = ML_RSQRT_DEFAULT )
    {
        if( mode <= ML_POSITIVE_RSQRT_BUILTIN_SAFE )
            return rsqrt( mode == ML_POSITIVE_RSQRT_BUILTIN ? x : max( x, ML_SMALL_EPS ) );

        return 1.0f / sqrt( mode == ML_POSITIVE_RSQRT_ACCURATE ? x : max( x, ML_SMALL_EPS ) );
    }

    // Acos(x) (approximate)
    // https://www.desmos.com/calculator/x6ut8ros1u
    #define _AcosApprox( x ) ( sqrt( 2.0f ) * sqrt( saturate( 1.0f - x ) ) )

    ML_INLINE float AcosApprox( float x )
    { return _AcosApprox( x ); }

    ML_INLINE float2 AcosApprox( float2 x )
    { return _AcosApprox( x ); }

    ML_INLINE float3 AcosApprox( float3 x )
    { return _AcosApprox( x ); }

    ML_INLINE float4 AcosApprox( float4 x )
    { return _AcosApprox( x ); }

    // Atan(x) (approximate, for x in range [-1; 1])
    // https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1628884
    // https://www.desmos.com/calculator/0h8hv7kfp6
    #define _AtanApprox( x ) ( Math::Pi( 0.25f ) * x - ( abs( x ) * x - x ) * ( 0.2447f + 0.0663f * abs( x ) ) )

    ML_INLINE float AtanApprox( float x )
    { return _AtanApprox( x ); }

    ML_INLINE float2 AtanApprox( float2 x )
    { return _AtanApprox( x ); }

    ML_INLINE float3 AtanApprox( float3 x )
    { return _AtanApprox( x ); }

    ML_INLINE float4 AtanApprox( float4 x )
    { return _AtanApprox( x ); }

    // 1 / positive
    #define ML_POSITIVE_RCP_BUILTIN 0
    #define ML_POSITIVE_RCP_BUILTIN_SAFE 1
    #define ML_POSITIVE_RCP_ACCURATE 2
    #define ML_POSITIVE_RCP_ACCURATE_SAFE 3

    ML_INLINE float PositiveRcp( float x, compiletime const uint mode = ML_POSITIVE_RCP_DEFAULT )
    {
        if( mode <= ML_POSITIVE_RCP_BUILTIN_SAFE )
            return rcp( mode == ML_POSITIVE_RCP_BUILTIN ? x : max( x, ML_SMALL_EPS ) );

        return 1.0f / ( mode == ML_POSITIVE_RCP_ACCURATE ? x : max( x, ML_SMALL_EPS ) );
    }

    ML_INLINE float2 PositiveRcp( float2 x, compiletime const uint mode = ML_POSITIVE_RCP_DEFAULT )
    {
        if( mode <= ML_POSITIVE_RCP_BUILTIN_SAFE )
            return rcp( mode == ML_POSITIVE_RCP_BUILTIN ? x : max( x, ML_SMALL_EPS ) );

        return 1.0f / ( mode == ML_POSITIVE_RCP_ACCURATE ? x : max( x, ML_SMALL_EPS ) );
    }

    ML_INLINE float3 PositiveRcp( float3 x, compiletime const uint mode = ML_POSITIVE_RCP_DEFAULT )
    {
        if( mode <= ML_POSITIVE_RCP_BUILTIN_SAFE )
            return rcp( mode == ML_POSITIVE_RCP_BUILTIN ? x : max( x, ML_SMALL_EPS ) );

        return 1.0f / ( mode == ML_POSITIVE_RCP_ACCURATE ? x : max( x, ML_SMALL_EPS ) );
    }

    ML_INLINE float4 PositiveRcp( float4 x, compiletime const uint mode = ML_POSITIVE_RCP_DEFAULT )
    {
        if( mode <= ML_POSITIVE_RCP_BUILTIN_SAFE )
            return rcp( mode == ML_POSITIVE_RCP_BUILTIN ? x : max( x, ML_SMALL_EPS ) );

        return 1.0f / ( mode == ML_POSITIVE_RCP_ACCURATE ? x : max( x, ML_SMALL_EPS ) );
    }

    // LengthSquared
    ML_INLINE float LengthSquared( float2 v )
    { return dot( v, v ); }

    ML_INLINE float LengthSquared( float3 v )
    { return dot( v, v ); }

    ML_INLINE float LengthSquared( float4 v )
    { return dot( v, v ); }

    // Distance
    ML_INLINE float Distance( float2 a, float2 b )
    { return length( a - b ); }

    ML_INLINE float Distance( float3 a, float3 b )
    { return length( a - b ); }

    // Manhattan distance
    ML_INLINE float ManhattanDistance( float2 a, float2 b )
    { return dot( abs( a - b ), 1.0f ); }

    ML_INLINE float ManhattanDistance( float3 a, float3 b )
    { return dot( abs( a - b ), 1.0f ); }

    // Bit operations
    ML_INLINE uint ReverseBits4( uint x )
    {
        x = ( ( x & 0x5 ) << 1 ) | ( ( x & 0xA ) >> 1 );
        x = ( ( x & 0x3 ) << 2 ) | ( ( x & 0xC ) >> 2 );

        return x;
    }

    ML_INLINE uint ReverseBits8( uint x )
    {
        x = ( ( x & 0x55 ) << 1 ) | ( ( x & 0xAA ) >> 1 );
        x = ( ( x & 0x33 ) << 2 ) | ( ( x & 0xCC ) >> 2 );
        x = ( ( x & 0x0F ) << 4 ) | ( ( x & 0xF0 ) >> 4 );

        return x;
    }

    ML_INLINE uint ReverseBits16( uint x )
    {
        x = ( ( x & 0x5555 ) << 1 ) | ( ( x & 0xAAAA ) >> 1 );
        x = ( ( x & 0x3333 ) << 2 ) | ( ( x & 0xCCCC ) >> 2 );
        x = ( ( x & 0x0F0F ) << 4 ) | ( ( x & 0xF0F0 ) >> 4 );
        x = ( ( x & 0x00FF ) << 8 ) | ( ( x & 0xFF00 ) >> 8 );

        return x;
    }

    ML_INLINE uint ReverseBits32( uint x )
    {
    #ifndef __cplusplus
        x = reversebits( x );
    #else
        x = ( x << 16 ) | ( x >> 16 );
        x = ( ( x & 0x55555555 ) << 1 ) | ( ( x & 0xAAAAAAAA ) >> 1 );
        x = ( ( x & 0x33333333 ) << 2 ) | ( ( x & 0xCCCCCCCC ) >> 2 );
        x = ( ( x & 0x0F0F0F0F ) << 4 ) | ( ( x & 0xF0F0F0F0 ) >> 4 );
        x = ( ( x & 0x00FF00FF ) << 8 ) | ( ( x & 0xFF00FF00 ) >> 8 );
    #endif

        return x;
    }

    ML_INLINE uint CompactBits( uint x )
    {
        x &= 0x55555555;
        x = ( x ^ ( x >> 1 ) ) & 0x33333333;
        x = ( x ^ ( x >> 2 ) ) & 0x0F0F0F0F;
        x = ( x ^ ( x >> 4 ) ) & 0x00FF00FF;
        x = ( x ^ ( x >> 8 ) ) & 0x0000FFFF;

        return x;
    }
}

//=======================================================================================================================
// GEOMETRY
//=======================================================================================================================

namespace Geometry
{
    ML_INLINE float4 GetRotator( float angle )
    {
        float ca = cos( angle );
        float sa = sin( angle );

        return float4( ca, sa, -sa, ca );
    }

#ifndef __cplusplus
    ML_INLINE float3x3 GetRotator( float3 axis, float angle )
    {
        float sa = sin( angle );
        float ca = cos( angle );
        float one_ca = 1.0f - ca;

        float3 a = sa * axis;
        float3 b = one_ca * axis.xyx * axis.yzz;

        float3 t1 = one_ca * ( axis * axis ) + ca;
        float3 t2 = b.xyz - a.zxy;
        float3 t3 = b.zxy + a.yzx;

        return float3x3
        (
            t1.x, t2.x, t3.x,
            t3.y, t1.y, t2.y,
            t2.z, t3.z, t1.z
        );
    }
#endif

    ML_INLINE float4 GetRotator( float sa, float ca )
    { return float4( ca, sa, -sa, ca ); }

    ML_INLINE float4 CombineRotators( float4 r1, float4 r2 )
    { return float4( r1.xyxy ) * r2.xxzz + float4( r1.zwzw ) * r2.yyww; }

    ML_INLINE float4 ScaleRotator( float4 r, float scale )
    { return r * scale; }

    ML_INLINE float4 ScaleRotator( float4 r, float2 scale )
    { return float4( scale.x * r.xz, scale.y * r.yw ); }

    ML_INLINE float2 RotateVector( float4 rotator, float2 v )
    { return v.x * rotator.xz + v.y * rotator.yw; }

#ifndef __cplusplus
    ML_INLINE float3 RotateVector( float4x4 m, float3 v )
    { return mul( ( float3x3 )m, v ); }

    ML_INLINE float3 RotateVector( float3x3 m, float3 v )
    { return mul( m, v ); }
#endif

    ML_INLINE float2 RotateVectorInverse( float4 rotator, float2 v )
    { return v.x * rotator.xy + v.y * rotator.zw; }

#ifndef __cplusplus
    ML_INLINE float3 RotateVectorInverse( float4x4 m, float3 v )
    { return mul( ( float3x3 )transpose( m ), v ); }

    ML_INLINE float3 RotateVectorInverse( float3x3 m, float3 v )
    { return mul( transpose( m ), v ); }
#endif

    ML_INLINE float3 AffineTransform( float4x4 m, float3 p )
    { return mul( m, float4( p, 1.0f ) ).xyz; }

#ifndef __cplusplus
    ML_INLINE float3 AffineTransform( float3x4 m, float3 p )
    { return mul( m, float4( p, 1.0f ) ); }
#endif

    ML_INLINE float3 AffineTransform( float4x4 m, float4 p )
    { return mul( m, p ).xyz; }

    ML_INLINE float4 ProjectiveTransform( float4x4 m, float3 p )
    { return mul( m, float4( p, 1.0f ) ); }

    ML_INLINE float4 ProjectiveTransform( float4x4 m, float4 p )
    { return mul( m, p ); }

    ML_INLINE float2 GetPerpendicular( float2 v )
    { return float2( -v.y, v.x ); }

    ML_INLINE float3 GetPerpendicularVector( float3 N )
    {
        float3 T = float3( N.z, -N.x, N.y );
        T -= N * dot( T, N );

        return normalize( T );
    }

#ifndef __cplusplus
    // http://marc-b-reynolds.github.io/quaternions/2016/07/06/Orthonormal.html
    ML_INLINE float3x3 GetBasis( float3 N )
    {
        float sz = Math::Sign( N.z );
        float a  = 1.0f / ( sz + N.z );
        float ya = N.y * a;
        float b  = N.x * ya;
        float c  = N.x * sz;

        float3 T = float3( c * N.x * a - 1.0f, sz * b, c );
        float3 B = float3( b, N.y * ya - sz, N.y );

        // Note: due to the quaternion formulation, the generated frame is rotated by 180 degrees,
        // s.t. if N = (0, 0, 1), then T = (-1, 0, 0) and B = (0, -1, 0).
        return float3x3( T, B, N );
    }
#endif

    ML_INLINE float2 GetBarycentricCoords( float3 p, float3 a, float3 b, float3 c )
    {
        float3 v0 = b - a;
        float3 v1 = c - a;
        float3 v2 = p - a;

        float d00 = dot( v0, v0 );
        float d01 = dot( v0, v1 );
        float d11 = dot( v1, v1 );
        float d20 = dot( v2, v0 );
        float d21 = dot( v2, v1 );

        float2 barys;
        barys.x = d11 * d20 - d01 * d21;
        barys.y = d00 * d21 - d01 * d20;

        float invDenom = 1.0f / ( d00 * d11 - d01 * d01 );

        return barys * invDenom;
    }

    ML_INLINE float DistanceAttenuation( float dist, float Rmax )
    {
        // [Brian Karis 2013, "Real Shading in Unreal Engine 4 ( course notes )"]
        float falloff = dist / Rmax;
        falloff *= falloff;
        falloff = saturate( 1.0f - falloff * falloff );
        falloff *= falloff;

        float atten = falloff;
        atten *= Math::PositiveRcp( dist * dist + 1.0f );

        return atten;
    }

    ML_INLINE float3 UnpackLocalNormal( float2 localNormal, bool isUnorm = true )
    {
        float3 n;
        n.xy = isUnorm ? min( localNormal * ( 255.0f / 127.0f ) - 1.0f, 1.0f ) : localNormal;
        n.z = Math::Sqrt01( 1.0f - Math::LengthSquared( n.xy ) );

        return n;
    }

    ML_INLINE float3 TransformLocalNormal( float2 localNormal, float4 T, float3 N )
    {
        float3 n = UnpackLocalNormal( localNormal );
        float3 B = cross( N, T.xyz ); // TODO: potentially "normalize" is needed here

        return normalize( n.x * T.xyz + T.w * n.y * B + n.z * N );
    }

    ML_INLINE float SolidAngle( float cosHalfAngle )
    {
        return Math::Pi( 2.0f ) * ( 1.0f - cosHalfAngle );
    }

    // orthoMode = { 0 - perspective, -1 - right handed ortho, 1 - left handed ortho }
    ML_INLINE float3 ReconstructViewPosition( float2 uv, float4 cameraFrustum, float viewZ = 1.0, float orthoMode = 0.0f )
    {
        float3 p;
        p.xy = uv * cameraFrustum.zw + cameraFrustum.xy;
        p.xy *= viewZ * ( 1.0f - abs( orthoMode ) ) + orthoMode;
        p.z = viewZ;

        return p;
    }

    ML_INLINE float2 GetScreenUv( float4x4 worldToClip, float3 X, bool killBackprojection = false )
    {
        float4 clip = Geometry::ProjectiveTransform( worldToClip, X );

        #if( ML_WINDOW_ORIGIN_OGL == 1 )
            float2 uv = ( clip.xy / clip.w ) * 0.5f + 0.5f;
        #else
            float2 uv = ( float2( clip.xy ) / clip.w ) * float2( 0.5f, -0.5f ) + 0.5f;
        #endif

        if( killBackprojection )
            uv = clip.w < 0.0 ? 99999.0f : uv;

        return uv;
    }

    #define ML_SCREEN_MOTION 0
    #define ML_WORLD_MOTION 1

    ML_INLINE float2 GetPrevUvFromMotion( float2 uv, float3 X, float4x4 worldToClipPrev, float3 motionVector, compiletime const uint motionType = ML_WORLD_MOTION )
    {
        float3 Xprev = X + motionVector;
        float2 uvPrev = GetScreenUv( worldToClipPrev, Xprev );

        if( motionType == ML_SCREEN_MOTION )
            uvPrev = uv + motionVector.xy;

        return uvPrev;
    }

#ifndef __cplusplus
    ML_INLINE float3x3 GetMirrorMatrix( float3 n )
    {
        float3x3 m;
        m[ 0 ] = float3( 1.0f - 2.0f * n.x * n.x, 0.0f - 2.0f * n.y * n.x, 0.0f - 2.0f * n.z * n.x );
        m[ 1 ] = float3( 0.0f - 2.0f * n.x * n.y, 1.0f - 2.0f * n.y * n.y, 0.0f - 2.0f * n.z * n.y );
        m[ 2 ] = float3( 0.0f - 2.0f * n.x * n.z, 0.0f - 2.0f * n.y * n.z, 1.0f - 2.0f * n.z * n.z );

        return m;
    }
#endif
}

//=======================================================================================================================
// COLOR
//=======================================================================================================================

// https://chrisbrejon.com/cg-cinematography/chapter-1-color-management/
// https://viereck.ch/hue-xy-rgb/
// https://handwiki.org/wiki/Color_spaces_with_RGB_primaries

namespace Color
{
    ML_INLINE float Luminance( float3 x )
    {
        // https://en.wikipedia.org/wiki/Relative_luminance

        return dot( x, float3( 0.2126f, 0.7152f, 0.0722f ) );
    }

    ML_INLINE float3 Saturation( float3 x, float amount )
    {
        float luma = Luminance( x );

        return lerp( x, luma, amount );
    }

    /*
    Gamma ramps and encoding transfer functions
    Taken from https://github.com/Microsoft/DirectX-Graphics-Samples/blob/master/MiniEngine/Core/Shaders/ColorSpaceUtility.hlsli

    Orthogonal to color space though usually tightly coupled. For instance, sRGB is both a
    color space (defined by three basis vectors and a white point) and a gamma ramp. Gamma
    ramps are designed to reduce perceptual error when quantizing floats to integers with a
    limited number of bits. More variation is needed in darker colors because our eyes are
    more sensitive in the dark. The way the curve helps is that it spreads out dark values
    across more code words allowing for more variation. Likewise, bright values are merged
    together into fewer code words allowing for less variation.

    The sRGB curve is not a true gamma ramp but rather a piecewise function comprising a linear
    section and a power function. When sRGB-encoded colors are passed to an LCD monitor, they
    look correct on screen because the monitor expects the colors to be encoded with sRGB, and it
    removes the sRGB curve to linearize the values. When textures are encoded with sRGB, as many
    are, the sRGB curve needs to be removed before involving the colors in linear mathematics such
    as physically based lighting.
    */

    ML_INLINE float3 ToGamma( float3 x, float gamma = 2.2f )
    { return Math::Pow01( x, 1.0f / gamma ); }

    ML_INLINE float3 FromGamma( float3 x, float gamma = 2.2f )
    { return Math::Pow01( x, gamma ); }

    // "Full RGB": approximately pow( x, 1.0f / 2.2f )

    ML_INLINE float3 ToSrgb( float3 x )
    {
        const float4 consts = float4( 1.055f, 0.41666f, -0.055f, 12.92f );
        return lerp( x * consts.w, consts.x * Math::Pow( x, consts.yyy ) + consts.z, step( 0.0031308f, x ) );
    }

    ML_INLINE float3 FromSrgb( float3 x )
    {
        const float4 consts = float4( 1.0f / 12.92f, 1.0f / 1.055f, 0.055f / 1.055f, 1.0f / 0.41666f );
        return lerp( x * consts.x, Math::Pow( x * consts.y + consts.z, consts.www ), step( 0.04045f, x ) );
    }

    // "Limited RGB"
    // The OETF (opto-electronic transfer function) recommended for content shown on HDTVs.
    // This "gamma ramp" may increase contrast as appropriate for viewing in a dark environment.
    // Always use this curve with "Limited RGB" as it is used in conjunction with HDTVs.

    ML_INLINE float3 ToRec709( float3 x )
    {
        const float4 consts = float4( 1.0993f, 0.45f, -0.0993f, 4.5f );
        return lerp( x * consts.w, consts.x * Math::Pow( x, consts.yyy ) + consts.zzz, step( 0.0181f, x ) );
    }

    ML_INLINE float3 FromRec709( float3 x )
    {
        const float4 consts = float4( 1.0f / 4.5f, 1.0f / 1.0993f, 0.0993f / 1.0993f, 1.0f / 0.45f );
        return lerp( x * consts.x, Math::Pow( x * consts.y + consts.z, consts.www ), step( 0.08145f, x ) );
    }

    // This is the new HDR transfer function, also called "PQ" for perceptual quantizer. Note that REC2084
    // does not also refer to a color space. REC2084 is typically used with the REC2020 color space.

    ML_INLINE float3 ToRec2084( float3 x )
    {
        const float m1 = 2610.0f / 4096.0f / 4.0f;
        const float m2 = 2523.0f / 4096.0f * 128.0f;
        const float c1 = 3424.0f / 4096.0f;
        const float c2 = 2413.0f / 4096.0f * 32.0f;
        const float c3 = 2392.0f / 4096.0f * 32.0f;

        float3 Lp = pow( x, m1 );

        return pow( ( c1 + c2 * Lp ) / ( 1.0f + c3 * Lp ), m2 );
    }

    ML_INLINE float3 FromRec2084( float3 x )
    {
        const float m1 = 2610.0f / 4096.0f / 4.0f;
        const float m2 = 2523.0f / 4096.0f * 128.0f;
        const float c1 = 3424.0f / 4096.0f;
        const float c2 = 2413.0f / 4096.0f * 32.0f;
        const float c3 = 2392.0f / 4096.0f * 32.0f;

        float3 Np = pow( x, 1.0f / m2 );

        return pow( max( Np - c1, 0.0f ) / ( c2 - c3 * Np ), 1.0f / m1 );
    }

    /*
    Color space conversions:
    Taken from https://github.com/Microsoft/DirectX-Graphics-Samples/blob/master/MiniEngine/Core/Shaders/ColorSpaceUtility.hlsli

    These assume linear (not gamma-encoded) values. A color space conversion is a change
    of basis (like in Linear Algebra). Since a color space is defined by three vectors,
    the basis vectors, changing space involves a matrix-vector multiplication. Note that
    changing the color space may result in colors that are "out of bounds" because some
    color spaces have larger gamuts than others. When converting some colors from a wide
    gamut to small gamut, negative values may result, which are inexpressible in that new
    color space.

    It would be ideal to build a color pipeline which never throws away inexpressible (but
    perceivable) colors. This means using a color space that is as wide as possible. The
    XYZ color space is the neutral, all-encompassing color space, but it has the unfortunate
    property of having negative values (specifically in X and Z). To correct this, a further
    transformation can be made to X and Z to make them always positive. They can have their
    precision needs reduced by dividing by Y, allowing X and Z to be packed into two UNORM8s.
    This color space is called YUV for lack of a better name.

    Note: Rec.709 and sRGB share the same color primaries and white point. Their only difference
    is the transfer curve used.
    */

    // YCoCg

    ML_INLINE float3 RgbToYCoCg( float3 x )
    {
        float Y = dot( x, float3( 0.25, 0.5, 0.25 ) );
        float Co = dot( x, float3( 0.5, 0.0, -0.5 ) );
        float Cg = dot( x, float3( -0.25, 0.5, -0.25 ) );

        return float3( Y, Co, Cg );
    }

    ML_INLINE float3 YCoCgToRgb( float3 x )
    {
        float t = x.x - x.z;

        float3 r;
        r.y = x.x + x.z;
        r.x = t + x.y;
        r.z = t - x.y;

        return r;
    }

#ifndef __cplusplus
    // REC2020

    ML_INLINE float3 RgbToRec2020( float3 x )
    {
        static const float3x3 M =
        {
            0.627402, 0.329292, 0.043306,
            0.069095, 0.919544, 0.011360,
            0.016394, 0.088028, 0.895578
        };

        return mul( M, x );
    }

    ML_INLINE float3 Rec2020ToRgb( float3 x )
    {
        static const float3x3 M =
        {
            1.660496, -0.587656, -0.072840,
            -0.124547, 1.132895, -0.008348,
            -0.018154, -0.100597, 1.118751
        };

        return mul( M, x );
    }

        // DCIP3

    ML_INLINE float3 RgbToDcip3( float3 x )
    {
        static const float3x3 M =
        {
            0.822458, 0.177542, 0.000000,
            0.033193, 0.966807, 0.000000,
            0.017085, 0.072410, 0.910505
        };

        return mul( M, x );
    }

    ML_INLINE float3 Dcip3ToRgb( float3 x )
    {
        static const float3x3 M =
        {
            1.224947, -0.224947, 0.000000,
            -0.042056, 1.042056, 0.000000,
            -0.019641, -0.078651, 1.098291
        };

        return mul( M, x );
    }

    // CIE XYZ

    ML_INLINE float3 RgbToXyz( float3 x )
    {
        static const float3x3 M =
        {
            0.4123907992659595, 0.3575843393838780, 0.1804807884018343,
            0.2126390058715104, 0.7151686787677559, 0.0721923153607337,
            0.0193308187155918, 0.1191947797946259, 0.9505321522496608
        };

        return mul( M, x );
    }

    ML_INLINE float3 XyzToRgb( float3 x )
    {
        static const float3x3 M =
        {
            3.240969941904522, -1.537383177570094, -0.4986107602930032,
            -0.9692436362808803, 1.875967501507721, 0.04155505740717569,
            0.05563007969699373, -0.2039769588889765, 1.056971514242878
        };

        return mul( M, x );
    }

    // Encode an RGB color into a 32-bit LogLuv HDR format. The supported luminance range is roughly 10^-6..10^6 in 0.17% steps.
    // The log-luminance is encoded with 14 bits and chroma with 9 bits each. This was empirically more accurate than using 8 bit chroma.
    // Black (all zeros) is handled exactly
    ML_INLINE uint ToLogLuv( float3 x )
    {
        // Convert RGB to XYZ
        float3 XYZ = RgbToXyz( x );

        // Encode log2( Y ) over the range [ -20, 20 ) in 14 bits ( no sign bit ).
        // TODO: Fast path that uses the bits from the fp32 representation directly
        float logY = 409.6f * ( log2( XYZ.y ) + 20.0f ); // -inf if Y == 0
        uint Le = uint( clamp( logY, 0.0f, 16383.0f ) );

        // Early out if zero luminance to avoid NaN in chroma computation.
        // Note Le == 0 if Y < 9.55e-7. We'll decode that as exactly zero
        if( Le == 0 )
            return 0;

        // Compute chroma (u,v) values by:
        //  x = X / ( X + Y + Z )
        //  y = Y / ( X + Y + Z )
        //  u = 4x / ( -2x + 12y + 3 )
        //  v = 9y / ( -2x + 12y + 3 )
        // These expressions can be refactored to avoid a division by:
        //  u = 4X / ( -2X + 12Y + 3(X + Y + Z) )
        //  v = 9Y / ( -2X + 12Y + 3(X + Y + Z) )
        float invDenom = 1.0f / ( -2.0f * XYZ.x + 12.0f * XYZ.y + 3.0f * ( XYZ.x + XYZ.y + XYZ.z ) );
        float2 uv = float2( 4.0f, 9.0f ) * XYZ.xy * invDenom;

        // Encode chroma (u,v) in 9 bits each.
        // The gamut of perceivable uv values is roughly [0,0.62], so scale by 820 to get 9-bit values
        uint2 uve = uint2( clamp( 820.0f * uv, 0.0, 511.0f ) );

        return ( Le << 18 ) | ( uve.x << 9 ) | uve.y;
    }

    // Decode an RGB color stored in a 32-bit LogLuv HDR format
    ML_INLINE float3 FromLogLuv( uint x )
    {
        // Decode luminance Y from encoded log-luminance
        uint Le = x >> 18;
        if( Le == 0 )
            return 0;

        float logY = ( float( Le ) + 0.5f ) / 409.6f - 20.0f;
        float Y = exp2( logY );

        // Decode normalized chromaticity xy from encoded chroma (u,v)
        //  x = 9u / (6u - 16v + 12)
        //  y = 4v / (6u - 16v + 12)
        uint2 uve = uint2( x >> 9, x ) & 0x1ff;
        float2 uv = ( float2( uve ) + 0.5f ) / 820.0f;

        float invDenom = 1.0f / ( 6.0f * uv.x - 16.0f * uv.y + 12.0f );
        float2 xy = float2( 9.0f, 4.0f ) * uv * invDenom;

        // Convert chromaticity to XYZ and back to RGB.
        //  X = Y / y * x
        //  Z = Y / y * (1 - x - y)
        float s = Y / xy.y;
        float3 XYZ = float3( s * xy.x, Y, s * ( 1.0f - xy.x - xy.y ) );

        // Convert back to RGB and clamp to avoid out-of-gamut colors
        float3 color = max( XyzToRgb( XYZ ), 0.0f );

        return color;
    }
#endif

    // HDR compression ( tone mapping )
    ML_INLINE float3 HdrToLinear( float3 colorMulExposure )
    {
        float3 x0 = colorMulExposure * 0.38317f;
        float3 x1 = FromGamma( 1.0f - exp( -colorMulExposure ) );
        float3 color = lerp( x0, x1, step( 1.413f, colorMulExposure ) );

        return color;
    }

    ML_INLINE float3 HdrToLinear_Reinhard( float3 color, float exposure = 1.0f )
    {
        float luma = Luminance( color );

        return color * Math::PositiveRcp( 1.0f + luma * exposure );
    }

    ML_INLINE float3 _UnchartedCurve( float3 x )
    {
        float A = 0.22f; // Shoulder Strength
        float B = 0.3f;  // Linear Strength
        float C = 0.1f;  // Linear Angle
        float D = 0.2f;  // Toe Strength
        float E = 0.01f; // Toe Numerator
        float F = 0.3f;  // Toe Denominator

        return ( ( x * ( A * x + C * B ) + D * E ) / ( x * ( A * x + B ) + D * F ) ) - ( E / F );
    }

    ML_INLINE float3 HdrToLinear_Uncharted( float3 colorMulExposure, float whitePoint = 11.2f )
    {
        // John Hable's Uncharted 2 filmic tone mappping
        return _UnchartedCurve( colorMulExposure ) / _UnchartedCurve( whitePoint ).x;
    }

    ML_INLINE float3 HdrToLinear_Aces( float3 colorMulExposure )
    {
        // Cancel out the pre-exposure mentioned in https://knarkowicz.wordpress.com/2016/01/06/aces-filmic-tone-mapping-curve/
        colorMulExposure *= 0.6f;

        float A = 2.51f;
        float B = 0.03f;
        float C = 2.43f;
        float D = 0.59f;
        float E = 0.14f;

        return ( ( colorMulExposure * ( A * colorMulExposure + B ) ) * Math::PositiveRcp( colorMulExposure * ( C * colorMulExposure + D ) + E ) );
    }

    // HDR decompression
    ML_INLINE float3 LinearToHdr( float3 color )
    {
        float3 x0 = color / 0.38317f;
        float3 x1 = -log( max( 1.0f - ToGamma( color ), ML_EPS ) );
        float3 colorMulExposure = lerp( x0, x1, step( 1.413f, x0 ) );

        return colorMulExposure;
    }

    ML_INLINE float3 LinearToHdr_Reinhard( float3 color, float exposure = 1.0f )
    {
        float luma = Luminance( color );

        return color * Math::PositiveRcp( 1.0f - luma * exposure );
    }

    // Blending functions
    ML_INLINE float4 BlendSoft( float4 a, float4 b )
    {
        float4 t = 1.0f - 2.0f * b;
        float4 c = ( 2.0f * b + a * t ) * a;
        float4 d = 2.0f * a * ( 1.0f - b ) - Math::Sqrt( a ) * t;

        return lerp( c, d, step( 0.5f, b ) );
    }

    ML_INLINE float4 BlendDarken( float4 a, float4 b )
    { return lerp( a, b, step( b, a ) ); }

    ML_INLINE float4 BlendDifference( float4 a, float4 b )
    { return abs( a - b ); }

    ML_INLINE float4 BlendScreen( float4 a, float4 b )
    { return a + b * ( 1.0f - a ); }

    ML_INLINE float4 BlendOverlay( float4 a, float4 b )
    {
        float4 c = 2.0f * a * b;
        float4 d = 2.0f * BlendScreen( a, b ) - 1.0f;

        return lerp( c, d, step( 0.5f, a ) );
    }

    // Color clamping
    #define _Clamp( m1, sigma, input ) clamp( input, m1 - sigma, m1 + sigma )

    ML_INLINE float4 Clamp( float4 m1, float4 sigma, float4 color )
    { return _Clamp( m1, sigma, color ); }

    ML_INLINE float3 Clamp( float3 m1, float3 sigma, float3 color )
    { return _Clamp( m1, sigma, color ); }

    ML_INLINE float2 Clamp( float2 m1, float2 sigma, float2 color )
    { return _Clamp( m1, sigma, color ); }

    ML_INLINE float Clamp( float m1, float sigma, float color )
    { return _Clamp( m1, sigma, color ); }

    // More correct color clamping for RGB color space
    ML_INLINE float3 ClampAabb( float3 m1, float3 sigma, float3 color )
    {
        float3 center = m1;
        float3 extents = sigma;

        float3 d = color - center;
        float3 ts = abs( extents / ( d + 0.0001f ) );
        float t = min( ts.x, min( ts.y, ts.z ) );

        return center + d * saturate( t );
    }

    // Misc
    ML_INLINE float3 ColorizeLinear( float x )
    {
        x = saturate( x );

        float3 color;
        if( x < 0.25f )
            color = lerp( float3( 0, 0, 0 ), float3( 0, 0, 1 ), Math::SmoothStep( 0.00f, 0.25f, x ) );
        else if( x < 0.50f )
            color = lerp( float3( 0, 0, 1 ), float3( 0, 1, 0 ), Math::SmoothStep( 0.25f, 0.50f, x ) );
        else if( x < 0.75f )
            color = lerp( float3( 0, 1, 0 ), float3( 1, 1, 0 ), Math::SmoothStep( 0.50f, 0.75f, x ) );
        else
            color = lerp( float3( 1, 1, 0 ), float3( 1, 0, 0 ), Math::SmoothStep( 0.75f, 1.00f, x ) );

        return color;
    }

    // https://www.shadertoy.com/view/ls2Bz1
    ML_INLINE float3 ColorizeZucconi( float x )
    {
        // Original solution converts visible wavelengths of light (400-700 nm) (represented as x = [0; 1]) to RGB colors
        x = saturate( x ) * 0.85f;

        const float3 c1 = float3( 3.54585104f, 2.93225262f, 2.41593945f );
        const float3 x1 = float3( 0.69549072f, 0.49228336f, 0.27699880f );
        const float3 y1 = float3( 0.02312639f, 0.15225084f, 0.52607955f );

        float3 t = c1 * ( x - x1 );
        float3 a = saturate( 1.0f - t * t - y1 );

        const float3 c2 = float3( 3.90307140f, 3.21182957f, 3.96587128f );
        const float3 x2 = float3( 0.11748627f, 0.86755042f, 0.66077860f );
        const float3 y2 = float3( 0.84897130f, 0.88445281f, 0.73949448f );

        float3 k = c2 * ( x - x2 );
        float3 b = saturate( 1.0f - k * k - y2 );

        return saturate( a + b );
    }
}

//=======================================================================================================================
// PACKING
//=======================================================================================================================

namespace Packing
{
    // TODO: add signed packing / unpacking

    // Unsigned packing
    ML_INLINE uint RgbaToUint( float4 c, compiletime const uint Rbits, compiletime const uint Gbits = 0, compiletime const uint Bbits = 0, compiletime const uint Abits = 0 )
    {
        const uint Rmask = ( 1u << Rbits ) - 1u;
        const uint Gmask = ( 1u << Gbits ) - 1u;
        const uint Bmask = ( 1u << Bbits ) - 1u;
        const uint Amask = ( 1u << Abits ) - 1u;
        const uint Gshift = Rbits;
        const uint Bshift = Gshift + Gbits;
        const uint Ashift = Bshift + Bbits;
        const float4 scale = float4( float( Rmask ), float( Gmask ), float( Bmask ), float( Amask ) );

        uint4 p = uint4( saturate( c ) * scale + 0.5 );
        p.yzw <<= uint3( Gshift, Bshift, Ashift );
        p.xy |= p.zw;

        return p.x | p.y;
    }

    // Unsigned unpacking
    ML_INLINE float4 UintToRgba( uint p, compiletime const uint Rbits, compiletime const uint Gbits = 0, compiletime const uint Bbits = 0, compiletime const uint Abits = 0 )
    {
        const uint Rmask = ( 1u << Rbits ) - 1u;
        const uint Gmask = ( 1u << Gbits ) - 1u;
        const uint Bmask = ( 1u << Bbits ) - 1u;
        const uint Amask = ( 1u << Abits ) - 1u;
        const uint Gshift = Rbits;
        const uint Bshift = Gshift + Gbits;
        const uint Ashift = Bshift + Bbits;
        const float4 scale = 1.0f / max( float4( float( Rmask ), float( Gmask ), float( Bmask ), float( Amask ) ), 1.0f );

        uint4 c = p >> uint4( 0, Gshift, Bshift, Ashift );
        c &= uint4( Rmask, Gmask, Bmask, Amask );

        return float4( c ) * scale;
    }

    // Half float
    ML_INLINE uint Rg16fToUint( float2 c )
    {
        return ( f32tof16( c.y ) << 16 ) | ( f32tof16( c.x ) & 0xFFFF ); // TODO: 0xFFFF is a WAR for NV VK compiler bug (<= 461.xx)
    }

    ML_INLINE float2 UintToRg16f( uint p )
    {
        float2 c;
        c.x = f16tof32( p );
        c.y = f16tof32( p >> 16 );

        return c;
    }

    // RGBE - shared exponent, positive values only (Ward 1984)
    ML_INLINE uint EncodeRgbe( float3 c )
    {
        float sharedExp = ceil( log2( max( max( c.x, c.y ), c.z ) ) );
        float4 p = float4( c * exp2( -sharedExp ), ( sharedExp + 128.0f ) / 255.0f );

        return RgbaToUint( p, 8, 8, 8, 8 );
    }

    ML_INLINE float3 DecodeRgbe( uint p )
    {
        float4 c = UintToRgba( p, 8, 8, 8, 8 );

        return exp2( c.w * 255.0f - 128.0f ) * c.xyz;
    }

    // Octahedron packing for unit vectors
    // https://knarkowicz.wordpress.com/2014/04/16/octahedron-normal-vector-encoding/
    // [Cigolle 2014, "A Survey of Efficient Representations for Independent Unit Vectors"]
    // Error ( deg )
    //                    Mean      Max
    // oct     8:8        0.31485   0.63575
    // snorm   8:8:8      0.17015   0.38588
    // oct     10:10      0.07829   0.15722
    // snorm   10:10:10   0.04228   0.09598
    // oct     12:12      0.01953   0.03928
    // oct     16:16      0.00122   0.00246
    // snorm   16:16:16   0.00066   0.00149
    ML_INLINE float2 EncodeUnitVector( float3 v, compiletime const bool bSigned = false )
    {
        v /= dot( abs( v ), 1.0f );

        float2 octWrap = ( 1.0f - abs( v.yx ) ) * Math::Sign( v.xy );
        v.xy = v.z >= 0.0f ? v.xy : octWrap;

        return bSigned ? v.xy : 0.5f * v.xy + 0.5f;
    }

    ML_INLINE float3 DecodeUnitVector( float2 p, compiletime const bool bSigned = false, compiletime const bool bNormalize = true )
    {
        p = bSigned ? p : ( p * 2.0 - 1.0f );

        // https://twitter.com/Stubbesaurus/status/937994790553227264
        float3 n = float3( p.xy, 1.0f - abs( p.x ) - abs( p.y ) );
        float t = saturate( -n.z );
        n.xy -= t * Math::Sign( n.xy );

        return bNormalize ? normalize( n ) : n;
    }
}

//=======================================================================================================================
// FILTERING
//=======================================================================================================================

namespace Filtering
{
    ML_INLINE float GetModifiedRoughnessFromNormalVariance( float linearRoughness, float3 nonNormalizedAverageNormal )
    {
        // https://blog.selfshadow.com/publications/s2013-shading-course/rad/s2013_pbs_rad_notes.pdf (page 20)
        float l = length( nonNormalizedAverageNormal );
        float kappa = saturate( 1.0f - l * l ) * Math::PositiveRcp( l * ( 3.0f - l * l ) );

        return Math::Sqrt01( linearRoughness * linearRoughness + kappa );
    }

    // Mipmap level
    ML_INLINE float GetMipmapLevel( float duvdxMulTexSizeSq, float duvdyMulTexSizeSq, compiletime const float maxAnisotropy = 1.0f )
    {
        // duvdtMulTexSizeSq = ||dUV/dt * TexSize|| ^ 2

        float Pmax = max( duvdxMulTexSizeSq, duvdyMulTexSizeSq );

        if( maxAnisotropy > 1.0f )
        {
            float Pmin = min( duvdxMulTexSizeSq, duvdyMulTexSizeSq );
            float N = min( Pmax * Math::PositiveRcp( Pmin ), maxAnisotropy );
            Pmax *= Math::PositiveRcp( N );
        }

        float mip = 0.5f * log2( Pmax );

        return mip; // Yes, no clamping to 0 here!
    }

    // Nearest filter (for nearest sampling)
    struct Nearest
    {
        float2 origin;
    };

    ML_INLINE Nearest GetNearestFilter( float2 uv, float2 texSize )
    {
        float2 t = uv * texSize;

        Nearest result;
        result.origin = floor( t );

        return result;
    }

    // Bilinear filter (for nearest sampling)
    struct Bilinear
    {
        float2 origin;
        float2 weights;
    };

    ML_INLINE Bilinear GetBilinearFilter( float2 uv, float2 texSize )
    {
        float2 t = uv * texSize - 0.5;

        Bilinear result;
        result.origin = floor( t );
        result.weights = saturate( t - result.origin );

        return result;
    }

    ML_INLINE float ApplyBilinearFilter( float s00, float s10, float s01, float s11, Bilinear f )
    { return lerp( lerp( s00, s10, f.weights.x ), lerp( s01, s11, f.weights.x ), f.weights.y ); }

    ML_INLINE float2 ApplyBilinearFilter( float2 s00, float2 s10, float2 s01, float2 s11, Bilinear f )
    { return lerp( lerp( s00, s10, f.weights.x ), lerp( s01, s11, f.weights.x ), f.weights.y ); }

    ML_INLINE float3 ApplyBilinearFilter( float3 s00, float3 s10, float3 s01, float3 s11, Bilinear f )
    { return lerp( lerp( s00, s10, f.weights.x ), lerp( s01, s11, f.weights.x ), f.weights.y ); }

    ML_INLINE float4 ApplyBilinearFilter( float4 s00, float4 s10, float4 s01, float4 s11, Bilinear f )
    { return lerp( lerp( s00, s10, f.weights.x ), lerp( s01, s11, f.weights.x ), f.weights.y ); }

    ML_INLINE float4 GetBilinearCustomWeights( Bilinear f, float4 customWeights )
    {
        float2 oneMinusWeights = saturate( 1.0f - f.weights );

        float4 weights = customWeights;
        weights.x *= oneMinusWeights.x * oneMinusWeights.y;
        weights.y *= f.weights.x * oneMinusWeights.y;
        weights.z *= oneMinusWeights.x * f.weights.y;
        weights.w *= f.weights.x * f.weights.y;

        return weights;
    }

    // Normalization avoids dividing by small numbers to mitigate potential imprecision problems
    #define _ApplyBilinearCustomWeights( s00, s10, s01, s11, w, normalize ) \
        ( ( s00 * w.x + s10 * w.y + s01 * w.z + s11 * w.w ) * ( normalize ? ( dot( w, 1.0f ) < 0.0001f ? 0.0f : rcp( dot( w, 1.0f ) ) ) : 1.0f ) )

    ML_INLINE float ApplyBilinearCustomWeights( float s00, float s10, float s01, float s11, float4 w, compiletime const bool normalize = true )
    { return _ApplyBilinearCustomWeights( s00, s10, s01, s11, w, normalize ); }

    ML_INLINE float2 ApplyBilinearCustomWeights( float2 s00, float2 s10, float2 s01, float2 s11, float4 w, compiletime const bool normalize = true )
    { return _ApplyBilinearCustomWeights( s00, s10, s01, s11, w, normalize ); }

    ML_INLINE float3 ApplyBilinearCustomWeights( float3 s00, float3 s10, float3 s01, float3 s11, float4 w, compiletime const bool normalize = true )
    { return _ApplyBilinearCustomWeights( s00, s10, s01, s11, w, normalize ); }

    ML_INLINE float4 ApplyBilinearCustomWeights( float4 s00, float4 s10, float4 s01, float4 s11, float4 w, compiletime const bool normalize = true )
    { return _ApplyBilinearCustomWeights( s00, s10, s01, s11, w, normalize ); }

    // Catmull-Rom (for nearest sampling)
    struct CatmullRom
    {
        float2 origin;
        float2 weights[4];
    };

    ML_INLINE CatmullRom GetCatmullRomFilter( float2 uv, float2 texSize, float sharpness = 0.5 )
    {
        float2 tci = uv * texSize;
        float2 tc = floor( tci - 0.5f ) + 0.5f;
        float2 f = saturate( tci - tc );
        float2 f2 = f * f;
        float2 f3 = f2 * f;

        CatmullRom result;
        result.origin = tc - 1.5f;
        result.weights[ 0 ] = -sharpness * f3 + 2.0f * sharpness * f2 - sharpness * f;
        result.weights[ 1 ] = ( 2.0f - sharpness ) * f3 - ( 3.0f - sharpness ) * f2 + 1.0f;
        result.weights[ 2 ] = -( 2.0f - sharpness ) * f3 + ( 3.0f - 2.0f * sharpness ) * f2 + sharpness * f;
        result.weights[ 3 ] = sharpness * f3 - sharpness * f2;

        return result;
    }

    ML_INLINE float4 ApplyCatmullRomFilterNoCorners( CatmullRom filter, float4 s10, float4 s20, float4 s01, float4 s11, float4 s21, float4 s31, float4 s02, float4 s12, float4 s22, float4 s32, float4 s13, float4 s23 )
    {
        /*
        s00, s30, s03, s33 - are not used

              s10   s20
        s01   s11   s21   s31
        s02   s12   s22   s32
              s13   s23
        */

        float w = filter.weights[ 1 ].x * filter.weights[ 0 ].y;
        float4 color = s10 * w;
        float sum = w;

        w = filter.weights[ 2 ].x * filter.weights[ 0 ].y;
        color += s20 * w;
        sum += w;


        w = filter.weights[ 0 ].x * filter.weights[ 1 ].y;
        color += s01 * w;
        sum += w;

        w = filter.weights[ 1 ].x * filter.weights[ 1 ].y;
        color += s11 * w;
        sum += w;

        w = filter.weights[ 2 ].x * filter.weights[ 1 ].y;
        color += s21 * w;
        sum += w;

        w = filter.weights[ 3 ].x * filter.weights[ 1 ].y;
        color += s31 * w;
        sum += w;


        w = filter.weights[ 0 ].x * filter.weights[ 2 ].y;
        color += s02 * w;
        sum += w;

        w = filter.weights[ 1 ].x * filter.weights[ 2 ].y;
        color += s12 * w;
        sum += w;

        w = filter.weights[ 2 ].x * filter.weights[ 2 ].y;
        color += s22 * w;
        sum += w;

        w = filter.weights[ 3 ].x * filter.weights[ 2 ].y;
        color += s32 * w;
        sum += w;


        w = filter.weights[ 1 ].x * filter.weights[ 3 ].y;
        color += s13 * w;
        sum += w;

        w = filter.weights[ 2 ].x * filter.weights[ 3 ].y;
        color += s23 * w;
        sum += w;

        return color * Math::PositiveRcp( sum );
    }

    ML_INLINE float ApplyCatmullRomFilterNoCorners( CatmullRom filter, float s10, float s20, float s01, float s11, float s21, float s31, float s02, float s12, float s22, float s32, float s13, float s23 )
    {
        /*
        s00, s30, s03, s33 - are not used

              s10   s20
        s01   s11   s21   s31
        s02   s12   s22   s32
              s13   s23
        */

        float w = filter.weights[ 1 ].x * filter.weights[ 0 ].y;
        float color = s10 * w;
        float sum = w;

        w = filter.weights[ 2 ].x * filter.weights[ 0 ].y;
        color += s20 * w;
        sum += w;


        w = filter.weights[ 0 ].x * filter.weights[ 1 ].y;
        color += s01 * w;
        sum += w;

        w = filter.weights[ 1 ].x * filter.weights[ 1 ].y;
        color += s11 * w;
        sum += w;

        w = filter.weights[ 2 ].x * filter.weights[ 1 ].y;
        color += s21 * w;
        sum += w;

        w = filter.weights[ 3 ].x * filter.weights[ 1 ].y;
        color += s31 * w;
        sum += w;


        w = filter.weights[ 0 ].x * filter.weights[ 2 ].y;
        color += s02 * w;
        sum += w;

        w = filter.weights[ 1 ].x * filter.weights[ 2 ].y;
        color += s12 * w;
        sum += w;

        w = filter.weights[ 2 ].x * filter.weights[ 2 ].y;
        color += s22 * w;
        sum += w;

        w = filter.weights[ 3 ].x * filter.weights[ 2 ].y;
        color += s32 * w;
        sum += w;


        w = filter.weights[ 1 ].x * filter.weights[ 3 ].y;
        color += s13 * w;
        sum += w;

        w = filter.weights[ 2 ].x * filter.weights[ 3 ].y;
        color += s23 * w;
        sum += w;

        return color * Math::PositiveRcp( sum );
    }

    // Blur 1D
    // offsets = { -offsets.xy, offsets.zw, 0, offsets.xy, offsets.zw };
    ML_INLINE float4 GetBlurOffsets1D( float2 directionDivTexSize )
    { return float4( 1.7229f, 1.7229f, 3.8697f, 3.8697f ) * float4( directionDivTexSize.xy, directionDivTexSize.xy ); }

    // Blur 2D
    // offsets = { 0, offsets.xy, offsets.zw, offsets.wx, offsets.yz };
    ML_INLINE float4 GetBlurOffsets2D( float2 invTexSize )
    { return float4( 0.4f, 0.9f, -0.4f, -0.9f ) * float4( invTexSize.xy, invTexSize.xy ); }
}

//=======================================================================================================================
// SEQUENCE
//=======================================================================================================================

namespace Sequence
{
    // https://en.wikipedia.org/wiki/Ordered_dithering
    #define ML_BAYER_LINEAR 0
    #define ML_BAYER_REVERSEBITS 1

    // RESULT: [0; 15]
    ML_INLINE uint Bayer4x4ui( uint2 samplePos, uint frameIndex, compiletime const uint mode = ML_BAYER_DEFAULT )
    {
        uint2 samplePosWrap = samplePos & 3;
        uint a = 2068378560 * ( 1 - ( samplePosWrap.x >> 1 ) ) + 1500172770 * ( samplePosWrap.x >> 1 );
        uint b = ( samplePosWrap.y + ( ( samplePosWrap.x & 1 ) << 2 ) ) << 2;

        uint sampleOffset = mode == ML_BAYER_REVERSEBITS ? Math::ReverseBits4( frameIndex ) : frameIndex;

        return ( ( a >> b ) + sampleOffset ) & 0xF;
    }

    // RESULT: [0; 1)
    ML_INLINE float Bayer4x4( uint2 samplePos, uint frameIndex, compiletime const uint mode = ML_BAYER_DEFAULT )
    {
        uint bayer = Bayer4x4ui( samplePos, frameIndex, mode );

        return float( bayer ) / 16.0f;
    }

    // https://en.wikipedia.org/wiki/Low-discrepancy_sequence
    // RESULT: [0; 1)
    ML_INLINE float2 Hammersley2D( uint index, float sampleCount )
    {
        float x = float( index ) / sampleCount;
        float y = float( Math::ReverseBits32( index ) ) * 2.3283064365386963e-10f;

        return float2( x, y );
    }

    // https://en.wikipedia.org/wiki/Z-order_curve
    ML_INLINE uint2 Morton2D( uint index )
    {
        return uint2( Math::CompactBits( index ), Math::CompactBits( index >> 1 ) );
    }

    // Checkerboard pattern
    ML_INLINE uint CheckerBoard( uint2 samplePos, uint frameIndex )
    {
        uint a = samplePos.x ^ samplePos.y;

        return ( a ^ frameIndex ) & 0x1;
    }

    ML_INLINE uint IntegerExplode( uint x )
    {
        x = ( x | ( x << 8 ) ) & 0x00FF00FF;
        x = ( x | ( x << 4 ) ) & 0x0F0F0F0F;
        x = ( x | ( x << 2 ) ) & 0x33333333;
        x = ( x | ( x << 1 ) ) & 0x55555555;

        return x;
    }

    ML_INLINE uint Zorder( uint2 xy )
    { return IntegerExplode( xy.x ) | ( IntegerExplode( xy.y ) << 1 ); }

    ML_INLINE uint Lcg( uint x )
    {
        // http://en.wikipedia.org/wiki/Linear_congruential_generator
        return 1664525u * x + 1013904223u;
    }

    ML_INLINE uint XorShift( uint x )
    {
        // Xorshift algorithm from George Marsaglia's paper
        x ^= x << 13;
        x ^= x >> 17;
        x ^= x << 5;

        return x;
    }

    // NOTE: Hash( 0 ) = 0! If that's a problem do "Hash32( x + constant )". HashCombine does something similar already
    ML_INLINE uint Hash( uint x )
    {
        // This little gem is from https://nullprogram.com/blog/2018/07/31/, "Prospecting for Hash Functions" by Chris Wellons
        #if 1 // faster, higher bias
            x ^= x >> 16;
            x *= 0x7FEB352D;
            x ^= x >> 15;
            x *= 0x846CA68B;
            x ^= x >> 16;
        #else // slower, lower bias
            x ^= x >> 17;
            x *= 0xED5AD4BB;
            x ^= x >> 11;
            x *= 0xAC4C1B51;
            x ^= x >> 15;
            x *= 0x31848BAB;
            x ^= x >> 14;
        #endif

        return x;
    }

    ML_INLINE uint HashCombine( uint seed, uint value )
    { return seed ^ ( Hash( value ) + 0x9E3779B9 + ( seed << 6 ) + ( seed >> 2 ) ); }

    ML_INLINE float RadicalInverse( uint index, uint base )
    {
        float val = 0.0f;
        float rcpBase = 1.0f / ( float )base;
        float rcpBi = rcpBase;

        while( index > 0 )
        {
            uint m = index % base;
            val += float( m ) * rcpBi;
            index = uint( index * rcpBase );
            rcpBi *= rcpBase;
        }

        return val;
    }

    ML_INLINE float2 Halton2D( uint index )
    { return float2( RadicalInverse( index + 1, 3 ), Math::ReverseBits32( index + 1 ) * 2.3283064365386963e-10f ); }

    // https://extremelearning.com.au/unreasonable-effectiveness-of-quasirandom-sequences/
    ML_INLINE float Weyl1D( float p, int n )
    { return frac( p + float( n * 10368889 ) / exp2( 24.0f ) ); }

    ML_INLINE float2 Weyl2D( float2 p, int n )
    { return frac( p + float2( float( n * 12664745 ), float( n * 9560333 ) ) / exp2( 24.0f ) ); }

    ML_INLINE float3 Weyl3D( float3 p, int n )
    { return frac( p + float3( float( n * 13743434 ), float( n * 11258243 ), float( n * 9222443 ) ) / exp2( 24.0f ) ); }
}

//=======================================================================================================================
// RNG
//=======================================================================================================================

namespace Rng
{
    #define ML_RNG_LCG 0
    #define ML_RNG_XORSHIFT 1
    #define ML_RNG_HASH 2

    ML_INLINE uint _Next( uint seed )
    {
        #if( ML_RNG_NEXT_MODE == ML_RNG_LCG )
            seed = Sequence::Lcg( seed );
        #elif( ML_RNG_NEXT_MODE == ML_RNG_XORSHIFT )
            seed = Sequence::XorShift( seed );
        #else
            seed = Sequence::Hash( seed );
        #endif

        return seed;
    }

    #define ML_RNG_UTOF 0
    #define ML_RNG_MANTISSA_BITS 1

    #if( ML_RNG_FLOAT01_MODE == ML_RNG_UTOF )
        #define _UintToFloat01( x ) ( ( x >> 8 ) * ( 1.0f / float( 1 << 24 ) ) )
    #else
        #define _UintToFloat01( x ) ( 2.0f - asfloat( ( x >> 9 ) | 0x3F800000 ) )
    #endif

    // Tiny Encryption Algorithm
    namespace Tea
    {
#ifndef __cplusplus
        static uint2 rngTeaState;

        #define RNG_TEA_ARG
        #define RNG_TEA_INPUT
        #define RNG_TEA_ARG_COMMA
        #define RNG_TEA_INPUT_COMMA
#else
        #define RNG_TEA_ARG rngTeaState
        #define RNG_TEA_INPUT uint2& rngTeaState
        #define RNG_TEA_ARG_COMMA RNG_TEA_ARG,
        #define RNG_TEA_INPUT_COMMA RNG_TEA_INPUT,
#endif

        ML_INLINE void Initialize( RNG_TEA_INPUT_COMMA uint linearIndex, uint frameIndex, uint spinNum = 16 )
        {
            rngTeaState.x = linearIndex;
            rngTeaState.y = frameIndex;

            uint s = 0;
            for( uint n = 0; n < spinNum; n++ )
            {
                s += 0x9E3779B9;
                rngTeaState.x += ( ( rngTeaState.y << 4 ) + 0xA341316C ) ^ ( rngTeaState.y + s ) ^ ( ( rngTeaState.y >> 5 ) + 0xC8013EA4 );
                rngTeaState.y += ( ( rngTeaState.x << 4 ) + 0xAD90777D ) ^ ( rngTeaState.x + s ) ^ ( ( rngTeaState.x >> 5 ) + 0x7E95761E );
            }
        }

        ML_INLINE void Initialize( RNG_TEA_INPUT_COMMA uint2 samplePos, uint frameIndex, uint spinNum = 16 )
        { Initialize( RNG_TEA_ARG_COMMA Sequence::Zorder( samplePos ), frameIndex, spinNum ); }

        ML_INLINE uint GetUint( RNG_TEA_INPUT )
        {
            rngTeaState.x = _Next( rngTeaState.x );

            return rngTeaState.x;
        }

        ML_INLINE uint2 GetUint2( RNG_TEA_INPUT )
        {
            rngTeaState.x = _Next( rngTeaState.x );
            rngTeaState.y = _Next( rngTeaState.y );

            return rngTeaState;
        }

        ML_INLINE uint4 GetUint4( RNG_TEA_INPUT )
        { return uint4( GetUint2( RNG_TEA_ARG ), GetUint2( RNG_TEA_ARG ) ); }

        ML_INLINE float GetFloat( RNG_TEA_INPUT )
        { uint x = GetUint( RNG_TEA_ARG ); return _UintToFloat01( x ); }

        ML_INLINE float2 GetFloat2( RNG_TEA_INPUT )
        { uint2 x = GetUint2( RNG_TEA_ARG ); return _UintToFloat01( x ); }

        ML_INLINE float4 GetFloat4( RNG_TEA_INPUT )
        { uint4 x = GetUint4( RNG_TEA_ARG ); return _UintToFloat01( x ); }
    }

    // Hash-based
    namespace Hash
    {
#ifndef __cplusplus
        static uint rngHashState;

        #define RNG_HASH_ARG
        #define RNG_HASH_INPUT
        #define RNG_HASH_ARG_COMMA
        #define RNG_HASH_INPUT_COMMA
#else
        #define RNG_HASH_ARG rngHashState
        #define RNG_HASH_INPUT uint& rngHashState
        #define RNG_HASH_ARG_COMMA RNG_HASH_ARG,
        #define RNG_HASH_INPUT_COMMA RNG_HASH_INPUT,
#endif

        ML_INLINE void Initialize( RNG_HASH_INPUT_COMMA uint linearIndex, uint frameIndex )
        { rngHashState = Sequence::HashCombine( Sequence::Hash( frameIndex + 0x035F9F29 ), linearIndex ); }

        ML_INLINE void Initialize( RNG_HASH_INPUT_COMMA uint2 samplePos, uint frameIndex )
        { Initialize( RNG_HASH_ARG_COMMA Sequence::Zorder( samplePos ), frameIndex ); }

        ML_INLINE uint GetUint( RNG_HASH_INPUT )
        {
            rngHashState = _Next( rngHashState );

            return rngHashState;
        }

        ML_INLINE uint2 GetUint2( RNG_HASH_INPUT )
        { return uint2( GetUint( RNG_HASH_ARG ), GetUint( RNG_HASH_ARG ) ); }

        ML_INLINE uint4 GetUint4( RNG_HASH_INPUT )
        { return uint4( GetUint2( RNG_HASH_ARG ), GetUint2( RNG_HASH_ARG ) ); }

        ML_INLINE float GetFloat( RNG_HASH_INPUT )
        { uint x = GetUint( RNG_HASH_ARG ); return _UintToFloat01( x ); }

        ML_INLINE float2 GetFloat2( RNG_HASH_INPUT )
        { uint2 x = GetUint2( RNG_HASH_ARG ); return _UintToFloat01( x ); }

        ML_INLINE float4 GetFloat4( RNG_HASH_INPUT )
        { uint4 x = GetUint4( RNG_HASH_ARG ); return _UintToFloat01( x ); }
    }
}

//=======================================================================================================================
// BRDF
//=======================================================================================================================

/*
LINKS:
https://www.pbr-book.org/3ed-2018/contents
https://google.github.io/filament/Filament.html#materialsystem/specularbrdf
https://knarkowicz.wordpress.com/2014/12/27/analytical-dfg-term-for-ibl/
https://blog.selfshadow.com/publications/
*/

// "roughness" ( aka "alpha", aka "m" ) = specular or real roughness
// "linearRoughness" ( aka "perceptual roughness", aka "artistic roughness" ) = sqrt( roughness )
// G1 = G1( V, m ) is % visible in one direction
// G2 = G2( L, V, m ) is % visible in two directions ( in practice, derived from G1 )
// G2( uncorellated ) = G1( L, m ) * G1( V, m )
// Specular BRDF = F * D * G2 / ( 4.0 * NoV * NoL )

namespace BRDF
{
    //======================================================================================================================
    // Constants
    //======================================================================================================================

    namespace IOR
    {
        static const float Vacuum      = 1.0f;
        static const float Air         = 1.00029f; // at sea level
        static const float Ice         = 1.31f;
        static const float Water       = 1.333f;
        static const float Quartz      = 1.46f;
        static const float Glass       = 1.55f;
        static const float Sapphire    = 1.77f;
        static const float Diamond     = 2.42f;
    };

    //======================================================================================================================
    // Misc
    //======================================================================================================================

    ML_INLINE float Pow5( float x )
    { return Math::Pow01( 1.0f - x, 5.0f ); }

    ML_INLINE void ConvertBaseColorMetalnessToAlbedoRf0( float3 baseColor, float metalness, ML_OUT(float3) albedo, ML_OUT(float3) Rf0 )
    {
        // TODO: ideally, ML_RF0_DIELECTRICS needs to be replaced with reflectance "ML_RF0_DIELECTRICS = 0.16 * reflectance * reflectance"
        // see https://google.github.io/filament/Filament.html#toc4.8
        // see https://seblagarde.files.wordpress.com/2015/07/course_notes_moving_frostbite_to_pbr_v32.pdf (page 13)
        albedo = baseColor * saturate( 1.0f - metalness );
        Rf0 = lerp( ML_RF0_DIELECTRICS, baseColor, metalness );
    }

    ML_INLINE float FresnelTerm_Shadowing( float3 Rf0 )
    {
        // UE4: anything less than 2% is physically impossible and is instead considered to be shadowing
        return saturate( Color::Luminance( Rf0 ) / 0.02f );
    }

    //======================================================================================================================
    // Diffuse terms
    //======================================================================================================================

    ML_INLINE float DiffuseTerm_Lambert( float linearRoughness, float NoL, float NoV, float VoH )
    {
        ML_Unused( linearRoughness );
        ML_Unused( NoL );
        ML_Unused( NoV );
        ML_Unused( VoH );

        float d = 1.0f;

        return d / Math::Pi( 1.0f );
    }

    // [Burley 2012, "Physically-Based Shading at Disney"]
    ML_INLINE float DiffuseTerm_Burley( float linearRoughness, float NoL, float NoV, float VoH )
    {
        linearRoughness = saturate( linearRoughness );

        float energyBias = 0.5f;
        float energyFactor = 1.0f;

        float f = 2.0f * VoH * VoH * linearRoughness + energyBias - 1.0f; // yes, linear roughness
        float FdV = 1.0f + f * Pow5( NoV );
        float FdL = 1.0f + f * Pow5( NoL );
        float d = FdV * FdL * energyFactor;

        return d / Math::Pi( 1.0f );
    }

    // [Lagarde 2014, "Moving Frostbite to Physically Based Rendering 3.0"]
    // https://seblagarde.files.wordpress.com/2015/07/course_notes_moving_frostbite_to_pbr_v32.pdf (page 10)
    ML_INLINE float DiffuseTerm_BurleyFrostbite( float linearRoughness, float NoL, float NoV, float VoH )
    {
        linearRoughness = saturate( linearRoughness );

        float energyBias = lerp( 0.0f, 0.5f, linearRoughness );
        float energyFactor = lerp( 1.0f, 1.0f / 1.51f, linearRoughness );

        float f = 2.0f * VoH * VoH * linearRoughness + energyBias - 1.0f; // yes, linear roughness
        float FdV = 1.0f + f * Pow5( NoV );
        float FdL = 1.0f + f * Pow5( NoL );
        float d = FdV * FdL * energyFactor;

        return d / Math::Pi( 1.0f );
    }

    // [Gotanda 2012, "Beyond a Simple Physically Based Blinn-Phong Model in Real-Time"]
    ML_INLINE float DiffuseTerm_OrenNayar( float linearRoughness, float NoL, float NoV, float VoH )
    {
        float m = saturate( linearRoughness * linearRoughness );
        float m2 = m * m;
        float VoL = 2.0f * VoH - 1.0f;
        float c1 = 1.0f - 0.5f * m2 / ( m2 + 0.33f );
        float cosri = VoL - NoV * NoL;
        float a = cosri >= 0.0f ? saturate( NoL * Math::PositiveRcp( NoV ) ) : NoL;
        float c2 = 0.45f * m2 / ( m2 + 0.09f ) * cosri * a;
        float d = NoL * c1 + c2;

        return d / Math::Pi( 1.0f );
    }

    ML_INLINE float DiffuseTerm( float linearRoughness, float NoL, float NoV, float VoH )
    {
        // DiffuseTerm_Lambert
        // DiffuseTerm_Burley
        // DiffuseTerm_OrenNayar

        return DiffuseTerm_BurleyFrostbite( linearRoughness, NoL, NoV, VoH );
    }

    //======================================================================================================================
    // Distribution terms - how the microfacet normal distributed around a given direction
    //======================================================================================================================

    // [Blinn 1977, "Models of light reflection for computer synthesized pictures"]
    ML_INLINE float DistributionTerm_Blinn( float linearRoughness, float NoH )
    {
        float m = saturate( linearRoughness * linearRoughness );
        float m2 = m * m;
        float alpha = 2.0f * Math::PositiveRcp( m2 ) - 2.0f;
        float norm = ( alpha + 2.0f ) / 2.0f;
        float d = norm * Math::Pow01( NoH, alpha );

        return d / Math::Pi( 1.0f );
    }

    // [Beckmann 1963, "The scattering of electromagnetic waves from rough surfaces"]
    ML_INLINE float DistributionTerm_Beckmann( float linearRoughness, float NoH )
    {
        float m = saturate( linearRoughness * linearRoughness );
        float m2 = m * m;
        float b = NoH * NoH;
        float a = m2 * b;
        float d = exp( ( b - 1.0f ) * Math::PositiveRcp( a ) ) * Math::PositiveRcp( a * b );

        return d / Math::Pi( 1.0f );
    }

    // GGX / Trowbridge-Reitz, [Walter et al. 2007, "Microfacet models for refraction through rough surfaces"]
    ML_INLINE float DistributionTerm_GGX( float linearRoughness, float NoH )
    {
        float m = saturate( linearRoughness * linearRoughness );
        float m2 = m * m;

        #if 1
            float t = 1.0f - NoH * NoH * ( 0.99999994f - m2 );
            float a = max( m, ML_EPS ) / t;
        #else
            float t = ( NoH * m2 - NoH ) * NoH + 1.0f;
            float a = m * Math::PositiveRcp( t );
        #endif

        float d = a * a;

        return d / Math::Pi( 1.0f );
    }

    // Generalized Trowbridge-Reitz, [Burley 2012, "Physically-Based Shading at Disney"]
    ML_INLINE float DistributionTerm_GTR( float linearRoughness, float NoH )
    {
        float m = saturate( linearRoughness * linearRoughness );
        float m2 = m * m;
        float t = ( NoH * m2 - NoH ) * NoH + 1.0f;

        float t1 = Math::Pow01( t, -ML_GTR_GAMMA );
        float t2 = 1.0f - Math::Pow01( m2, -( ML_GTR_GAMMA - 1.0f ) );
        float d = ( ML_GTR_GAMMA - 1.0f ) * ( m2 * t1 - t1 ) * Math::PositiveRcp( t2 );

        return d / Math::Pi( 1.0f );
    }

    ML_INLINE float DistributionTerm( float linearRoughness, float NoH )
    {
        // DistributionTerm_Blinn
        // DistributionTerm_Beckmann
        // DistributionTerm_GGX
        // DistributionTerm_GTR

        return DistributionTerm_GGX( linearRoughness, NoH );
    }

    //======================================================================================================================
    // Geometry terms - how much the microfacet is blocked by other microfacet
    //======================================================================================================================

    // Known as "G1"
    ML_INLINE float GeometryTerm_Smith( float linearRoughness, float NoVL )
    {
        float m = saturate( linearRoughness * linearRoughness );
        float m2 = m * m;
        float a = NoVL + Math::Sqrt01( ( NoVL - m2 * NoVL ) * NoVL + m2 );

        return 2.0f * NoVL * Math::PositiveRcp( a );
    }

    //======================================================================================================================
    // Geometry terms - how much the microfacet is blocked by other microfacet
    // G(mod) = G / ( 4.0 * NoV * NoL ): BRDF = F * D * G / ( 4 * NoV * NoL ) => BRDF = F * D * Gmod
    //======================================================================================================================

    ML_INLINE float GeometryTermMod_Implicit( float linearRoughness, float NoL, float NoV, float VoH, float NoH )
    {
        ML_Unused( linearRoughness );
        ML_Unused( NoL );
        ML_Unused( NoV );
        ML_Unused( VoH );
        ML_Unused( NoH );

        return 0.25f;
    }

    // [Neumann 1999, "Compact metallic reflectance models"]
    ML_INLINE float GeometryTermMod_Neumann( float linearRoughness, float NoL, float NoV, float VoH, float NoH )
    {
        ML_Unused( linearRoughness );
        ML_Unused( VoH );
        ML_Unused( NoH );

        return 0.25f * Math::PositiveRcp( max( NoL, NoV ) );
    }

    // [Schlick 1994, "An Inexpensive BRDF Model for Physically-Based Rendering"]
    ML_INLINE float GeometryTermMod_Schlick( float linearRoughness, float NoL, float NoV, float VoH, float NoH )
    {
        ML_Unused( VoH );
        ML_Unused( NoH );

        float m = saturate( linearRoughness * linearRoughness );

        // original form
        //float k = m * sqrt( 2.0 / Math::Pi( 1.0f ) );

        // UE4: tuned to match GGX [Karis]
        float k = m * 0.5f;

        float a = NoL * ( 1.0f - k ) + k;
        float b = NoV * ( 1.0f - k ) + k;

        return 0.25f / max( a * b, ML_EPS );
    }

    // [Smith 1967, "Geometrical shadowing of a random rough surface"]
    // https://twvideo01.ubm-us.net/o1/vault/gdc2017/Presentations/Hammon_Earl_PBR_Diffuse_Lighting.pdf
    // Known as "G2 height correlated"
    ML_INLINE float GeometryTermMod_SmithCorrelated( float linearRoughness, float NoL, float NoV, float VoH, float NoH )
    {
        ML_Unused( VoH );
        ML_Unused( NoH );

        float m = saturate( linearRoughness * linearRoughness );
        float m2 = m * m;
        float a = NoV * Math::Sqrt01( ( NoL - m2 * NoL ) * NoL + m2 );
        float b = NoL * Math::Sqrt01( ( NoV - m2 * NoV ) * NoV + m2 );

        return 0.5f * Math::PositiveRcp( a + b );
    }

    // Smith term for GGX modified by Disney to be less "hot" for small roughness values
    // [Burley 2012, "Physically-Based Shading at Disney"]
    // Known as "G2 = G1( NoL ) * G1( NoV )"
    ML_INLINE float GeometryTermMod_SmithUncorrelated( float linearRoughness, float NoL, float NoV, float VoH, float NoH )
    {
        ML_Unused( VoH );
        ML_Unused( NoH );

        float m = saturate( linearRoughness * linearRoughness );
        float m2 = m * m;
        float a = NoL + Math::Sqrt01( ( NoL - m2 * NoL ) * NoL + m2 );
        float b = NoV + Math::Sqrt01( ( NoV - m2 * NoV ) * NoV + m2 );

        return Math::PositiveRcp( a * b );
    }

    // [Cook and Torrance 1982, "A Reflectance Model for Computer Graphics"]
    ML_INLINE float GeometryTermMod_CookTorrance( float linearRoughness, float NoL, float NoV, float VoH, float NoH )
    {
        ML_Unused( linearRoughness );

        float k = 2.0f * NoH / VoH;
        float a = min( k * NoV, k * NoL );

        return saturate( a ) * 0.25f * Math::PositiveRcp( NoV * NoL );
    }

    ML_INLINE float GeometryTermMod( float linearRoughness, float NoL, float NoV, float VoH, float NoH )
    {
        // GeometryTermMod_Implicit
        // GeometryTermMod_Neumann
        // GeometryTermMod_Schlick
        // GeometryTermMod_SmithCorrelated
        // GeometryTermMod_SmithUncorrelated
        // GeometryTermMod_CookTorrance

        return GeometryTermMod_SmithCorrelated( linearRoughness, NoL, NoV, VoH, NoH );
    }

    //======================================================================================================================
    // Fresnel terms - the amount of light that reflects from a mirror surface given its index of refraction
    //======================================================================================================================

    ML_INLINE float3 FresnelTerm_None( float3 Rf0, float VoNH )
    {
        ML_Unused( VoNH );

        return Rf0;
    }

    // [Schlick 1994, "An Inexpensive BRDF Model for Physically-Based Rendering"]
    ML_INLINE float3 FresnelTerm_Schlick( float3 Rf0, float VoNH )
    { return Rf0 + ( 1.0f - Rf0 ) * Pow5( VoNH ); }

    ML_INLINE float3 FresnelTerm_Fresnel( float3 Rf0, float VoNH )
    {
        float3 nu = Math::Sqrt01( Rf0 );
        nu = ( 1.0f + nu ) * Math::PositiveRcp( 1.0f - nu );

        float k = VoNH * VoNH - 1.0f;
        float3 g = sqrt( nu * nu + k );
        float3 a = ( g - VoNH ) / ( g + VoNH );
        float3 c = ( g * VoNH + k ) / ( g * VoNH - k );

        return 0.5 * a * a * ( c * c + 1.0f );
    }

    // http://www.pbr-book.org/3ed-2018/Reflection_Models/Specular_Reflection_and_Transmission.html
    // eta - relative index of refraction "from" / "to"
    ML_INLINE float FresnelTerm_Dielectric( float eta, float VoN )
    {
        float saSq = eta * eta * ( 1.0f - VoN * VoN );

        // Cosine of angle between negative normal and transmitted direction ( 0 for total internal reflection )
        float ca = Math::Sqrt01( 1.0f - saSq );

        float Rs = ( eta * VoN - ca ) * Math::PositiveRcp( eta * VoN + ca );
        float Rp = ( eta * ca - VoN ) * Math::PositiveRcp( eta * ca + VoN );

        return 0.5f * ( Rs * Rs + Rp * Rp );
    }

    ML_INLINE float3 FresnelTerm( float3 Rf0, float VoNH )
    {
        // FresnelTerm_None
        // FresnelTerm_Schlick
        // FresnelTerm_Fresnel

        return FresnelTerm_Schlick( Rf0, VoNH ) * FresnelTerm_Shadowing( Rf0 );
    }

    //======================================================================================================================
    // Environment terms ( integrated over hemisphere )
    //======================================================================================================================

    // Approximate Models For Physically Based Rendering by Angelo Pesce and Michael Iwanicki
    // http://miciwan.com/SIGGRAPH2015/course_notes_wip.pdf
    ML_INLINE float3 EnvironmentTerm_Pesce( float3 Rf0, float NoV, float linearRoughness )
    {
        float m = saturate( linearRoughness * linearRoughness );

        float a = 7.0f * NoV + 4.0f * m;
        float bias = exp2( -a );

        float b = min( linearRoughness, 0.739f + 0.323f * NoV ) - 0.434f;
        float scale = 1.0f - bias - m * max( bias, b );

        return saturate( Rf0 * scale + bias );
    }

    // Shlick's approximation for Ross BRDF - makes Fresnel converge to less than 1.0f when NoV is low
    // https://hal.inria.fr/inria-00443630/file/article-1.pdf
    ML_INLINE float3 EnvironmentTerm_Ross( float3 Rf0, float NoV, float linearRoughness )
    {
        float m = saturate( linearRoughness * linearRoughness );

        float f = Math::Pow01( 1.0f - NoV, 5.0f * exp( -2.69f * m ) ) / ( 1.0f + 22.7f * Math::Pow01( m, 1.5f ) );

        float scale = 1.0f - f;
        float bias = f;

        return saturate( Rf0 * scale + bias );
    }

#ifndef __cplusplus
    // "Ray Tracing Gems", Chapter 32, Equation 4 - the approximation assumes GGX VNDF and Schlick's approximation
    ML_INLINE float3 EnvironmentTerm_Rtg( float3 Rf0, float NoV, float linearRoughness )
    {
        float m = saturate( linearRoughness * linearRoughness );

        float4 X;
        X.x = 1.0f;
        X.y = NoV;
        X.z = NoV * NoV;
        X.w = NoV * X.z;

        float4 Y;
        Y.x = 1.0f;
        Y.y = m;
        Y.z = m * m;
        Y.w = m * Y.z;

        float2x2 M1 = float2x2( 0.99044f, -1.28514f, 1.29678f, -0.755907f );
        float3x3 M2 = float3x3( 1.0f, 2.92338f, 59.4188f, 20.3225f, -27.0302f, 222.592f, 121.563f, 626.13f, 316.627f );

        float2x2 M3 = float2x2( 0.0365463f, 3.32707f, 9.0632f, -9.04756f );
        float3x3 M4 = float3x3( 1.0f, 3.59685f, -1.36772f, 9.04401f, -16.3174f, 9.22949f, 5.56589f, 19.7886f, -20.2123f );

        float bias = dot( mul( M1, X.xy ), Y.xy ) * Math::PositiveRcp( dot( mul( M2, X.xyw ), Y.xyw ) );
        float scale = dot( mul( M3, X.xy ), Y.xy ) * Math::PositiveRcp( dot( mul( M4, X.xzw ), Y.xyw ) );

        return saturate( Rf0 * scale + bias );
    }
#endif

    ML_INLINE float3 EnvironmentTerm( float3 Rf0, float NoV, float linearRoughness )
    {
        // EnvironmentTerm_Pesce
        // EnvironmentTerm_Ross
        // EnvironmentTerm_Unknown

        return EnvironmentTerm_Ross( Rf0, NoV, linearRoughness ) * FresnelTerm_Shadowing( Rf0 );
    }

    //======================================================================================================================
    // Direct lighting
    //======================================================================================================================

    ML_INLINE void DirectLighting( float3 N, float3 L, float3 V, float3 Rf0, float linearRoughness, ML_OUT(float3) Cdiff, ML_OUT(float3) Cspec )
    {
        float3 H = normalize( L + V );

        float NoL = saturate( dot( N, L ) );
        float NoH = saturate( dot( N, H ) );
        float VoH = saturate( dot( V, H ) );

        // Due to normal mapping can easily be < 0, it blows up GeometryTerm (Smith)
        float NoV = abs( dot( N, V ) );

        float D = DistributionTerm( linearRoughness, NoH );
        float G = GeometryTermMod( linearRoughness, NoL, NoV, VoH, NoH );
        float3 F = FresnelTerm( Rf0, VoH );
        float Kdiff = DiffuseTerm( linearRoughness, NoL, NoV, VoH );

        Cspec = F * D * G * NoL;
        Cdiff = ( 1.0f - F ) * Kdiff * NoL;

        Cspec = saturate( Cspec );
    }
}

//=======================================================================================================================
// IMPORTANCE SAMPLING
//=======================================================================================================================

namespace ImportanceSampling
{
    // Defines a cone angle, where micro-normals are distributed
    // [Lagarde 2014, "Moving Frostbite to Physically Based Rendering 3.0"]
    // Formula with typo:
    //      https://seblagarde.files.wordpress.com/2015/07/course_notes_moving_frostbite_to_pbr_v32.pdf (page 72)
    // Correct formula is here:
    //      https://seblagarde.wordpress.com/2015/07/14/siggraph-2014-moving-frostbite-to-physically-based-rendering/ (4-9-3-DistanceBasedRoughnessLobeBounding.pdf, page 3)
    // https://www.desmos.com/calculator/mv1fteycal
    ML_INLINE float GetSpecularLobeTanHalfAngle( float linearRoughness, float percentOfVolume = 0.75 )
    {
        percentOfVolume = saturate( percentOfVolume );

        return saturate( linearRoughness ) * sqrt( percentOfVolume / ( 1.0f - percentOfVolume + ML_EPS ) );
    }

    // TODO: add tube & rect lights, move the function to this section
    ML_INLINE float3 CorrectDirectionToInfiniteSource( float3 N, float3 L, float3 V, float tanOfAngularSize )
    {
        float3 R = reflect( -V, N );
        float3 centerToRay = L - dot( L, R ) * R;
        float3 closestPoint = centerToRay * saturate( tanOfAngularSize * Math::Rsqrt( Math::LengthSquared( centerToRay ) ) );

        return normalize( L - closestPoint );
    }

    // [Lagarde 2014, "Moving Frostbite to Physically Based Rendering 3.0"]
    // https://seblagarde.files.wordpress.com/2015/07/course_notes_moving_frostbite_to_pbr_v32.pdf (page 69)
    #define ML_SPECULAR_DOMINANT_DIRECTION_G1      0
    #define ML_SPECULAR_DOMINANT_DIRECTION_G2      1
    #define ML_SPECULAR_DOMINANT_DIRECTION_APPROX  2

    ML_INLINE float GetSpecularDominantFactor( float NoV, float linearRoughness, compiletime const uint mode = ML_SPECULAR_DOMINANT_DIRECTION_DEFAULT )
    {
        linearRoughness = saturate( linearRoughness );

        float dominantFactor;
        if( mode == ML_SPECULAR_DOMINANT_DIRECTION_G2 )
        {
            float a = 0.298475f * log( 39.4115f - 39.0029f * linearRoughness );
            dominantFactor = Math::Pow01( 1.0f - NoV, 10.8649f ) * ( 1.0f - a ) + a;
        }
        else if( mode == ML_SPECULAR_DOMINANT_DIRECTION_G1 )
            dominantFactor = 0.298475f * NoV * log( 39.4115f - 39.0029f * linearRoughness ) + ( 0.385503f - 0.385503f * NoV ) * log( 13.1567f - 12.2848f * linearRoughness );
        else
        {
            float s = 1.0f - linearRoughness;
            dominantFactor = s * ( Math::Sqrt01( s ) + linearRoughness );
        }

        return saturate( dominantFactor );
    }

    ML_INLINE float3 GetSpecularDominantDirectionWithFactor( float3 N, float3 V, float dominantFactor )
    {
        float3 R = reflect( -V, N );
        float3 D = lerp( N, R, dominantFactor );

        return normalize( D );
    }

    ML_INLINE float4 GetSpecularDominantDirection( float3 N, float3 V, float linearRoughness, compiletime const uint mode = ML_SPECULAR_DOMINANT_DIRECTION_DEFAULT )
    {
        float NoV = abs( dot( N, V ) );
        float dominantFactor = GetSpecularDominantFactor( NoV, linearRoughness, mode );

        return float4( GetSpecularDominantDirectionWithFactor( N, V, dominantFactor ), dominantFactor );
    }

    //=================================================================================
    // Uniform
    //=================================================================================

    namespace Uniform
    {
        ML_INLINE float GetPDF( )
        { return 1.0f / Math::Pi( 2.0 ); }

        ML_INLINE float3 GetRay( float2 rnd )
        {
            float phi = rnd.x * Math::Pi( 2.0 );

            float cosTheta = rnd.y;
            float sinTheta = Math::Sqrt01( 1.0f - cosTheta * cosTheta );

            float3 ray;
            ray.x = sinTheta * cos( phi );
            ray.y = sinTheta * sin( phi );
            ray.z = cosTheta;

            return ray;
        }
    }

    //=================================================================================
    // Cosine
    //=================================================================================

    namespace Cosine
    {
        ML_INLINE float GetPDF( float NoL = 1.0f ) // default can be useful to handle NoL cancelation ( PDF's NoL cancels throughput's NoL )
        {
            float pdf = NoL / Math::Pi( 1.0f );

            return max( pdf, ML_EPS );
        }

        ML_INLINE float3 GetRay( float2 rnd )
        {
            float phi = rnd.x * Math::Pi( 2.0f );

            float cosTheta = Math::Sqrt01( rnd.y );
            float sinTheta = Math::Sqrt01( 1.0f - cosTheta * cosTheta );

            float3 ray;
            ray.x = sinTheta * cos( phi );
            ray.y = sinTheta * sin( phi );
            ray.z = cosTheta;

            return ray;
        }
    }

    //=================================================================================
    // GGX-NDF
    //=================================================================================

    namespace NDF
    {
        ML_INLINE float GetPDF( float linearRoughness, float NoH, float VoH )
        {
            float pdf = BRDF::DistributionTerm_GGX( linearRoughness, NoH );
            pdf *= NoH;
            pdf *= Math::PositiveRcp( 4.0f * VoH );

            return max( pdf, ML_EPS );
        }

        ML_INLINE float3 GetRay( float2 rnd, float linearRoughness )
        {
            float m = saturate( linearRoughness * linearRoughness );
            float m2 = m * m;
            float t = ( m2 - 1.0f ) * rnd.y + 1.0f;
            float cosThetaSq = ( 1.0f - rnd.y ) * Math::PositiveRcp( t );
            float sinTheta = Math::Sqrt01( 1.0f - cosThetaSq );
            float phi = rnd.x * Math::Pi( 2.0f );

            float3 ray;
            ray.x = sinTheta * cos( phi );
            ray.y = sinTheta * sin( phi );
            ray.z = Math::Sqrt01( cosThetaSq );

            return ray;
        }
    }

    //=================================================================================
    // GGX-VNDF
    // ML_VNDF_VERSION == 1: http://jcgt.org/published/0007/04/01/paper.pdf
    // ML_VNDF_VERSION == 2: https://diglib.eg.org/bitstream/handle/10.1111/cgf14867/v42i8_03_14867.pdf
    // ML_VNDF_VERSION == 3: https://gpuopen.com/download/publications/Bounded_VNDF_Sampling_for_Smith-GGX_Reflections.pdf
    //=================================================================================

    namespace VNDF
    {
        ML_INLINE float GetPDF( float3 Vlocal, float NoH, float linearRoughness )
        {
            float2 m = saturate( linearRoughness * linearRoughness );

            float a = min( m.x, m.y );
            float a2 = a * a;

            float D = BRDF::DistributionTerm_GGX( linearRoughness, NoH );

            #if( ML_VNDF_VERSION == 1 )
                /*
                Eq 3  : Dv( H ) = G1 * D * VoH / NoV
                Eq 17 : PDF = Dv( H ) / ( 4 * VoH )

                Simplification:
                    G1 = BRDF::GeometryTerm_Smith( linearRoughness, NoV )
                    D = BRDF::DistributionTerm_GGX( linearRoughness, NoH )

                    m2 = m * m
                    G1mod = 1 / [ NoV + Math::Sqrt01( ( NoV - m2 * NoV ) * NoV + m2 ) ]
                    G1 = 2 * G1mod * NoV

                    => PDF = ( 2 * G1mod * NoV * D * VoH / NoV ) / ( 4 * VoH )
                    => PDF = ( 2 * G1mod * D * VoH ) / ( 4 * VoH )
                    => PDF = ( 2 * G1mod * D ) / 4
                    => PDF = ( G1mod * D ) / 2
                */
                float G1mod = Math::PositiveRcp( Vlocal.z + Math::Sqrt01( ( Vlocal.z - a2 * Vlocal.z ) * Vlocal.z + a2 ) ); // see GeometryTerm_Smith

                return 0.5 * G1mod * D;
            #else
                float2 wi = m * Vlocal.xy;
                float lenSq = dot(wi, wi);
                float t = sqrt(lenSq + Vlocal.z * Vlocal.z);

                if( Vlocal.z < 0.0f )
                    return 0.5f * D * ( t - Vlocal.z ) / lenSq;

                #if( ML_VNDF_VERSION == 3 )
                    float s = 1.0f + length( Vlocal.xy );
                    float s2 = s * s;
                    float k = ( 1.0f - a2 ) * s2 / ( s2 + a2 * Vlocal.z * Vlocal.z );
                #else
                    float k = 1.0f;
                #endif

                return 0.5f * D / ( k * Vlocal.z + t );
            #endif
        }

        ML_INLINE float3 GetRay( float2 rnd, float2 linearRoughness, float3 Vlocal, float trimFactor = 1.0f )
        {
            /*
            Trimming:
                0.0  - dominant direction
                1.0f  - full lobe
                0.95 - allows to cut off samples with very low probabilities ( good for denoising )
            */
            rnd.y *= trimFactor;

            // TODO: instead of using 2 roughness values introduce "anisotropy" parameter
            // https://blog.selfshadow.com/publications/s2013-shading-course/rad/s2013_pbs_rad_notes.pdf (page 3)
            float2 m = saturate( linearRoughness * linearRoughness );

            // Warp to the hemisphere configuration
            float3 wi = normalize( float3( m * Vlocal.xy, Vlocal.z ) );

            float phi = Math::Pi( 2.0f ) * rnd.x;
            #if( ML_VNDF_VERSION == 1 )
                float lenSq = dot( wi.xy, wi.xy );
                float3 X = lenSq > ML_EPS ? float3( -wi.y, wi.x, 0.0 ) * rsqrt( lenSq ) : float3( 1.0, 0.0, 0.0 );
                float3 Y = cross( wi, X );

                float z = 0.5 * ( 1.0f + wi.z );
                float r = Math::Sqrt01( rnd.y );
                float x = r * cos( phi );
                float y = lerp( Math::Sqrt01( 1.0f - x * x ), r * sin( phi ), z );

                float3 h = x * X + y * Y + Math::Sqrt01( 1.0f - x * x - y * y ) * wi;
            #else
                #if( ML_VNDF_VERSION == 2 )
                    float b = wi.z;
                #elif( ML_VNDF_VERSION == 3 )
                    float a = min( m.x, m.y );
                    float s = 1.0f + length( Vlocal.xy );
                    float a2 = a * a;
                    float s2 = s * s;
                    float k = ( 1.0f - a2 ) * s2 / ( s2 + a2 * Vlocal.z * Vlocal.z );
                    float b = Vlocal.z > 0.0f ? k * wi.z : wi.z;
                #endif

                float z = 1.0f - rnd.y * ( 1.0f + b );
                float r = Math::Sqrt01( 1.0f - z * z );
                float x = r * cos( phi );
                float y = r * sin( phi );

                float3 h = float3( x, y, z ) + wi;
            #endif

            // Warp back to the ellipsoid configuration
            return normalize( float3( m * h.xy, max( h.z, ML_EPS ) ) );
        }
    }
}

//=======================================================================================================================
// SPHERICAL HARMONICS
//=======================================================================================================================

// https://media.contentapi.ea.com/content/dam/eacom/frostbite/files/gdc2018-precomputedgiobalilluminationinfrostbite.pdf

struct SH1
{
    float3 c0_chroma;
    float3 c1;
};

namespace SphericalHarmonics
{
    ML_INLINE SH1 ConvertToSecondOrder( float3 color, float3 direction )
    {
        float3 YCoCg = Color::RgbToYCoCg( color );

        SH1 sh;
        sh.c0_chroma = YCoCg;
        sh.c1 = YCoCg.x * direction;

        return sh;
    }

    ML_INLINE float3 ExtractColor( SH1 sh )
    {
        return Color::YCoCgToRgb( sh.c0_chroma );
    }

    ML_INLINE float3 ExtractDirection( SH1 sh )
    {
        return sh.c1 * Math::Rsqrt( Math::LengthSquared( sh.c1 ) );
    }

    ML_INLINE void Add( ML_INOUT( SH1 ) result, SH1 x )
    {
        result.c0_chroma += x.c0_chroma;
        result.c1 += x.c1;
    }

    ML_INLINE void Mul( ML_INOUT( SH1 ) result, float x )
    {
        result.c0_chroma *= x;
        result.c1 *= x;
    }

    ML_INLINE float3 ResolveColor( SH1 sh, float3 N )
    {
        float Y = 0.5f * dot( N, sh.c1 ) + 0.25f * sh.c0_chroma.x;

        // 2 - hemisphere, 4 - sphere
        Y *= 2.0f;

        // Corrected color reproduction
        Y = max( Y, 0.0f );

        float modifier = ( Y + ML_EPS ) / ( sh.c0_chroma.x + ML_EPS );
        float2 CoCg = modifier * sh.c0_chroma.yz;

        return Color::YCoCgToRgb( float3( Y, CoCg ) );
    }
}

//=======================================================================================================================
// TEXT
//=======================================================================================================================

#ifndef __cplusplus
namespace Text
{
    //===================================================================================================================
    // Constants
    //===================================================================================================================

    static const uint Char_0            = 0;
    static const uint Char_Minus        = 10;
    static const uint Char_Dot          = 11;
    static const uint Char_Space        = 12;
    static const uint Char_Ampersand    = 13;
    static const uint Char_A            = 14;

    //===================================================================================================================
    // Private
    //===================================================================================================================

    static const uint CHAR_W            = 5;
    static const uint CHAR_H            = 6;

    static const uint BACKGROUND        = 1;
    static const uint FOREGROUND        = 2;

    #define X                           1
    #define _                           0

#if( ML_WINDOW_ORIGIN_OGL == 1 )
    #define CHAR( a1, a2, a3, a4, a5, \
                  b1, b2, b3, b4, b5, \
                  c1, c2, c3, c4, c5, \
                  d1, d2, d3, d4, d5, \
                  e1, e2, e3, e4, e5, \
                  f1, f2, f3, f4, f5 )      ( ( f1 <<  0 ) | ( f2 <<  1 ) | ( f3 <<  2 ) | ( f4 <<  3 ) | ( f5 <<  4 ) | \
                                              ( e1 <<  5 ) | ( e2 <<  6 ) | ( e3 <<  7 ) | ( e4 <<  8 ) | ( e5 <<  9 ) | \
                                              ( d1 << 10 ) | ( d2 << 11 ) | ( d3 << 12 ) | ( d4 << 13 ) | ( d5 << 14 ) | \
                                              ( c1 << 15 ) | ( c2 << 16 ) | ( c3 << 17 ) | ( c4 << 18 ) | ( c5 << 19 ) | \
                                              ( b1 << 20 ) | ( b2 << 21 ) | ( b3 << 22 ) | ( b4 << 23 ) | ( b5 << 24 ) | \
                                              ( a1 << 25 ) | ( a2 << 26 ) | ( a3 << 27 ) | ( a4 << 28 ) | ( a5 << 29 ) )
#else
    #define CHAR( a1, a2, a3, a4, a5, \
                  b1, b2, b3, b4, b5, \
                  c1, c2, c3, c4, c5, \
                  d1, d2, d3, d4, d5, \
                  e1, e2, e3, e4, e5, \
                  f1, f2, f3, f4, f5 )      ( ( a1 <<  0 ) | ( a2 <<  1 ) | ( a3 <<  2 ) | ( a4 <<  3 ) | ( a5 <<  4 ) | \
                                              ( b1 <<  5 ) | ( b2 <<  6 ) | ( b3 <<  7 ) | ( b4 <<  8 ) | ( b5 <<  9 ) | \
                                              ( c1 << 10 ) | ( c2 << 11 ) | ( c3 << 12 ) | ( c4 << 13 ) | ( c5 << 14 ) | \
                                              ( d1 << 15 ) | ( d2 << 16 ) | ( d3 << 17 ) | ( d4 << 18 ) | ( d5 << 19 ) | \
                                              ( e1 << 20 ) | ( e2 << 21 ) | ( e3 << 22 ) | ( e4 << 23 ) | ( e5 << 24 ) | \
                                              ( f1 << 25 ) | ( f2 << 26 ) | ( f3 << 27 ) | ( f4 << 28 ) | ( f5 << 29 ) )
#endif

    static const uint font[ ] =
    {
        CHAR( _, X, X, X, _,
                X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X,
                _, X, X, X, _ ),

        CHAR( _, _, _, _, X,
                _, _, _, X, X,
                _, _, _, _, X,
                _, _, _, _, X,
                _, _, _, _, X,
                _, _, _, _, X ),

        CHAR( X, X, X, X, _,
                _, _, _, _, X,
                X, X, X, X, X,
                X, _, _, _, _,
                X, _, _, _, _,
                X, X, X, X, X ),

        CHAR( X, X, X, X, _,
                _, _, _, _, X,
                _, X, X, X, X,
                _, _, _, _, X,
                _, _, _, _, X,
                X, X, X, X, _ ),

        CHAR( X, _, _, _, X,
                X, _, _, _, X,
                X, X, X, X, X,
                _, _, _, _, X,
                _, _, _, _, X,
                _, _, _, _, X ),

        CHAR( X, X, X, X, _,
                X, _, _, _, _,
                X, X, X, X, X,
                _, _, _, _, X,
                _, _, _, _, X,
                X, X, X, X, _ ),

        CHAR( _, X, X, X, X,
                X, _, _, _, _,
                X, X, X, X, X,
                X, _, _, _, X,
                X, _, _, _, X,
                X, X, X, X, _ ),

        CHAR( _, X, X, X, _,
                _, _, _, _, X,
                _, _, _, _, X,
                _, _, _, _, X,
                _, _, _, _, X,
                _, _, _, _, X ),

        CHAR( _, X, X, X, _,
                X, _, _, _, X,
                X, X, X, X, X,
                X, _, _, _, X,
                X, _, _, _, X,
                _, X, X, X, _ ),

        CHAR( _, X, X, X, _,
                X, _, _, _, X,
                X, X, X, X, X,
                _, _, _, _, X,
                _, _, _, _, X,
                X, X, X, X, _ ),

        CHAR( _, _, _, _, _,
                _, _, _, _, _,
                X, X, X, X, X,
                _, _, _, _, _,
                _, _, _, _, _,
                _, _, _, _, _ ),

        CHAR( _, _, _, _, _,
                _, _, _, _, _,
                _, _, _, _, _,
                _, _, _, _, _,
                _, _, _, _, _,
                _, _, X, _, _ ),

        CHAR( _, _, _, _, _,
                _, _, _, _, _,
                _, _, _, _, _,
                _, _, _, _, _,
                _, _, _, _, _,
                _, _, _, _, _ ),

        CHAR( _, _, X, _, _,
                _, X, _, X, _,
                _, _, X, _, _,
                _, X, _, X, _,
                X, _, _, X, _,
                _, X, X, _, X ),

        CHAR( _, _, X, X, X,
                _, X, _, _, X,
                X, _, _, _, X,
                X, X, X, X, X,
                X, _, _, _, X,
                X, _, _, _, X ),

        CHAR( X, X, X, X, _,
                X, _, _, _, X,
                X, X, X, X, _,
                X, _, _, _, X,
                X, _, _, _, X,
                X, X, X, X, _ ),

        CHAR( _, X, X, X, X,
                X, _, _, _, _,
                X, _, _, _, _,
                X, _, _, _, _,
                X, _, _, _, _,
                _, X, X, X, X ),

        CHAR( X, X, X, X, _,
                X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X,
                X, X, X, X, _ ),

        CHAR( X, X, X, X, X,
                X, _, _, _, _,
                X, X, X, X, _,
                X, _, _, _, _,
                X, _, _, _, _,
                X, X, X, X, X ),

        CHAR( X, X, X, X, X,
                X, _, _, _, _,
                X, X, X, X, _,
                X, _, _, _, _,
                X, _, _, _, _,
                X, _, _, _, _ ),

        CHAR( _, X, X, X, X,
                X, _, _, _, _,
                X, _, _, _, _,
                X, _, _, X, X,
                X, _, _, _, X,
                _, X, X, X, X ),

        CHAR( X, _, _, _, X,
                X, _, _, _, X,
                X, X, X, X, X,
                X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X ),

        CHAR( _, X, X, X, _,
                _, _, X, _, _,
                _, _, X, _, _,
                _, _, X, _, _,
                _, _, X, _, _,
                _, X, X, X, _ ),

        CHAR( _, _, _, _, X,
                _, _, _, _, X,
                _, _, _, _, X,
                _, _, _, _, X,
                X, _, _, _, X,
                _, X, X, X, _ ),

        CHAR( X, _, _, _, X,
                X, _, _, X, _,
                X, X, X, _, _,
                X, _, _, X, _,
                X, _, _, _, X,
                X, _, _, _, X ),

        CHAR( X, _, _, _, _,
                X, _, _, _, _,
                X, _, _, _, _,
                X, _, _, _, _,
                X, _, _, _, _,
                X, X, X, X, X ),

        CHAR( X, _, _, _, X,
                X, X, _, X, X,
                X, _, X, _, X,
                X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X ),

        CHAR( X, _, _, _, X,
                X, X, _, _, X,
                X, _, X, _, X,
                X, _, _, X, X,
                X, _, _, _, X,
                X, _, _, _, X ),

        CHAR( _, X, X, X, _,
                X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X,
                _, X, X, X, _ ),

        CHAR( X, X, X, X, _,
                X, _, _, _, X,
                X, _, _, _, X,
                X, X, X, X, _,
                X, _, _, _, _,
                X, _, _, _, _ ),

        CHAR( _, X, X, X, _,
                X, _, _, _, X,
                X, _, _, _, X,
                X, _, X, _, X,
                X, _, _, X, _,
                _, X, X, _, X ),

        CHAR( X, X, X, X, _,
                X, _, _, _, X,
                X, _, _, _, X,
                X, X, X, X, _,
                X, _, _, X, _,
                X, _, _, _, X ),

        CHAR( _, X, X, X, X,
                X, _, _, _, _,
                _, X, X, X, _,
                _, _, _, _, X,
                _, _, _, _, X,
                X, X, X, X, _ ),

        CHAR( X, X, X, X, X,
                _, _, X, _, _,
                _, _, X, _, _,
                _, _, X, _, _,
                _, _, X, _, _,
                _, _, X, _, _ ),

        CHAR( X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X,
                _, X, X, X, _ ),

        CHAR( X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X,
                X, _, _, _, X,
                _, X, _, X, _,
                _, _, X, _, _ ),

        CHAR( X, _, _, _, X,
                X, _, _, _, X,
                X, _, X, _, X,
                X, _, X, _, X,
                X, X, X, X, X,
                _, X, _, X, _ ),

        CHAR( X, _, _, _, X,
                _, X, _, X, _,
                _, _, X, _, _,
                _, X, _, X, _,
                X, _, _, _, X,
                X, _, _, _, X ),

        CHAR( X, _, _, _, X,
                _, X, _, X, _,
                _, X, _, X, _,
                _, _, X, _, _,
                _, _, X, _, _,
                _, _, X, _, _ ),

        CHAR( X, X, X, X, X,
                _, _, _, X, _,
                _, _, X, _, _,
                _, X, _, _, _,
                X, _, _, _, _,
                X, X, X, X, X ),
    };

    #undef CHAR
    #undef _
    #undef X

    #if( ML_TEXT_WITH_NICE_ONE_PIXEL_BACKGROUND == 1 )

        #define _RenderChar( ch )  \
            if( all( int2( state.xy ) >= -int( state.z ) && int2( state.xy ) < int2( CHAR_W + 1, CHAR_H + 1 ) * int( state.z ) ) ) \
            { \
                state.w = BACKGROUND; \
                if( all( state.xy < uint2( CHAR_W, CHAR_H ) * state.z ) ) \
                { \
                    uint2 p = state.xy / state.z; \
                    uint bits = font[ ch ]; \
                    uint bit = bits & ( 1u << ( p.y * CHAR_W + p.x ) ); \
                    state.w = bit ? FOREGROUND : BACKGROUND; \
                } \
            }

    #else

        #define _RenderChar( ch )  \
            if( all( state.xy < uint2( CHAR_W, CHAR_H ) * state.z ) ) \
            { \
                uint2 p = state.xy / state.z; \
                uint bits = font[ ch ]; \
                uint bit = bits & ( 1u << ( p.y * CHAR_W + p.x ) ); \
                state.w = bit ? FOREGROUND : BACKGROUND; \
            }

    #endif

    //===================================================================================================================
    // Interface
    //===================================================================================================================

    ML_INLINE uint4 Init( uint2 pixelPos, uint2 origin, uint scale )
    {
        uint4 state;
        state.xy = pixelPos - origin;
        state.z = scale;
        state.w = 0;

        return state;
    }

    ML_INLINE bool IsBackground( uint4 state )
    { return state.w == BACKGROUND; }

    ML_INLINE bool IsForeground( uint4 state )
    { return state.w == FOREGROUND; }

    ML_INLINE void NextChar( ML_INOUT( uint4 ) state )
    { state.x -= ( CHAR_W + 1 ) * state.z; }

    ML_INLINE void NextDigit( ML_INOUT( uint4 ) state )
    { state.x += ( CHAR_W + 1 ) * state.z; }

    ML_INLINE void Print_ui( uint x, ML_INOUT( uint4 ) state )
    {
        while( x )
        {
            uint a = x / 10;
            uint digit = x - a * 10;

            NextDigit( state );
            _RenderChar( digit );

            x = a;
        }
    }

    ML_INLINE void Print_i( int x, ML_INOUT( uint4 ) state )
    {
        // Absolute value
        Print_ui( abs( x ), state );

        // Minus
        if( x < 0 )
        {
            NextDigit( state );
            _RenderChar( Char_Minus );
        }
    }

    ML_INLINE void Print_f( float x, ML_INOUT( uint4 ) state )
    {
        // Fractional part
        uint f = uint( frac( abs( x ) ) * ML_TEXT_DIGIT_FORMAT + 0.5 );
        Print_ui( f, state );

        // Zeros after dot
        [unroll]
        for( uint n = 10; n < ML_TEXT_DIGIT_FORMAT; n *= 10 )
        {
            if( f < n )
            {
                NextDigit( state );
                _RenderChar( Char_0 );
            }
        }

        // Dot
        NextDigit( state );
        _RenderChar( Char_Dot );

        // Integer part
        int i = int( floor( x ) + 0.5 );
        Print_i( i, state );
    }

    ML_INLINE void Print_ch( uint ch, ML_INOUT( uint4 ) state )
    {
        if( ch == Char_Minus || ch == '-' )
            ch = Char_Minus;
        else if( ch == Char_Dot || ch == '.' )
            ch = Char_Dot;
        else if( ch == Char_Space || ch == ' ' )
            ch = Char_Space;
        else if( ch == Char_Ampersand || ch == '&' )
            ch = Char_Ampersand;
        else
            ch = Char_A + ch - 'A';

        _RenderChar( ch );
        NextChar( state );
    }
}
#endif

#ifdef ML_NAMESPACE
}
#endif

#endif