// The following methods are described in this article:
// http://chilliant.blogspot.com/2012/08/srgb-approximations-for-hlsl.html

// The following 4 methods are the most accurate approximations
vec3 qt_linearTosRGB(vec3 color)
{
    vec3 S1 = sqrt(color);
    vec3 S2 = sqrt(S1);
    vec3 S3 = sqrt(S2);
    return 0.585122381 * S1 + 0.783140355 * S2 - 0.368262736 * S3;
}

vec3 qt_sRGBToLinear(vec3 srgbIn)
{
    return srgbIn * (srgbIn * (srgbIn * 0.305306011 + 0.682171111) + 0.012522878);
}

vec4 qt_linearTosRGB(vec4 color)
{
    return vec4(qt_linearTosRGB(color.rgb), color.a);
}

vec4 qt_sRGBToLinear(vec4 srgbIn)
{
    return vec4(qt_sRGBToLinear(srgbIn.rgb), srgbIn.a);
}

const float GAMMA = 2.2;
const float INV_GAMMA = 1.0 / GAMMA;

// The following 4 methods are the fastest, but less accurate

vec3 qt_linearTosRGBFast(vec3 color)
{
    return pow(color, vec3(INV_GAMMA));
}

vec3 qt_sRGBToLinearFast(vec3 srgbIn)
{
    return vec3(pow(srgbIn.xyz, vec3(GAMMA)));
}

vec4 qt_linearTosRGBFast(vec4 color)
{
    return vec4(pow(color.rgb, vec3(INV_GAMMA)), color.a);
}

vec4 qt_sRGBToLinearFast(vec4 srgbIn)
{
    return vec4(pow(srgbIn.rgb, vec3(GAMMA)), srgbIn.a);
}


#ifndef QSSG_ENABLE_LINEAR_TONEMAPPING
#define QSSG_ENABLE_LINEAR_TONEMAPPING 0
#endif
#ifndef QSSG_ENABLE_ACES_TONEMAPPING
#define QSSG_ENABLE_ACES_TONEMAPPING 0
#endif
#ifndef QSSG_ENABLE_HEJLDAWSON_TONEMAPPING
#define QSSG_ENABLE_HEJLDAWSON_TONEMAPPING 0
#endif
#ifndef QSSG_ENABLE_FILMIC_TONEMAPPING
#define QSSG_ENABLE_FILMIC_TONEMAPPING 0
#endif

#if QSSG_ENABLE_ACES_TONEMAPPING
vec3 qt_toneMapACES(vec3 color)
{
    const float A = 2.51;
    const float B = 0.03;
    const float C = 2.43;
    const float D = 0.59;
    const float E = 0.14;
    return qt_linearTosRGB(clamp((color * (A * color + B)) / (color * (C * color + D) + E), 0.0, 1.0));
}
#endif

#if QSSG_ENABLE_HEJLDAWSON_TONEMAPPING
vec3 qt_tonemapHejlDawson(vec3 color)
{
    color = max(vec3(0.0), color - vec3(0.004));
    return (color * (6.2 * color + 0.5)) / (color * (6.2 * color + 1.7) + 0.06);
}
#endif

#if QSSG_ENABLE_FILMIC_TONEMAPPING
vec3 qt_toneMapFilmicSub(vec3 color)
{
    const float A = 0.15;
    const float B = 0.50;
    const float C = 0.10;
    const float D = 0.20;
    const float E = 0.02;
    const float F = 0.30;
    return ((color * ( A * color + C * B) + D * E) / (color * (A * color + B) + D * F)) - E / F;
}

vec3 qt_toneMapFilmic(vec3 color)
{
    color = qt_toneMapFilmicSub(color * 2.0);
    vec3 whiteScale = 1.0 / qt_toneMapFilmicSub(vec3(11.2, 11.2, 11.2));
    return qt_linearTosRGB(color * whiteScale);
}
#endif

// Call this method to perform tonemapping with the correct tonemapper
vec3 qt_tonemap(vec3 color)
{
    // ACES
#if QSSG_ENABLE_ACES_TONEMAPPING
    return qt_toneMapACES(color);
#endif
    // Hejl-Dawson
#if QSSG_ENABLE_HEJLDAWSON_TONEMAPPING
    return qt_tonemapHejlDawson(color);
#endif

    // Filmic
#if QSSG_ENABLE_FILMIC_TONEMAPPING
    return qt_toneMapFilmic(color);
#endif

    // Linear
#if QSSG_ENABLE_LINEAR_TONEMAPPING
    return qt_linearTosRGB(color);
#endif

    return color;
}

vec4 qt_tonemap(vec4 color)
{
    return vec4(qt_tonemap(color.rgb), color.a);
}
