Function SunLuminance

BakingLab/AppSettings.cpp:713–804

    }

    Float3 SunLuminance(bool& cached)
    {
        Float3 sunDirection = AppSettings::SunDirection;
        sunDirection.y = Saturate(sunDirection.y);
        sunDirection = Float3::Normalize(sunDirection);
        const float turbidity = Clamp(AppSettings::Turbidity.Value(), 1.0f, 32.0f);
        const float intensityScale = AppSettings::SunIntensityScale;
        const Float3 tintColor = AppSettings::SunTintColor;
        const bool32 normalizeIntensity = AppSettings::NormalizeSunIntensity;
        const float sunSize = AppSettings::SunSize;

        static float turbidityCache = 2.0f;
        static Float3 sunDirectionCache = Float3(-0.579149902f, 0.754439294f, -0.308879942f);
        static Float3 luminanceCache = Float3(1.61212531e+009f, 1.36822630e+009f, 1.07235315e+009f) * FP16Scale;
        static Float3 sunTintCache = Float3(1.0f, 1.0f, 1.0f);
        static float sunIntensityCache = 1.0f;
        static bool32 normalizeCache = false;
        static float sunSizeCache = AppSettings::BaseSunSize;

        if(turbidityCache == turbidity && sunDirection == sunDirectionCache
            && intensityScale == sunIntensityCache && tintColor == sunTintCache
            && normalizeCache == normalizeIntensity && sunSize == sunSizeCache)
        {
            cached = true;
            return luminanceCache;
        }

        cached = false;

        float thetaS = std::acos(1.0f - sunDirection.y);
        float elevation = Pi_2 - thetaS;

        // Get the sun's luminance, then apply tint and scale factors
        Float3 sunLuminance;

        // For now, we'll compute an average luminance value from Hosek solar radiance model, even though
        // we could compute illuminance directly while we're sampling the disk
        SampledSpectrum groundAlbedoSpectrum = SampledSpectrum::FromRGB(GroundAlbedo);
        SampledSpectrum solarRadiance;

        const uint64 NumDiscSamples = 8;
        for(uint64 x = 0; x < NumDiscSamples; ++x)
        {
            for(uint64 y = 0; y < NumDiscSamples; ++y)
            {
                float u = (x + 0.5f) / NumDiscSamples;
                float v = (y + 0.5f) / NumDiscSamples;
                Float2 discSamplePos = SquareToConcentricDiskMapping(u, v);

                float theta = elevation + discSamplePos.y * DegToRad(AppSettings::BaseSunSize);
                float gamma = discSamplePos.x * DegToRad(AppSettings::BaseSunSize);

                for(int32 i = 0; i < NumSpectralSamples; ++i)
                {
                    ArHosekSkyModelState* skyState = arhosekskymodelstate_alloc_init(elevation, turbidity, groundAlbedoSpectrum[i]);
                    float wavelength = Lerp(float(SampledLambdaStart), float(SampledLambdaEnd), i / float(NumSpectralSamples));

                    solarRadiance[i] = float(arhosekskymodel_solar_radiance(skyState, theta, gamma, wavelength));