Function SampleSphericalAreaLight

BakingLab/PathTracer.cpp:112–161

Calculates diffuse and specular from a spherical area light

// Calculates diffuse and specular from a spherical area light
static Float3 SampleSphericalAreaLight(const Float3& position, const Float3& normal, RTCScene scene,
                                       const Float3& diffuseAlbedo, const Float3& cameraPos,
                                       bool includeSpecular, Float3 specAlbedo, float roughness,
                                       float u1, float u2, float lightRadius,
                                       const Float3& lightPos, const Float3& lightColor, Float3& irradiance)
{
    const float radius2 = lightRadius * lightRadius;
    const float invPDF = 2.0f * Pi * radius2;

    Float3 result = 0.0f;
    Float3 areaLightIrradiance = 0.0f;

    float r = lightRadius;
    float x = u1;
    float y = u2;

    Float3 samplePos;
    samplePos.x = lightPos.x + 2.0f * r * std::cos(2.0f * Pi * y) * std::sqrt(x * (1.0f - x));
    samplePos.y = lightPos.y + 2.0f * r * std::sin(2.0f * Pi * y) * std::sqrt(x * (1.0f - x));
    samplePos.z = lightPos.z + r * (1.0f - 2.0f * x);

    Float3 sampleDir = samplePos - position;
    float sampleDirLen = Float3::Length(sampleDir);
    bool visible = false;
    if(sampleDirLen > 0.0f)
    {
        sampleDir /= sampleDirLen;

        visible = Occluded(scene, position, sampleDir, 0.1f, sampleDirLen) == false;
    }

    float areaNDotL = std::abs(Float3::Dot(sampleDir, Float3::Normalize(samplePos - lightPos)));
    float sDotN = Saturate(Float3::Dot(sampleDir, normal));

    float invRSqr = 1.0f / (sampleDirLen * sampleDirLen);

    float attenuation = areaNDotL * invRSqr;
    if(attenuation && visible)
    {
        Float3 sampleIrradiance = Saturate(Float3::Dot(normal, sampleDir)) * lightColor * attenuation;
        Float3 sample = CalcLighting(normal, sampleIrradiance, sampleDir, diffuseAlbedo, position,
                                     cameraPos, roughness, includeSpecular, specAlbedo);
        result = sample * invPDF;
        areaLightIrradiance = sampleIrradiance * invPDF;
    }

    irradiance += areaLightIrradiance;

    return result;
}

// Calculates diffuse and specular contribution from the area light, given a 2D random sample point
// representing a location on the surface of the light