cloudy-raytracer/shader/cloudshader.cpp

#include "cloudshader.h"


Color CloudShader::shade(const Scene &scene, const Ray &ray) const
{
    Vector3d hitPoint = ray.origin + ray.direction * ray.length; // Potentially add epsilon

    // Collect getNoise through the cloud
    float accumulatedNoise = 0.0f;
    float cloudLength = 0.0f;   // Length of cloud in ray direction

    // Get background color behind cloud and information about the clouds length
    Ray cloudRay = ray;
    cloudRay.origin = ray.origin + (ray.length + REFR_EPS) * ray.direction;
    cloudRay.length = INFINITY;
    cloudRay.primitive = nullptr;

    // Get out of cloud primitive first
    if (ray.primitive->intersect(cloudRay))
    {
        // Get length
        cloudLength = cloudRay.length;

        // Prepare ray for background color
        cloudRay.setRemainingBounces(cloudRay.getRemainingBounces() + 1);
        cloudRay.origin = cloudRay.origin + (cloudRay.length + REFR_EPS) * cloudRay.direction;
        cloudRay.length = INFINITY;
        cloudRay.primitive = nullptr;
    }
    Color background = scene.traceRay(cloudRay);

    if (cloudLength == 0.0f) return background; // No cloud or at edge

    // Get getNoise through cloud
    int const NOISE_SAMPLES = settings.densitySamples;
    float stepWeight = cloudLength / (float) NOISE_SAMPLES;
    for (int i = 0; i < NOISE_SAMPLES; ++i)
    {
        float progress = (float) i / (float) NOISE_SAMPLES;
        Vector3d samplePoint = hitPoint + progress * cloudLength * ray.direction;
        float sampleDensity = getCloudDensity(samplePoint);
        accumulatedNoise += sampleDensity * stepWeight;
    }

    // Pre-processs accumulated getNoise
//    accumulatedNoise /= (float) NOISE_SAMPLES;
    float cloudDensity = exp(-accumulatedNoise * settings.densityAbsorption);

    return background * cloudDensity;

    if (accumulatedNoise < 1 - settings.densityTreshold)
    {
        accumulatedNoise = 0;
    } else
    {
        // Fade out the getNoise
        accumulatedNoise = (accumulatedNoise - (1 - settings.densityTreshold)) / settings.densityTreshold;
    }
//    return accumulatedNoise * Color(1, 1, 1);

    // Use the getNoise to control the densityTreshold of the clouds
    Color cloud = background * (1.0f - accumulatedNoise) + settings.cloudColor * accumulatedNoise;

    // Use the getNoise to add some wispy details to the clouds
    cloud += settings.wispyColor * (accumulatedNoise * settings.wispyIntensity);

    // Add some ambient and diffuse lighting
//    cloud += scene.ambientLight() * material.ambient();
//    for (const auto &light: scene.lights())
//    {
//        Light::Illumination illumination = light->illuminate(scene, ray);
//        if (illumination.distance == 0.0f) continue; // Skip ambient light
//        float diffuse = dotProduct(normal, illumination.direction);
//        cloud += material.cloud() * illumination.cloud * diffuse;
//    }
    return cloud;
}

bool CloudShader::isTransparent() const
{
    return true;
}

CloudShader::CloudShader(const CloudSettings &settings) : settings(settings),
                                                          noise(WorleyNoise(
                                                                  NOISE_SIZE,
                                                                  NOISE_POINTS)
                                                          )
{
    noise.invert = true;
}

float CloudShader::getCloudDensity(Vector3d point) const
{
    point /= settings.scale;

    // Get corner points of the cube
    int x_min = (int) fitToNoise(floor(point.x));
    int y_min = (int) fitToNoise(floor(point.y));
    int z_min = (int) fitToNoise(floor(point.z));

    int x_max = fitToNoise(x_min + 1);
    int y_max = fitToNoise(y_min + 1);
    int z_max = fitToNoise(z_min + 1);

    // Get the getNoise values at the corner points
    float n000 = noise.getNoise(x_min, y_min, z_min);
    float n001 = noise.getNoise(x_min, y_min, z_max);
    float n010 = noise.getNoise(x_min, y_max, z_min);
    float n011 = noise.getNoise(x_min, y_max, z_max);
    float n100 = noise.getNoise(x_max, y_min, z_min);
    float n101 = noise.getNoise(x_max, y_min, z_max);
    float n110 = noise.getNoise(x_max, y_max, z_min);
    float n111 = noise.getNoise(x_max, y_max, z_max);

    // Get fractions
    float fx = point.x - floor(point.x);
    float fy = point.y - floor(point.y);
    float fz = point.z - floor(point.z);

    // Interpolate
    float nx00 = n000 * (1 - fx) + n100 * fx;
    float nx01 = n001 * (1 - fx) + n101 * fx;
    float nx10 = n010 * (1 - fx) + n110 * fx;
    float nx11 = n011 * (1 - fx) + n111 * fx;

    float nxy0 = nx00 * (1 - fy) + nx10 * fy;
    float nxy1 = nx01 * (1 - fy) + nx11 * fy;

    float density = nxy0 * (1 - fz) + nxy1 * fz;

    // Treshold
    density = std::max(0.0f, density - settings.densityTreshold) * settings.densityIntensity;

    return density;
}

float CloudShader::fitToNoise(float point) const
{
    float remainingValue = fmod(point, NOISE_SIZE);

    if (remainingValue < 0)
    {
        remainingValue += NOISE_SIZE;
    }

    return remainingValue;
}