AtmosphereVolume.cpp

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#include "graphics/AtmosphereVolume.h"
#include "graphics/FogVolume.h"
#include "graphics/VolumeDensityGraph.h"
#include "graphics/SparseVolumeTexture.h"
 
#include <algorithm>
#include <cmath>
 
#include <glm/common.hpp>
#include <glm/geometric.hpp>
 
namespace eve::graphics {
 
void AtmosphereVolume::resize(int width, int height, int depth) {
    width_ = std::max(width, 1);
    height_ = std::max(height, 1);
    depth_ = std::max(depth, 1);
    media_.assign(std::size_t(width_) * std::size_t(height_) * std::size_t(depth_), {});
    integrated_.assign(media_.size(), glm::vec4(0.f, 0.f, 0.f, 1.f));
}
 
void AtmosphereVolume::clear() {
    std::fill(media_.begin(), media_.end(), FogFroxel{});
    std::fill(integrated_.begin(), integrated_.end(), glm::vec4(0.f, 0.f, 0.f, 1.f));
}
 
void AtmosphereVolume::setDepthRange(float nearDistance, float farDistance) {
    nearDistance_ = std::max(nearDistance, 1e-3f);
    farDistance_ = std::max(farDistance, nearDistance_ + 1e-3f);
}
 
float AtmosphereVolume::sliceDistance(int z) const {
    if (depth_ <= 0) return nearDistance_;
    const float t = (float(std::clamp(z, 0, depth_ - 1)) + 0.5f) / float(depth_);
    return nearDistance_ * std::pow(farDistance_ / nearDistance_, t);
}
 
int AtmosphereVolume::sliceForDistance(float distance) const {
    if (depth_ <= 1) return 0;
    const float d = std::clamp(distance, nearDistance_, farDistance_);
    const float t = std::log(d / nearDistance_) / std::log(farDistance_ / nearDistance_);
    return std::clamp(int(std::floor(t * float(depth_))), 0, depth_ - 1);
}
 
std::size_t AtmosphereVolume::index(int x, int y, int z) const {
    x = std::clamp(x, 0, width_ - 1);
    y = std::clamp(y, 0, height_ - 1);
    z = std::clamp(z, 0, depth_ - 1);
    return (std::size_t(z) * std::size_t(height_) + std::size_t(y)) * std::size_t(width_) +
           std::size_t(x);
}
 
FogFroxel &AtmosphereVolume::at(int x, int y, int z) { return media_[index(x, y, z)]; }
const FogFroxel &AtmosphereVolume::at(int x, int y, int z) const { return media_[index(x, y, z)]; }
 
void AtmosphereVolume::injectHeightFog(float baseExtinction, const glm::vec3 &albedo,
                                       float baseHeight, float heightFalloff, float minWorldY,
                                       float maxWorldY) {
    const float sigma = std::max(baseExtinction, 0.f);
    const glm::vec3 omega = glm::clamp(albedo, glm::vec3(0.f), glm::vec3(1.f));
    const float falloff = std::max(heightFalloff, 0.f);
    for (int y = 0; y < height_; ++y) {
        const float ty = (float(y) + 0.5f) / float(height_);
        const float worldY = minWorldY + (maxWorldY - minWorldY) * ty;
        const float extinction = sigma * std::exp(-falloff * std::max(worldY - baseHeight, 0.f));
        for (int z = 0; z < depth_; ++z) {
            for (int x = 0; x < width_; ++x) {
                FogFroxel &f = at(x, y, z);
                f.extinction += extinction;
                f.scattering += omega * extinction;
            }
        }
    }
}
 
void AtmosphereVolume::injectHeightFogFrustum(float baseExtinction, const glm::vec3 &albedo,
                                               float baseHeight, float heightFalloff,
                                               float minWorldY, float maxWorldY,
                                               const glm::mat4 &invViewProj) {
    const float sigma = std::max(baseExtinction, 0.f);
    const glm::vec3 omega = glm::clamp(albedo, glm::vec3(0.f), glm::vec3(1.f));
    const float falloff = std::max(heightFalloff, 0.f);
    auto unproject = [&](float ndcX, float ndcY, float ndcZ) {
        const glm::vec4 homogeneous = invViewProj * glm::vec4(ndcX, ndcY, ndcZ, 1.f);
        return glm::vec3(homogeneous) / homogeneous.w;
    };
    for (int y = 0; y < height_; ++y) {
        const float ndcY = ((float(y) + 0.5f) / float(height_)) * 2.f - 1.f;
        for (int x = 0; x < width_; ++x) {
            const float ndcX = ((float(x) + 0.5f) / float(width_)) * 2.f - 1.f;
            const glm::vec3 nearPoint = unproject(ndcX, ndcY, 0.f);
            const glm::vec3 farPoint = unproject(ndcX, ndcY, 1.f);
            for (int z = 0; z < depth_; ++z) {
                const float depth01 = (sliceDistance(z) - nearDistance_) /
                                      (farDistance_ - nearDistance_);
                const glm::vec3 world = glm::mix(nearPoint, farPoint, depth01);
                if (world.y < minWorldY || world.y > maxWorldY) continue;
                const float extinction = sigma * std::exp(-falloff * std::max(world.y - baseHeight, 0.f));
                FogFroxel &froxel = at(x, y, z);
                froxel.extinction += extinction;
                froxel.scattering += omega * extinction;
            }
        }
    }
}
 
void AtmosphereVolume::injectLocalVolume(const FogVolume &volume, const glm::vec3 &worldMin,
                                         const glm::vec3 &worldMax) {
    for (int z = 0; z < depth_; ++z) {
        for (int y = 0; y < height_; ++y) {
            for (int x = 0; x < width_; ++x) {
                const glm::vec3 uvw((float(x) + 0.5f) / float(width_),
                                    (float(y) + 0.5f) / float(height_),
                                    (float(z) + 0.5f) / float(depth_));
                const glm::vec3 world = worldMin + (worldMax - worldMin) * uvw;
                const float signedExtinction = volume.sampleExtinction(world);
                if (std::fabs(signedExtinction) <= 1e-8f) continue;
                FogFroxel &f = at(x, y, z);
                const float previous = f.extinction;
                f.extinction = std::max(0.f, previous + signedExtinction);
                if (signedExtinction > 0.f) {
                    f.scattering += volume.getAlbedo() * signedExtinction;
                    f.emissive += volume.getEmissive() * signedExtinction;
                    f.anisotropy = volume.getAnisotropy();
                } else if (previous > 1e-6f) {
                    const float scale = f.extinction / previous;
                    f.scattering *= scale;
                    f.emissive *= scale;
                }
            }
        }
    }
}
 
void AtmosphereVolume::injectLocalVolumeFrustum(const FogVolume &volume,
                                                const glm::mat4 &invViewProj) {
    auto unproject = [&](float ndcX, float ndcY, float ndcZ) {
        glm::vec4 world = invViewProj * glm::vec4(ndcX, ndcY, ndcZ, 1.f);
        return glm::vec3(world) / world.w;
    };
    for (int y = 0; y < height_; ++y) {
        const float v = (float(y) + 0.5f) / float(height_);
        for (int x = 0; x < width_; ++x) {
            const float u = (float(x) + 0.5f) / float(width_);
            const glm::vec3 nearPoint = unproject(u * 2.f - 1.f, v * 2.f - 1.f, 0.f);
            const glm::vec3 farPoint = unproject(u * 2.f - 1.f, v * 2.f - 1.f, 1.f);
            for (int z = 0; z < depth_; ++z) {
                const float depth01 = (sliceDistance(z) - nearDistance_) /
                                      (farDistance_ - nearDistance_);
                const glm::vec3 world = glm::mix(nearPoint, farPoint, depth01);
                const float signedExtinction = volume.sampleExtinction(world);
                if (std::fabs(signedExtinction) <= 1e-8f) continue;
                FogFroxel &f = at(x, y, z);
                const float previous = f.extinction;
                f.extinction = std::max(0.f, previous + signedExtinction);
                if (signedExtinction > 0.f) {
                    f.scattering += volume.getAlbedo() * signedExtinction;
                    f.emissive += volume.getEmissive() * signedExtinction;
                    f.anisotropy = volume.getAnisotropy();
                } else if (previous > 1e-6f) {
                    const float scale = f.extinction / previous;
                    f.scattering *= scale;
                    f.emissive *= scale;
                }
            }
        }
    }
}
 
void AtmosphereVolume::injectDensityGraph(const VolumeDensityGraph &graph,
                                          const glm::vec3 &worldMin,
                                          const glm::vec3 &worldMax, float extinctionScale,
                                          const glm::vec3 &albedo, float time) {
    const glm::vec3 omega = glm::clamp(albedo, glm::vec3(0.f), glm::vec3(1.f));
    for (int z = 0; z < depth_; ++z) {
        for (int y = 0; y < height_; ++y) {
            for (int x = 0; x < width_; ++x) {
                const glm::vec3 uvw((float(x) + 0.5f) / float(width_),
                                    (float(y) + 0.5f) / float(height_),
                                    (float(z) + 0.5f) / float(depth_));
                const glm::vec3 world = worldMin + (worldMax - worldMin) * uvw;
                const float extinction = graph.evaluate(world, time) * extinctionScale;
                FogFroxel &f = at(x, y, z);
                const float previous = f.extinction;
                f.extinction = std::max(0.f, previous + extinction);
                if (extinction >= 0.f)
                    f.scattering += omega * extinction;
                else if (previous > 1e-6f)
                    f.scattering *= f.extinction / previous;
            }
        }
    }
}
 
void AtmosphereVolume::injectSparseVolume(const SparseVolumeTexture &texture,
                                          float extinctionScale) {
    for (int z = 0; z < depth_; ++z) {
        for (int y = 0; y < height_; ++y) {
            for (int x = 0; x < width_; ++x) {
                const FogFroxel source = texture.sample((float(x) + 0.5f) / float(width_),
                    (float(y) + 0.5f) / float(height_), (float(z) + 0.5f) / float(depth_));
                const float scale = std::max(extinctionScale, 0.f);
                FogFroxel &target = at(x, y, z);
                target.extinction += source.extinction * scale;
                target.scattering += source.scattering * scale;
                target.emissive += source.emissive * scale;
                target.anisotropy = source.anisotropy;
            }
        }
    }
}
 
void AtmosphereVolume::integrate(const glm::vec3 &lightColor, float phaseScale) {
    const glm::vec3 light = glm::max(lightColor, glm::vec3(0.f)) * std::max(phaseScale, 0.f);
    for (int y = 0; y < height_; ++y) {
        for (int x = 0; x < width_; ++x) {
            glm::vec3 radiance(0.f);
            float transmittance = 1.f;
            float previousDistance = nearDistance_;
            for (int z = 0; z < depth_; ++z) {
                const float distance = sliceDistance(z);
                const float stepLength = std::max(distance - previousDistance, 0.f);
                previousDistance = distance;
                const FogFroxel &f = at(x, y, z);
                const float opticalDepth = f.extinction * stepLength;
                const float stepTransmittance = std::exp(-opticalDepth);
                const float integral = f.extinction > 1e-6f
                    ? (1.f - stepTransmittance) / f.extinction
                    : stepLength;
                radiance += transmittance *
                    (f.scattering * light * f.lightVisibility + f.emissive) * integral;
                transmittance *= stepTransmittance;
                integrated_[index(x, y, z)] = glm::vec4(radiance, transmittance);
            }
        }
    }
}
 
void AtmosphereVolume::integrateLocalLights(const std::vector<VolumetricLight> &lights,
                                            const glm::vec3 &worldMin,
                                            const glm::vec3 &worldMax,
                                            const glm::vec3 &ambientLight) {
    for (int y = 0; y < height_; ++y) {
        for (int x = 0; x < width_; ++x) {
            glm::vec3 radiance(0.f);
            float transmittance = 1.f;
            float previousDistance = nearDistance_;
            for (int z = 0; z < depth_; ++z) {
                const glm::vec3 uvw((float(x) + 0.5f) / float(width_),
                                    (float(y) + 0.5f) / float(height_),
                                    (float(z) + 0.5f) / float(depth_));
                const glm::vec3 world = worldMin + (worldMax - worldMin) * uvw;
                glm::vec3 incident = glm::max(ambientLight, glm::vec3(0.f));
                for (const VolumetricLight &light : lights) {
                    if (!light.enabled || light.radius <= 0.f || light.intensity <= 0.f) continue;
                    const float d = glm::length(world - light.position);
                    if (d >= light.radius) continue;
                    const float radial = 1.f - d / light.radius;
                    incident += glm::max(light.color, glm::vec3(0.f)) * light.intensity *
                        radial * radial;
                }
                const float distance = sliceDistance(z);
                const float stepLength = std::max(distance - previousDistance, 0.f);
                previousDistance = distance;
                const FogFroxel &f = at(x, y, z);
                const float opticalDepth = f.extinction * stepLength;
                const float stepTransmittance = std::exp(-opticalDepth);
                const float integral = f.extinction > 1e-6f
                    ? (1.f - stepTransmittance) / f.extinction
                    : stepLength;
                radiance += transmittance *
                    (f.scattering * incident * f.lightVisibility + f.emissive) * integral;
                transmittance *= stepTransmittance;
                integrated_[index(x, y, z)] = glm::vec4(radiance, transmittance);
            }
        }
    }
}
 
void AtmosphereVolume::setLightVisibility(int x, int y, int z, float visibility) {
    at(x, y, z).lightVisibility = std::clamp(visibility, 0.f, 1.f);
}
 
std::size_t AtmosphereVolume::blendHistory(const AtmosphereVolume &history, float historyWeight,
                                           float rejectionThreshold) {
    if (history.width_ != width_ || history.height_ != height_ || history.depth_ != depth_)
        return integrated_.size();
    const float baseWeight = std::clamp(historyWeight, 0.f, 1.f);
    const float threshold = std::max(rejectionThreshold, 0.f);
    std::size_t rejected = 0;
    for (std::size_t i = 0; i < integrated_.size(); ++i) {
        const glm::vec4 current = integrated_[i];
        const glm::vec4 previous = history.integrated_[i];
        const float currentLuma = glm::dot(glm::vec3(current), glm::vec3(0.2126f, 0.7152f, 0.0722f));
        const float previousLuma = glm::dot(glm::vec3(previous), glm::vec3(0.2126f, 0.7152f, 0.0722f));
        const float relativeDelta = std::fabs(currentLuma - previousLuma) /
            std::max(std::max(currentLuma, previousLuma), 1e-4f);
        const bool reject = relativeDelta > threshold;
        if (reject) ++rejected;
        const float weight = reject ? 0.f : baseWeight;
        integrated_[i] = glm::mix(current, previous, weight);
    }
    return rejected;
}
 
const glm::vec4 &AtmosphereVolume::integratedAt(int x, int y, int z) const {
    return integrated_[index(x, y, z)];
}
 
glm::vec4 AtmosphereVolume::sampleIntegrated(float u, float v, float distance) const {
    if (integrated_.empty()) return glm::vec4(0.f, 0.f, 0.f, 1.f);
    const int x = std::clamp(int(u * float(width_)), 0, width_ - 1);
    const int y = std::clamp(int(v * float(height_)), 0, height_ - 1);
    return integratedAt(x, y, sliceForDistance(distance));
}
 
FogFroxel AtmosphereVolume::sampleMedia(float u, float v, float w) const {
    if (media_.empty()) return {};
    const int x = std::clamp(int(u * float(width_)), 0, width_ - 1);
    const int y = std::clamp(int(v * float(height_)), 0, height_ - 1);
    const int z = std::clamp(int(w * float(depth_)), 0, depth_ - 1);
    return at(x, y, z);
}
 
}  // namespace eve::graphics