SparseVolumeTexture.cpp

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#include "graphics/SparseVolumeTexture.h"
 
#include "graphics/VolumeDensityGraph.h"
 
#include <algorithm>
#include <cmath>
#include <fstream>
 
#include <glm/common.hpp>
 
namespace eve::graphics {
namespace {
 
constexpr char kMagic[4] = {'E', 'V', 'S', 'V'};
constexpr std::uint32_t kVersion = 1;
 
template <typename T>
bool writeValue(std::ofstream &stream, const T &value) {
    stream.write(reinterpret_cast<const char *>(&value), sizeof(T));
    return bool(stream);
}
 
template <typename T>
bool readValue(std::ifstream &stream, T &value) {
    stream.read(reinterpret_cast<char *>(&value), sizeof(T));
    return bool(stream);
}
 
bool isVacuum(const FogFroxel &f) {
    return f.extinction == 0.f && f.scattering == glm::vec3(0.f) && f.emissive == glm::vec3(0.f);
}
 
}  // namespace
 
void SparseVolumeTexture::resize(int width, int height, int depth, int brickSize) {
    width_ = std::max(width, 1);
    height_ = std::max(height, 1);
    depth_ = std::max(depth, 1);
    brickSize_ = std::clamp(brickSize, 2, 32);
    bricks_.clear();
}
 
void SparseVolumeTexture::clear() { bricks_.clear(); }
 
std::size_t SparseVolumeTexture::getAllocatedVoxelCount() const {
    const std::size_t perBrick = std::size_t(brickSize_) * std::size_t(brickSize_) *
        std::size_t(brickSize_);
    return bricks_.size() * perBrick;
}
 
bool SparseVolumeTexture::inBounds(int x, int y, int z) const {
    return x >= 0 && y >= 0 && z >= 0 && x < width_ && y < height_ && z < depth_;
}
 
std::uint64_t SparseVolumeTexture::brickKey(int bx, int by, int bz) const {
    return (std::uint64_t(std::uint32_t(bx)) << 42) |
        (std::uint64_t(std::uint32_t(by)) << 21) | std::uint64_t(std::uint32_t(bz));
}
 
std::size_t SparseVolumeTexture::localIndex(int x, int y, int z) const {
    const int lx = x % brickSize_;
    const int ly = y % brickSize_;
    const int lz = z % brickSize_;
    return (std::size_t(lz) * std::size_t(brickSize_) + std::size_t(ly)) *
        std::size_t(brickSize_) + std::size_t(lx);
}
 
void SparseVolumeTexture::setVoxel(int x, int y, int z, const FogFroxel &voxel) {
    if (!inBounds(x, y, z)) return;
    const std::uint64_t key = brickKey(x / brickSize_, y / brickSize_, z / brickSize_);
    auto found = bricks_.find(key);
    if (found == bricks_.end()) {
        if (isVacuum(voxel)) return;
        Brick brick;
        brick.voxels.resize(std::size_t(brickSize_) * std::size_t(brickSize_) *
                            std::size_t(brickSize_));
        found = bricks_.emplace(key, std::move(brick)).first;
    }
    found->second.voxels[localIndex(x, y, z)] = voxel;
}
 
FogFroxel SparseVolumeTexture::getVoxel(int x, int y, int z) const {
    if (!inBounds(x, y, z)) return {};
    const auto found = bricks_.find(brickKey(x / brickSize_, y / brickSize_, z / brickSize_));
    return found == bricks_.end() ? FogFroxel{} : found->second.voxels[localIndex(x, y, z)];
}
 
FogFroxel SparseVolumeTexture::sample(float u, float v, float w) const {
    return getVoxel(std::clamp(int(u * float(width_)), 0, width_ - 1),
                    std::clamp(int(v * float(height_)), 0, height_ - 1),
                    std::clamp(int(w * float(depth_)), 0, depth_ - 1));
}
 
void SparseVolumeTexture::bake(const VolumeDensityGraph &graph, const glm::vec3 &worldMin,
                               const glm::vec3 &worldMax, float extinctionScale,
                               const glm::vec3 &albedo, float emptyThreshold, float time) {
    clear();
    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 float extinction = std::max(0.f, graph.evaluate(
                    worldMin + (worldMax - worldMin) * uvw, time) * extinctionScale);
                if (extinction <= emptyThreshold) continue;
                FogFroxel voxel;
                voxel.extinction = extinction;
                voxel.scattering = omega * extinction;
                setVoxel(x, y, z, voxel);
            }
        }
    }
}
 
bool SparseVolumeTexture::save(const std::string &path) const {
    std::ofstream stream(path, std::ios::binary | std::ios::trunc);
    if (!stream) return false;
    stream.write(kMagic, sizeof(kMagic));
    const std::uint32_t width = std::uint32_t(width_), height = std::uint32_t(height_);
    const std::uint32_t depth = std::uint32_t(depth_), brickSize = std::uint32_t(brickSize_);
    const std::uint64_t brickCount = std::uint64_t(bricks_.size());
    if (!writeValue(stream, kVersion) || !writeValue(stream, width) || !writeValue(stream, height) ||
        !writeValue(stream, depth) || !writeValue(stream, brickSize) ||
        !writeValue(stream, brickCount)) return false;
    std::vector<std::uint64_t> keys;
    keys.reserve(bricks_.size());
    for (const auto &entry : bricks_) keys.push_back(entry.first);
    std::sort(keys.begin(), keys.end());
    for (std::uint64_t key : keys) {
        if (!writeValue(stream, key)) return false;
        const Brick &brick = bricks_.at(key);
        for (const FogFroxel &f : brick.voxels) {
            const float values[9] = {f.scattering.x, f.scattering.y, f.scattering.z, f.extinction,
                                     f.emissive.x, f.emissive.y, f.emissive.z, f.anisotropy,
                                     f.lightVisibility};
            stream.write(reinterpret_cast<const char *>(values), sizeof(values));
            if (!stream) return false;
        }
    }
    return true;
}
 
bool SparseVolumeTexture::load(const std::string &path) {
    std::ifstream stream(path, std::ios::binary);
    char magic[4]{};
    stream.read(magic, sizeof(magic));
    std::uint32_t version = 0, width = 0, height = 0, depth = 0, brickSize = 0;
    std::uint64_t brickCount = 0;
    if (!stream || !std::equal(std::begin(magic), std::end(magic), std::begin(kMagic)) ||
        !readValue(stream, version) || version != kVersion || !readValue(stream, width) ||
        !readValue(stream, height) || !readValue(stream, depth) || !readValue(stream, brickSize) ||
        !readValue(stream, brickCount) || width == 0 || height == 0 || depth == 0 ||
        brickSize < 2 || brickSize > 32) return false;
    SparseVolumeTexture loaded;
    loaded.resize(int(width), int(height), int(depth), int(brickSize));
    const std::size_t voxelsPerBrick = std::size_t(brickSize) * std::size_t(brickSize) *
        std::size_t(brickSize);
    for (std::uint64_t i = 0; i < brickCount; ++i) {
        std::uint64_t key = 0;
        if (!readValue(stream, key)) return false;
        Brick brick;
        brick.voxels.resize(voxelsPerBrick);
        for (FogFroxel &f : brick.voxels) {
            float values[9]{};
            stream.read(reinterpret_cast<char *>(values), sizeof(values));
            if (!stream) return false;
            f.scattering = {values[0], values[1], values[2]};
            f.extinction = values[3];
            f.emissive = {values[4], values[5], values[6]};
            f.anisotropy = values[7];
            f.lightVisibility = values[8];
        }
        loaded.bricks_.emplace(key, std::move(brick));
    }
    *this = std::move(loaded);
    return true;
}
 
}  // namespace eve::graphics