1 files changed, 183 insertions, 0 deletions
diff --git a/src/game/client/voxel_atlas.cc b/src/game/client/voxel_atlas.cc
new file mode 100644
index 0000000..ef996e2
--- /dev/null
+++ b/src/game/client/voxel_atlas.cc
@@ -0,0 +1,183 @@
+#include "client/pch.hh"
+
+#include "client/voxel_atlas.hh"
+
+#include "core/constexpr.hh"
+#include "core/crc64.hh"
+#include "core/image.hh"
+#include "core/resource.hh"
+
+struct AtlasPlane final {
+    std::unordered_map<std::size_t, std::size_t> lookup;
+    std::vector<AtlasStrip> strips;
+    std::size_t layer_count_max;
+    std::size_t layer_count;
+    std::size_t plane_id;
+    GLuint gl_texture;
+};
+
+static int atlas_width;
+static int atlas_height;
+static std::size_t atlas_count;
+static std::vector<AtlasPlane> planes;
+
+// Certain animated and varied voxels just double their
+// textures (see the "default" texture part in VoxelInfoBuilder::build)
+// so there could either be six UNIQUE atlas strips or only one
+// https://crypto.stackexchange.com/questions/55162/best-way-to-hash-two-values-into-one
+static std::size_t vector_hash(const std::vector<std::string>& strings)
+{
+    std::size_t source = 0;
+    for(const std::string& str : strings)
+        source += crc64::get(str);
+    return crc64::get(&source, sizeof(source));
+}
+
+static void plane_setup(AtlasPlane& plane)
+{
+    glGenTextures(1, &plane.gl_texture);
+    glBindTexture(GL_TEXTURE_2D_ARRAY, plane.gl_texture);
+    glTexImage3D(GL_TEXTURE_2D_ARRAY, 0, GL_RGBA8, atlas_width, atlas_height, plane.layer_count_max, 0, GL_RED, GL_UNSIGNED_BYTE, nullptr);
+    glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_LINEAR);
+    glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_S, GL_REPEAT);
+    glTexParameteri(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_T, GL_REPEAT);
+}
+
+static AtlasStrip* plane_lookup(AtlasPlane& plane, std::size_t hash_value)
+{
+    const auto it = plane.lookup.find(hash_value);
+
+    if(it != plane.lookup.cend()) {
+        return &plane.strips[it->second];
+    }
+
+    return nullptr;
+}
+
+static AtlasStrip* plane_new_strip(AtlasPlane& plane, const std::vector<std::string>& paths, std::size_t hash_value)
+{
+    AtlasStrip strip = {};
+    strip.offset = plane.layer_count;
+    strip.plane = plane.plane_id;
+
+    glBindTexture(GL_TEXTURE_2D_ARRAY, plane.gl_texture);
+
+    for(std::size_t i = 0; i < paths.size(); ++i) {
+        if(auto image = resource::load<Image>(paths[i].c_str(), IMAGE_LOAD_FLIP)) {
+            if((image->size.x != atlas_width) || (image->size.y != atlas_height)) {
+                spdlog::warn("atlas: {}: size mismatch", paths[i]);
+                continue;
+            }
+
+            const std::size_t offset = strip.offset + i;
+            glTexSubImage3D(
+                GL_TEXTURE_2D_ARRAY, 0, 0, 0, offset, image->size.x, image->size.y, 1, GL_RGBA, GL_UNSIGNED_BYTE, image->pixels);
+        }
+    }
+
+    plane.layer_count += paths.size();
+
+    const std::size_t index = plane.strips.size();
+    plane.lookup.emplace(hash_value, index);
+    plane.strips.push_back(std::move(strip));
+    return &plane.strips[index];
+}
+
+void voxel_atlas::create(int width, int height, std::size_t count)
+{
+    GLint max_plane_layers;
+
+    atlas_width = 1 << vx::log2(width);
+    atlas_height = 1 << vx::log2(height);
+
+    // Clipping this at OpenGL 4.5 limit of 2048 is important due to
+    // how voxel quad meshes are packed in memory: each texture index is
+    // confined in 11 bits so having bigger atlas planes makes no sense;
+    glGetIntegerv(GL_MAX_ARRAY_TEXTURE_LAYERS, &max_plane_layers);
+    max_plane_layers = vx::clamp(max_plane_layers, 256, 2048);
+
+    for(long i = count; i > 0L; i -= max_plane_layers) {
+        AtlasPlane plane = {};
+        plane.plane_id = planes.size();
+        plane.layer_count_max = vx::min<std::size_t>(max_plane_layers, i);
+        plane.layer_count = 0;
+
+        const std::size_t save_id = plane.plane_id;
+        planes.push_back(std::move(plane));
+        plane_setup(planes[save_id]);
+    }
+
+    spdlog::debug("voxel_atlas: count={}", count);
+    spdlog::debug("voxel_atlas: atlas_size=[{}x{}]", atlas_width, atlas_height);
+    spdlog::debug("voxel_atlas: max_plane_layers={}", max_plane_layers);
+}
+
+void voxel_atlas::destroy(void)
+{
+    for(const AtlasPlane& plane : planes)
+        glDeleteTextures(1, &plane.gl_texture);
+    atlas_width = 0;
+    atlas_height = 0;
+    planes.clear();
+}
+
+std::size_t voxel_atlas::plane_count(void)
+{
+    return planes.size();
+}
+
+GLuint voxel_atlas::plane_texture(std::size_t plane_id)
+{
+    if(plane_id < planes.size()) {
+        return planes[plane_id].gl_texture;
+    } else {
+        return 0;
+    }
+}
+
+void voxel_atlas::generate_mipmaps(void)
+{
+    for(const AtlasPlane& plane : planes) {
+        glBindTexture(GL_TEXTURE_2D_ARRAY, plane.gl_texture);
+        glGenerateMipmap(GL_TEXTURE_2D_ARRAY);
+    }
+}
+
+AtlasStrip* voxel_atlas::find_or_load(const std::vector<std::string>& paths)
+{
+    const std::size_t hash_value = vector_hash(paths);
+
+    for(AtlasPlane& plane : planes) {
+        if(AtlasStrip* strip = plane_lookup(plane, hash_value)) {
+            return strip;
+        }
+
+        continue;
+    }
+
+    for(AtlasPlane& plane : planes) {
+        if((plane.layer_count + paths.size()) <= plane.layer_count_max) {
+            return plane_new_strip(plane, paths, hash_value);
+        }
+
+        continue;
+    }
+
+    return nullptr;
+}
+
+AtlasStrip* voxel_atlas::find(const std::vector<std::string>& paths)
+{
+    const std::size_t hash_value = vector_hash(paths);
+
+    for(AtlasPlane& plane : planes) {
+        if(AtlasStrip* strip = plane_lookup(plane, hash_value)) {
+            return strip;
+        }
+
+        continue;
+    }
+
+    return nullptr;
+}