add glyph atlas class

include/llmr/geometry/glyph_atlas.hpp

@@ -0,0 +1,53 @@
+#ifndef LLMR_GEOMETRY_GLYPH_ATLAS
+#define LLMR_GEOMETRY_GLYPH_ATLAS
+
+#include <llmr/geometry/binpack.hpp>
+
+#include <string>
+#include <set>
+#include <map>
+
+namespace llmr {
+
+class Glyph {
+public:
+    uint32_t id = 0;
+    std::string bitmap;
+    uint16_t width = 0;
+    uint16_t height = 0;
+};
+
+class GlyphAtlas {
+public:
+
+private:
+    struct GlyphValue {
+        GlyphValue(const Rect<uint16_t>& rect, uint64_t id)
+            : rect(rect), ids({ id }) {}
+        Rect<uint16_t> rect;
+        std::set<uint64_t> ids;
+    };
+
+public:
+    GlyphAtlas(uint16_t width, uint16_t height);
+    ~GlyphAtlas();
+
+
+    Rect<uint16_t> addGlyph(uint64_t tile_id, const std::string& face_name,
+                            const Glyph& glyph, uint8_t buffer);
+    void removeGlyphs(uint64_t tile_id);
+    void bind();
+
+private:
+    const uint16_t width = 0;
+    const uint16_t height = 0;
+    BinPack<uint16_t> bin;
+    std::map<std::string, std::map<uint32_t, GlyphValue>> index;
+    char *const data = NULL;
+    bool dirty = true;
+    uint32_t texture = 0;
+};
+
+};
+
+#endif

src/geometry/glyph_atlas.cpp

@@ -0,0 +1,130 @@
+#include <llmr/geometry/glyph_atlas.hpp>
+#include <llmr/platform/gl.hpp>
+
+#include <cassert>
+#include <algorithm>
+
+
+using namespace llmr;
+
+GlyphAtlas::GlyphAtlas(uint16_t width, uint16_t height)
+    : width(width),
+      height(height),
+      bin(width, height),
+      data(new char[width *height]) {
+}
+
+GlyphAtlas::~GlyphAtlas() {
+    delete[] data;
+}
+
+Rect<uint16_t> GlyphAtlas::addGlyph(uint64_t tile_id, const std::string& face_name,
+                                    const Glyph& glyph, uint8_t buffer) {
+
+    std::map<uint32_t, GlyphValue>& face = index[face_name];
+    std::map<uint32_t, GlyphValue>::iterator it = face.find(glyph.id);
+
+    // The glyph is already in this texture.
+    if (it != face.end()) {
+        GlyphValue& value = it->second;
+        value.ids.insert(tile_id);
+        return value.rect;
+    }
+
+    // The glyph bitmap has zero width.
+    if (!glyph.width) {
+        return { 0, 0, 0, 0 };
+    }
+
+    uint16_t buffered_width = glyph.width + buffer * 2;
+    uint16_t buffered_height = glyph.height + buffer * 2;
+
+    // Add a 1px border around every image.
+    uint16_t pack_width = buffered_width;
+    uint16_t pack_height = buffered_height;
+
+    // Increase to next number divisible by 4, but at least 1.
+    // This is so we can scale down the texture coordinates and pack them
+    // into 2 bytes rather than 4 bytes.
+    pack_width += (4 - pack_width % 4);
+    pack_height += (4 - pack_height % 4);
+
+    Rect<uint16_t> rect = bin.allocate(pack_width, pack_height);
+    if (rect.w == 0) {
+        fprintf(stderr, "glyph bitmap overflow");
+        return rect;
+    }
+
+    assert(rect.x + rect.w <= width);
+    assert(rect.y + rect.h <= height);
+
+    face.emplace(glyph.id, GlyphValue { rect, tile_id });
+
+    // Copy the bitmap
+    char *target = data;
+    const char *source = glyph.bitmap.data();
+    for (uint32_t y = 0; y < buffered_height; y++) {
+        uint32_t y1 = width * (rect.y + y) + rect.x;
+        uint32_t y2 = buffered_width * y;
+        for (uint32_t x = 0; x < buffered_width; x++) {
+            target[y1 + x] = source[y2 + x];
+        }
+    }
+
+    dirty = true;
+
+    return rect;
+}
+
+void GlyphAtlas::removeGlyphs(uint64_t tile_id) {
+    for (auto& faces : index) {
+        std::map<uint32_t, GlyphValue>& face = faces.second;
+        for (auto it = face.begin(); it != face.end(); /* we advance in the body */) {
+            GlyphValue& value = it->second;
+            value.ids.erase(tile_id);
+
+            if (!value.ids.size()) {
+                const Rect<uint16_t>& rect = value.rect;
+
+                // Clear out the bitmap.
+                char *target = data;
+                for (uint32_t y = 0; y < rect.h; y++) {
+                    uint32_t y1 = width * (rect.y + y) + rect.x;
+                    for (uint32_t x = 0; x < rect.w; x++) {
+                        target[y1 + x] = 0;
+                    }
+                }
+
+                dirty = true;
+
+                bin.release(rect);
+
+                // Make sure to post-increment the iterator: This will return the
+                // current iterator, but will go to the next position before we
+                // erase the element from the map. That way, the iterator stays
+                // valid.
+                face.erase(it++);
+            } else {
+                ++it;
+            }
+        }
+    }
+}
+
+void GlyphAtlas::bind() {
+    if (!texture) {
+        glGenTextures(1, &texture);
+        glBindTexture(GL_TEXTURE_2D, texture);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+    } else {
+        glBindTexture(GL_TEXTURE_2D, texture);
+    }
+
+    if (dirty) {
+        glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, width, height, 0, GL_ALPHA, GL_UNSIGNED_BYTE, data);
+        dirty = false;
+    }
+};