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Replace stb_truetype with FreeType for proper text outline rendering

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- Add -sUSE_FREETYPE=1 to Emscripten build flags
- Extend Font class with FT_Library, FT_Face, and FT_Stroker handles
- Rewrite FontAtlas to use FreeType with on-demand stroked glyph loading
- Text outlines now use FT_Stroker for vector-based stroking before
  rasterization, eliminating gaps at corners with thick outlines
- Use glTexSubImage2D for incremental atlas updates (major perf fix)
- Disable canvas border in shell.html per Emscripten docs (alignment fix)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
This commit is contained in:
John McCardle 2026-01-31 16:45:10 -05:00
commit 67aa413a78
5 changed files with 538 additions and 128 deletions
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34
src/platform/SDL2Renderer.h
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@ -162,7 +162,10 @@ public:
FontAtlas(const FontAtlas&) = delete;
FontAtlas& operator=(const FontAtlas&) = delete;
// Load font data
// Load font using Font's FreeType handles
bool load(const class Font* font, float fontSize);
// Legacy interface for backwards compatibility (uses global FT library)
bool load(const unsigned char* fontData, size_t dataSize, float fontSize);
// Get texture atlas
@ -176,6 +179,10 @@ public:
float width, height; // Glyph dimensions in pixels
};
// Get glyph with optional outline thickness (0 = no outline)
bool getGlyph(uint32_t codepoint, float outlineThickness, GlyphInfo& info);
// Legacy interface (no outline)
bool getGlyph(uint32_t codepoint, GlyphInfo& info) const;
// Get font metrics
@ -190,11 +197,28 @@ private:
float descent_ = 0;
float lineHeight_ = 0;
// Glyph cache - maps codepoint to glyph info
std::unordered_map<uint32_t, GlyphInfo> glyphCache_;
// FreeType handles (stored for on-demand glyph loading)
const class Font* font_ = nullptr;
// stb_truetype font info (opaque pointer to avoid header inclusion)
void* stbFontInfo_ = nullptr;
// Atlas packing state for on-demand glyph loading
static const int ATLAS_SIZE = 1024;
std::vector<unsigned char> atlasPixels_;
int atlasX_ = 1;
int atlasY_ = 1;
int atlasRowHeight_ = 0;
// Glyph cache - maps (codepoint, outlineThickness) to glyph info
// Key: (outlineThickness bits << 32) | codepoint
std::unordered_map<uint64_t, GlyphInfo> glyphCache_;
// Simple glyph cache for backwards compatibility (no outline)
std::unordered_map<uint32_t, GlyphInfo> simpleGlyphCache_;
// Helper to make cache key
static uint64_t makeKey(uint32_t codepoint, float outlineThickness);
// Load a glyph on-demand with optional stroking
bool loadGlyph(uint32_t codepoint, float outlineThickness);
};
} // namespace sf