Rasterizes and packs glyphs from a FontFace into a TextureContainer. More...
#include <GlyphAtlas.hpp>
Collaboration diagram for MayaFlux::Portal::Text::GlyphAtlas:Public Member Functions | |
| void | add_fallback (FontFace &face) |
| Register a fallback face, tried in order after the primary on a miss. | |
| uint32_t | ascender () const |
| Ascender in pixels for this atlas's pixel_size. | |
| uint32_t | atlas_size () const |
| Atlas texture dimension (width == height == atlas_size). | |
| void | clear_dirty () |
| Clear the dirty flag after re-uploading the atlas to GPU. | |
| FontFace & | get_face () |
| Access the backing FontFace. | |
| const FontFace & | get_face () const |
| const GlyphMetrics * | get_or_rasterize (FT_UInt glyph_index) |
| Return metrics for a glyph, rasterizing it into the atlas if needed. | |
| const GlyphMetrics * | get_or_rasterize (FT_ULong codepoint) |
| Convenience: look up by Unicode codepoint. | |
| GlyphAtlas (const GlyphAtlas &)=delete | |
| GlyphAtlas (FontFace &face, uint32_t pixel_size, uint32_t atlas_size=512) | |
| Construct an atlas for a specific face and pixel size. | |
| GlyphAtlas (GlyphAtlas &&)=delete | |
| bool | is_dirty () const |
| Returns true if at least one glyph was rasterized since the last call to clear_dirty(). | |
| uint32_t | line_height () const |
| Line advance in pixels for this atlas's pixel_size. | |
| GlyphAtlas & | operator= (const GlyphAtlas &)=delete |
| GlyphAtlas & | operator= (GlyphAtlas &&)=delete |
| uint32_t | pixel_size () const |
| Pixel size passed at construction. | |
| Kakshya::TextureContainer & | texture () |
| const Kakshya::TextureContainer & | texture () const |
| The atlas texture as a TextureContainer (R8, atlas_size x atlas_size). | |
| ~GlyphAtlas ()=default | |
Private Member Functions | |
| const GlyphMetrics * | get_or_rasterize_from (FontFace &face, FT_UInt glyph_index) |
| void | grow () |
| Double the atlas texture and re-rasterize every cached glyph into it. | |
| bool | rasterize (FontFace &face, FT_UInt glyph_index) |
Private Attributes | |
| uint32_t | m_atlas_size |
| std::unordered_map< FontFace *, std::unordered_map< FT_UInt, GlyphMetrics > > | m_cache |
| Per-face glyph cache. | |
| uint32_t | m_cursor_x { 0 } |
| uint32_t | m_cursor_y { 0 } |
| bool | m_dirty { false } |
| FontFace & | m_face |
| std::vector< FontFace * > | m_fallbacks |
| uint32_t | m_pixel_size |
| uint32_t | m_shelf_height { 0 } |
| std::unique_ptr< Kakshya::TextureContainer > | m_texture |
Detailed Description
Rasterizes and packs glyphs from a FontFace into a TextureContainer.
One atlas corresponds to one (FontFace, pixel_size) pair. The atlas texture is R8 (single-channel coverage); colour is applied in the shader.
Glyphs are rasterized on first request via get_or_rasterize() and packed into the atlas using a simple shelf packing algorithm. On shelf overflow the atlas texture doubles in size and every previously cached glyph is re-rasterized into the new texture from its owning face; rasterization never permanently refuses for lack of room.
The primary face is fixed at construction. A codepoint the primary face lacks is looked up in the fallback chain (add_fallback()), in order, and the first face reporting a glyph produces it; a codepoint absent from every face fails as before. The atlas's cache is keyed on (face, glyph_index) rather than glyph_index alone, since glyph indices are only unique within the face that assigned them: the same numeric index from two different faces names two unrelated glyphs.
Callers obtain glyph indices via FT_Get_Char_Index on the FontFace. This keeps the path open for HarfBuzz, which outputs glyph indices directly (against the primary face; HarfBuzz does not participate in fallback).
Thread safety: not thread-safe. Rasterization must occur on the thread that owns the FontFace.
Definition at line 72 of file GlyphAtlas.hpp.
The documentation for this class was generated from the following files:
