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FreeType and HarfBuzz allocated with libc malloc, out of sight of the Zig
allocator the rest of the gui uses, so its Debug leak report and a test's
std.testing.allocator never saw them. Now every allocation the font code
makes goes through ui_malloc, ui_calloc, ui_realloc and ui_free, exported
from gui.zig over `font_allocator`:
- HarfBuzz is compiled with hb_malloc_impl and friends pointing at them.
- Each UIFont gives its FreeType library its own memory manager
(FT_New_Library with an FT_MemoryRec_ over the same functions, then
FT_Add_Default_Modules and FT_Set_Default_Properties: exactly what
FT_Init_FreeType does over its malloc manager), torn down with
FT_Done_Library.
- The shim's own UIFont and scratch arrays use them too.
C's free and realloc pass no size, so a block starts with a 32-byte header
(the caller's pointer stays 16-byte, max_align_t, aligned) holding its size
and the allocator that made it, so a block goes back where it came from
even after font_allocator is repointed. runNative points font_allocator at
the gui's gpa. HarfBuzz makes a few process-wide objects on first use and
never frees them (the default Unicode functions, the locale's language,
hb-ft's font functions); ui_font_prime makes them from the default heap
before that, so a Debug build's leak report stays about fonts. Tests do the
same: the shaping tests, and a new test that creates, rasterizes and shapes
fonts under std.testing.allocator, report any leak. Only the render thread
calls into fonts, and every allocator used is thread-safe.
It costs nothing measurable: against the previous change, 10 interleaved
rounds with an A/A pair show every scenario as fast or faster with Adwaita
Mono and Maple Mono alike, and first paint over 30 launches each matches
main.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
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their cells
The SDL shell rasterized every cell by its own codepoint, so a font's `->`,
`!=` or `<=` ligature never appeared. Text is now shaped with HarfBuzz 11.0.0,
built from source like FreeType: a lazy build.zig.zon dependency (the tarball
Ghostty pins) compiled only for the gui shell, its FreeType integration
linked against the freetype package, so the binary carries no system
HarfBuzz or FreeType and a tty build never compiles it.
Shaping turns on only the font's ligature features (liga, calt, clig, rlig,
rclt); composition, local forms and fractions stay off, so a cell draws either
its nominal glyph, as it always did, or part of a ligature. A glyph no lookup
of those features covers cannot change, so its cell is resolved alone, and
that resolution is cached by codepoint: in a font without ligatures (Adwaita
Mono) no cell is ever shaped, and the pipeline draws pixel for pixel as
before.
A cell whose glyph a ligature could replace is shaped with its word: the
cells between spaces that share a decoration and a role. A word ends either
side of the cursor, block or bar, so the cell being edited shows its own
character (Ghostty's rule), and inside f|i, f|l and s|t, whose typographic
ligatures do not belong on a grid (Ghostty again). Colours never end a word:
a ligature spans a syntax colour change or a selection edge. A codepoint the
primary font lacks shapes in the fallback face that has it. Taglines are not
shaped: they are drawn at two pitches, and a strip would not line up in one.
HarfBuzz only chooses glyphs; the grid places them. A substituted glyph whose
ink reaches over neighbouring cells that draw nothing of their own (the
spacer glyphs of Fira Code-style fonts such as Maple Mono, or the cells a
merged ligature cluster swallowed) claims them: it is rasterized once as a
strip that many cells wide, and each cell samples its own slice, so
selection, the cursor and per-cell colours work unchanged. Anything the grid
cannot place (several glyphs in one cell, a positioned mark) keeps its
nominal glyphs.
A frame must not pay for this. A shaped word's atlas slots are cached by its
text (checked against the stored text, not just its hash), so a frame costs
one lookup per word and a compare for the rest of the word being walked.
The atlas is keyed by (face, glyph, role, decoration, lead, span), packed into
64 bits so a lookup hashes one word; ASCII glyph ids are a table, and a
face's HarfBuzz state is made when it is first asked about a glyph. Measured
with the latency trace, whose F line now also carries the submit time (CPU =
submit - present entry), in 10 interleaved rounds against main with an A/A
pair, at 160x50 cells: with Adwaita Mono every scenario (idle, scrolling,
typing, terminal output) is as fast or 1-3% faster, and the first frame and
time to first paint are unchanged. With Maple Mono, ligatures cost the first
frame about 0.8 ms (HarfBuzz setup and shaping the screen) and scrolling new
text about 1-2%.
With it the codepoint raster path is gone: grips look up their glyph and
stay centered, since a grip is not text. ui_font_scale_for_height, an
identity kept as a "size token", is removed (px is the size everywhere),
ui_font_has_glyph becomes ui_font_glyph, and the space slot is simply the
first, cleared cell of the atlas rather than a rasterized space. CellStyle.ul
gets an explicit u3 tag so a decoration fits in the packed keys.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
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stb_truetype sources
Bold in the SDL shell was a smear of the finished glyph: every pixel took
the larger of itself and three quarters of its left neighbour. That added a
grey fringe on the right of each stem instead of a thicker stem, so bold read
as blurred regular text, and at large sizes it barely read as bold at all.
The rasterizer now does what Ghostty's FreeType face does: it loads the
hinted glyph, thickens the outline with FT_Outline_Embolden, and renders
that. The stems widen as one shape with hinted edges, and the advance is
untouched, so the cell grid, caret and selection do not move. The strength
is Ghostty's heuristic, 1/32 of the line height rounded up (one pixel at a
32 px line). A bitmap strike has no outline; it is widened by one whole
pixel with FT_Bitmap_Embolden, the classic overstrike. Underline and
strikethrough are still drawn into the cached cell mask (decorateLine).
vendor/stb (stb_truetype.h and its implementation unit) was left over from
the rasterizer FreeType replaced; nothing built or referenced it.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
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