The coverage threshold (0.5 in fbd4e5ad1, lowered to 0.3 in d4106ef2d to
get CI green) is environment-dependent: a correctly sized emoji covers
~0.84 of its cell on one box but ~0.39 in CI, while the buggy render is
~0.28, so the margin is thin and font/cell dependent.
Render the same font two ways at one size instead: via its fontconfig
descriptor (which carries the size-fixup matrix) and via its file path
(which does not). They must come out the same size; the bug shrinks the
descriptor one. Only the matrix differs, so the check no longer depends
on the environment or the emoji artwork.
ee937bdd1b routed FC_MATRIX through the cairo font matrix so synthetic
slant reaches color glyphs. But FC_MATRIX is also how fontconfig encodes
the pixel-size fixup of fixed-size faces. Noto Color Emoji is a ~109px
bitmap strike and fontconfig hands consumers a matrix scaling it to the
requested size (factor = requested_px / strike_px). cairo_set_font_size()
already brings the strike to the requested size, so feeding that matrix
into cairo_set_font_matrix() in apply_cairo_font_size() scales it down
again by the fixup factor. At terminal cell sizes that is a large shrink,
up to ~9x for small cells (easing to 1x as the cell nears the strike), so
color emoji render as a dot; fit_cairo_glyph() only shrinks, so it never
grows them back.
Only the shear carries synthetic slant; the diagonal is the size, which
cairo_set_font_size() and fit_cairo_glyph() already handle. Apply only
the shear and fall through to cairo_set_font_size() when there is no
shear. Pure-slant matrices are unchanged. This carries only the shear to
color glyphs, so a non-uniform diagonal scale from a hand-built FC_MATRIX
is dropped on that path; the stock fixup is uniform, so dropping it is
the intended behaviour.
Add a regression test that renders a color emoji and checks it fills its
cells, skipped unless a fixed-size color font with a fontconfig fixup
matrix is present.
Fixes#10144
fontconfig's FcFontList omits FC_MATRIX from its object set
(kitty/fontconfig.c), so a roman font that find_best_match finds there
(e.g. Fira Code, which ships no italic, in both its static and variable
builds) carries no synthetic-italic shear and its "italic" renders upright.
A family that is not found is substituted, and when the substitute
resolves through the listed faces those descriptors are equally
matrix-less, so this attach covers them too. Only raw fc_match
descriptors (runtime glyph-fallback faces via create_fallback_face, and
find_best_match's last-resort return) already carry the matrix from
substitution.
The italic intent for the configured faces exists only during selection,
not at face construction, so attach the matrix at the end of
get_font_files: for an italic slot whose chosen face is upright and has no
matrix, ask fc_match what fontconfig would do. fc_match returns a synthetic
matrix only when there is no real italic to use (no italic face and no
slanted named instance or variable slant axis), so a font that is already
italic, static or variable, is never double-slanted. Face construction
applies the matrix via FT_Set_Transform; the previous commit makes it
survive the size specialization step the render path builds faces from.
Only the matrix is taken, so selection is unchanged.
FontConfigPattern declared matrix as a required key, but pattern_as_dict
sets it only when the pattern has one, so declare it NotRequired. With
that and narrowing on descriptor_type the attach needs no cast.
Add a regression test (test_synthetic_italic_matrix): a roman no-italic
font gets a non-identity matrix on its italic slot while a real-italic
control does not, and the matrix survives specialize_font_descriptor. It
asserts the invariant rather than the exact shear (the value is
fontconfig's, version-dependent) and skips when the synthetic rule is
inactive.
Covers the four configured faces. Limitation: fc_match re-matches by family
name, so under an uncommon config (a multi-face family key plus a user
per-font FC_MATRIX rule keyed on width/style) it can attach a matrix
computed for a different face; the 90-synthetic shear this targets is
weight-independent and unaffected. A production version should re-match the
selected face by path+index+slant.
Store in a separate VAO instead more performant as it uses less VRAM and
allows shader lookup co-ords to be passed to fragment shaders without
calculation in the fragment shader.
Will allow sprites to point to where their decorations should be read
from, for instance. Needed for scaled text and also if we want to
implement decoration avoidance.
Frees up two bytes in GPUCell. Doesn't require a minimum texture row
size. Makes a bunch of code faster. Index uses 31 bits which gives us
2,147,483,647 aka ~ 2 billion sprites.
