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macOS: Fix rendering of the unicode hyphen (U+2010) character when using a font that does not include a glyph for it

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The problem was caused by CoreText falling back to the glyph for the
ASCII hyphen U+00AD when the font does not contain a glyph for U+2010.
However, HarfBuzz does not do this automatic fallback (see
https://github.com/harfbuzz/harfbuzz/issues/517). This leads to the
character not being rendered.

To fix this we specialize HarfBuzz glyph lookup for this character
to follow CoreText. HarfBuzz should really do this automatically when
the hb_font is based on a CTFontRef, but I dont have the time/energy to
argue with its maintainers. Note that HarfBuzz already does this
automatic fallback for U+2011.

Hopefully, there aren't many more such special cases in CoreText.

Fixes #7525
This commit is contained in:
Kovid Goyal
2024-06-29 14:22:04 +05:30
parent ab296b1551
commit 78d1275601
2 changed files with 46 additions and 4 deletions
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48
kitty/core_text.m
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@@ -512,16 +512,56 @@ set_size(CTFace *self, PyObject *args) {
Py_RETURN_NONE;
}
// CoreText delegates U+2010 to U+00AD if the font is missing U+2010. Example
// of such a font is Fira Code. So we specialize HarfBuzz glyph lookup to take
// this into account.
static hb_bool_t
get_nominal_glyph(hb_font_t *font, void *font_data, hb_codepoint_t unicode, hb_codepoint_t *glyph, void *user_data) {
hb_font_t *parent_font = font_data; (void)user_data; (void)font;
hb_bool_t ans = hb_font_get_nominal_glyph(parent_font, unicode, glyph);
if (!ans && unicode == 0x2010) {
CTFontRef ct_font = hb_coretext_font_get_ct_font(parent_font);
unsigned int gid = glyph_id_for_codepoint_ctfont(ct_font, unicode);
if (gid > 0) {
ans = true; *glyph = gid;
}
}
return ans;
}
static hb_bool_t
get_variation_glyph(hb_font_t *font, void *font_data, hb_codepoint_t unicode, hb_codepoint_t variation, hb_codepoint_t *glyph, void *user_data) {
hb_font_t *parent_font = font_data; (void)user_data; (void)font;
hb_bool_t ans = hb_font_get_variation_glyph(parent_font, unicode, variation, glyph);
if (!ans && unicode == 0x2010) {
CTFontRef ct_font = hb_coretext_font_get_ct_font(parent_font);
unsigned int gid = glyph_id_for_codepoint_ctfont(ct_font, unicode);
if (gid > 0) {
ans = true; *glyph = gid;
}
}
return ans;
}
hb_font_t*
harfbuzz_font_for_face(PyObject* s) {
CTFace *self = (CTFace*)s;
if (!self->hb_font) {
self->hb_font = hb_coretext_font_create(self->ct_font);
if (!self->hb_font) fatal("Failed to create hb_font");
hb_font_t *hb = hb_coretext_font_create(self->ct_font);
if (!hb) fatal("Failed to create hb_font_t");
// dunno if we need this, harfbuzz docs say it is used by CoreText
// for optical sizing which changes the look of glyphs at small and large sizes
hb_font_set_ptem(self->hb_font, self->scaled_point_sz);
hb_ot_font_set_funcs(self->hb_font);
hb_font_set_ptem(hb, self->scaled_point_sz);
// Setup CoreText compatible glyph lookup functions
self->hb_font = hb_font_create_sub_font(hb);
if (!self->hb_font) fatal("Failed to create sub hb_font_t");
hb_font_funcs_t *ffunctions = hb_font_funcs_create();
hb_font_set_funcs(self->hb_font, ffunctions, hb, NULL);
hb_font_funcs_set_nominal_glyph_func(ffunctions, get_nominal_glyph, NULL, NULL);
hb_font_funcs_set_variation_glyph_func(ffunctions, get_variation_glyph, NULL, NULL);
hb_font_funcs_destroy(ffunctions); // sub font retains a reference to this
hb_font_destroy(hb); // the sub font retains a reference to the parent font
}
return self->hb_font;
}