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Follow up to variation-selector-not-found glyph

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Addresses https://github.com/harfbuzz/harfbuzz/pull/4529#discussion_r1769638033

I'm not sure if this is an improvement. By leaving the var-selector
as default-ignorable, ligatures can form around it, and the resulting
cluster won't make it clear *which* base+var-selector could not be
resolved... That doesn't quite help font fallback the way we want.
Putting up for review.
This commit is contained in:
Behdad Esfahbod 2024-09-22 08:23:34 -06:00
parent 25591a3a1d
commit b94a39d7f3
6 changed files with 36 additions and 12 deletions
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1
src/hb-buffer.hh
View file

@ -52,6 +52,7 @@ enum hb_buffer_scratch_flags_t {
HB_BUFFER_SCRATCH_FLAG_HAS_CGJ = 0x00000010u,
HB_BUFFER_SCRATCH_FLAG_HAS_GLYPH_FLAGS = 0x00000020u,
HB_BUFFER_SCRATCH_FLAG_HAS_BROKEN_SYLLABLE = 0x00000040u,
HB_BUFFER_SCRATCH_FLAG_HAS_VARIATION_SELECTOR_FALLBACK= 0x00000080u,
/* Reserved for shapers' internal use. */
HB_BUFFER_SCRATCH_FLAG_SHAPER0 = 0x01000000u,

2
src/hb-ot-layout.hh
View file

@ -173,7 +173,7 @@ _hb_next_syllable (hb_buffer_t *buffer, unsigned int start)
/* Design:
* unicode_props() is a two-byte number. The low byte includes:
* - General_Category: 5 bits.
* - Extended General_Category: 5 bits.
* - A bit each for:
* * Is it Default_Ignorable(); we have a modified Default_Ignorable().
* * Whether it's one of the four Mongolian Free Variation Selectors,

18
src/hb-ot-shape-normalize.cc
View file

@ -220,16 +220,14 @@ handle_variation_selector_cluster (const hb_ot_shape_normalize_context_t *c,
/* Just pass on the two characters separately, let GSUB do its magic. */
set_glyph (buffer->cur(), font);
(void) buffer->next_glyph ();
if (buffer->not_found_variation_selector != HB_CODEPOINT_INVALID)
{
_hb_glyph_info_clear_default_ignorable (&buffer->cur());
next_char (buffer, buffer->not_found_variation_selector);
}
else
{
set_glyph (buffer->cur(), font);
(void) buffer->next_glyph ();
}
buffer->scratch_flags |= HB_BUFFER_SCRATCH_FLAG_HAS_VARIATION_SELECTOR_FALLBACK;
_hb_glyph_info_set_general_category (&buffer->cur(),
_HB_UNICODE_GENERAL_CATEGORY_VARIATION_SELECTOR);
set_glyph (buffer->cur(), font);
(void) buffer->next_glyph ();
}
/* Skip any further variation selectors. */
while (buffer->idx < end &&

22
src/hb-ot-shape.cc
View file

@ -837,6 +837,27 @@ hb_ot_zero_width_default_ignorables (const hb_buffer_t *buffer)
pos[i].x_advance = pos[i].y_advance = pos[i].x_offset = pos[i].y_offset = 0;
}
static void
hb_ot_deal_with_variation_selectors (hb_buffer_t *buffer)
{
if (!(buffer->scratch_flags & HB_BUFFER_SCRATCH_FLAG_HAS_VARIATION_SELECTOR_FALLBACK) ||
buffer->not_found_variation_selector == HB_CODEPOINT_INVALID)
return;
unsigned int count = buffer->len;
hb_glyph_info_t *info = buffer->info;
for (unsigned int i = 0; i < count; i++)
{
if (_hb_glyph_info_get_general_category (&info[i]) ==
_HB_UNICODE_GENERAL_CATEGORY_VARIATION_SELECTOR)
{
_hb_glyph_info_clear_default_ignorable (&info[i]);
info[i].codepoint = buffer->not_found_variation_selector;
}
}
}
static void
hb_ot_hide_default_ignorables (hb_buffer_t *buffer,
hb_font_t *font)
@ -966,6 +987,7 @@ hb_ot_substitute_post (const hb_ot_shape_context_t *c)
hb_aat_layout_remove_deleted_glyphs (c->buffer);
#endif
hb_ot_deal_with_variation_selectors (c->buffer);
hb_ot_hide_default_ignorables (c->buffer, c->font);
if (c->plan->shaper->postprocess_glyphs &&

3
src/hb-unicode.hh
View file

@ -34,6 +34,9 @@
#include "hb.hh"
// Hack. See: https://github.com/harfbuzz/harfbuzz/pull/4529#discussion_r1769638033
#define _HB_UNICODE_GENERAL_CATEGORY_VARIATION_SELECTOR ((hb_unicode_general_category_t) 30)
extern HB_INTERNAL const uint8_t _hb_modified_combining_class[256];
/*

2
test/shape/data/in-house/tests/variation-selectors.tests
View file

@ -1,2 +1,2 @@
../fonts/bbc24004e776f348a0f72287d24b0124867ee750.ttf;;U+0066,U+FE00,U+0069;[gid5=0+1134|gid1=0+0]
../fonts/bbc24004e776f348a0f72287d24b0124867ee750.ttf;--not-found-variation-selector-glyph=1000000;U+0066,U+FE00,U+0069;[gid2=0+711|gid1000000=0+0|gid3=2+497]
../fonts/bbc24004e776f348a0f72287d24b0124867ee750.ttf;--not-found-variation-selector-glyph=1000000;U+0066,U+FE00,U+0069;[gid5=0+1134|gid1000000=0+0]