[GSUB] Fix mark component stuff when ligatures form ligatures!
See comments.
Fixes https://bugzilla.gnome.org/show_bug.cgi?id=437633
diff --git a/src/hb-ot-layout-gsub-table.hh b/src/hb-ot-layout-gsub-table.hh
index 2c76ae0..7c3c54c 100644
--- a/src/hb-ot-layout-gsub-table.hh
+++ b/src/hb-ot-layout-gsub-table.hh
@@ -485,8 +485,45 @@
hb_apply_context_t::mark_skipping_forward_iterator_t skippy_iter (c, c->buffer->idx, count - 1);
if (skippy_iter.has_no_chance ()) return TRACE_RETURN (false);
- bool first_was_mark = (c->property & HB_OT_LAYOUT_GLYPH_CLASS_MARK);
- bool found_non_mark = false;
+ /*
+ * This is perhaps the trickiest part of GSUB... Remarks:
+ *
+ * - If all components of the ligature were marks, we call this a mark ligature.
+ *
+ * - If there is no GDEF, and the ligature is NOT a mark ligature, we categorize
+ * it as a ligature glyph. Though, really, this will not really be used...
+ *
+ * - If it *is* a mark ligature, we don't allocate a new ligature id, and leave
+ * the ligature to keep its old ligature id. This will allow it to attach to
+ * a base ligature in GPOS. Eg. if the sequence is: LAM,LAM,SHADDA,FATHA,HEH,
+ * and LAM,LAM,HEH for a ligature, they will leave SHADDA and FATHA wit a
+ * ligature id and component value of 2. Then if SHADDA,FATHA form a ligature
+ * later, we don't want them to lose their ligature id/component, otherwise
+ * GPOS will fail to correctly position the mark ligature on top of the
+ * LAM,LAM,HEH ligature. See:
+ * https://bugzilla.gnome.org/show_bug.cgi?id=676343
+ *
+ * - If a ligature is formed of components that some of which are also ligatures
+ * themselves, and those ligature components had marks attached to *their*
+ * components, we have to attach the marks to the new ligature component
+ * positions! Now *that*'s tricky! And these marks may be following the
+ * last component of the whole sequence, so we should loop forward looking
+ * for them and update them.
+ *
+ * Eg. the sequence is LAM,LAM,SHADDA,FATHA,HEH, and the font first forms a
+ * 'clig' ligature of LAM,HEH, leaving the SHADDA and FATHA with a ligature
+ * id and component == 1. Now, during 'liga', the LAM and the LAM-HEH ligature
+ * form a LAM-LAM-HEH ligature. We need to reassign the SHADDA and FATHA to
+ * the new ligature with a component value of 2.
+ *
+ * This in fact happened to a font... See:
+ * https://bugzilla.gnome.org/show_bug.cgi?id=437633
+ */
+
+ bool is_mark_ligature = !!(c->property & HB_OT_LAYOUT_GLYPH_CLASS_MARK);
+
+ unsigned int total_component_count = 0;
+ total_component_count += get_lig_num_comps (c->buffer->cur());
for (unsigned int i = 1; i < count; i++)
{
@@ -494,54 +531,54 @@
if (!skippy_iter.next (&property)) return TRACE_RETURN (false);
- found_non_mark |= !(property & HB_OT_LAYOUT_GLYPH_CLASS_MARK);
-
if (likely (c->buffer->info[skippy_iter.idx].codepoint != component[i])) return TRACE_RETURN (false);
+
+ is_mark_ligature = is_mark_ligature && (property & HB_OT_LAYOUT_GLYPH_CLASS_MARK);
+ total_component_count += get_lig_num_comps (c->buffer->info[skippy_iter.idx]);
}
- bool is_a_mark_ligature = first_was_mark && !found_non_mark;
+ /* Deal, we are forming the ligature. */
+ c->buffer->merge_clusters (c->buffer->idx, skippy_iter.idx + 1);
- unsigned int klass = is_a_mark_ligature ? 0 : HB_OT_LAYOUT_GLYPH_CLASS_LIGATURE;
+ unsigned int klass = is_mark_ligature ? 0 : HB_OT_LAYOUT_GLYPH_CLASS_LIGATURE;
+ unsigned int lig_id = is_mark_ligature ? 0 : allocate_lig_id (c->buffer);
+ unsigned int last_lig_id = get_lig_id (c->buffer->cur());
+ unsigned int last_num_components = get_lig_num_comps (c->buffer->cur());
+ unsigned int components_so_far = last_num_components;
- /* If it's a mark ligature, we should leave the lig_id / lig_comp alone such that
- * the resulting mark ligature has the opportunity to attach to ligature components
- * of it's base later on. See for example:
- * https://bugzilla.gnome.org/show_bug.cgi?id=676343
- */
+ if (!is_mark_ligature)
+ set_lig_props_for_ligature (c->buffer->cur(), lig_id, total_component_count);
+ c->replace_glyph (ligGlyph, klass);
- /* Allocate new ligature id */
- unsigned int lig_id = is_a_mark_ligature ? 0 : allocate_lig_id (c->buffer);
- if (!is_a_mark_ligature)
- set_lig_props_for_ligature (c->buffer->cur(), lig_id, count);
-
- if (skippy_iter.idx < c->buffer->idx + count) /* No input glyphs skipped */
+ for (unsigned int i = 1; i < count; i++)
{
- hb_codepoint_t lig_glyph = ligGlyph;
- c->replace_glyphs (count, 1, &lig_glyph, klass);
- }
- else
- {
- c->buffer->merge_clusters (c->buffer->idx, skippy_iter.idx + 1);
- c->replace_glyph (ligGlyph);
-
- /* Now we must do a second loop to copy the skipped glyphs to
- `out' and assign component values to it. We start with the
- glyph after the first component. Glyphs between component
- i and i+1 belong to component i. Together with the lig_id
- value it is later possible to check whether a specific
- component value really belongs to a given ligature. */
-
- for (unsigned int i = 1; i < count; i++)
+ while (c->should_mark_skip_current_glyph ())
{
- while (c->should_mark_skip_current_glyph ())
- {
- if (!is_a_mark_ligature)
- set_lig_props_for_mark (c->buffer->cur(), lig_id, i);
- c->buffer->next_glyph ();
+ if (!is_mark_ligature) {
+ unsigned int new_lig_comp = components_so_far - last_num_components +
+ MIN (MAX (get_lig_comp (c->buffer->cur()), 1), last_num_components);
+ set_lig_props_for_mark (c->buffer->cur(), lig_id, new_lig_comp);
}
+ c->buffer->next_glyph ();
+ }
- /* Skip the base glyph */
- c->buffer->idx++;
+ last_lig_id = get_lig_id (c->buffer->cur());
+ last_num_components = get_lig_num_comps (c->buffer->cur());
+ components_so_far += last_num_components;
+
+ /* Skip the base glyph */
+ c->buffer->idx++;
+ }
+
+ if (!is_mark_ligature && last_lig_id) {
+ /* Re-adjust components for any marks following. */
+ for (unsigned int i = c->buffer->idx; i < c->buffer->len; i++) {
+ if (last_lig_id == get_lig_id (c->buffer->info[i])) {
+ unsigned int new_lig_comp = components_so_far - last_num_components +
+ MIN (MAX (get_lig_comp (c->buffer->info[i]), 1), last_num_components);
+ set_lig_props_for_mark (c->buffer->info[i], lig_id, new_lig_comp);
+ } else
+ break;
}
}
