[use] Copy Sinhala decompositions from Indic shaper
diff --git a/src/hb-ot-shape-complex-use.cc b/src/hb-ot-shape-complex-use.cc
index 0ca088b..75aabc8 100644
--- a/src/hb-ot-shape-complex-use.cc
+++ b/src/hb-ot-shape-complex-use.cc
@@ -162,11 +162,38 @@
map->enable_feature (positioning_features[i]);
}
+struct would_substitute_feature_t
+{
+ inline void init (const hb_ot_map_t *map, hb_tag_t feature_tag, bool zero_context_)
+ {
+ zero_context = zero_context_;
+ map->get_stage_lookups (0/*GSUB*/,
+ map->get_feature_stage (0/*GSUB*/, feature_tag),
+ &lookups, &count);
+ }
+
+ inline bool would_substitute (const hb_codepoint_t *glyphs,
+ unsigned int glyphs_count,
+ hb_face_t *face) const
+ {
+ for (unsigned int i = 0; i < count; i++)
+ if (hb_ot_layout_lookup_would_substitute_fast (face, lookups[i].index, glyphs, glyphs_count, zero_context))
+ return true;
+ return false;
+ }
+
+ private:
+ const hb_ot_map_t::lookup_map_t *lookups;
+ unsigned int count;
+ bool zero_context;
+};
+
struct use_shape_plan_t
{
ASSERT_POD ();
hb_mask_t rphf_mask;
+ would_substitute_feature_t pstf; /* Needed for Sinhala decompositions. Meh. */
arabic_shape_plan_t *arabic_plan;
};
@@ -214,6 +241,8 @@
use_plan->rphf_mask = plan->map.get_1_mask (HB_TAG('r','p','h','f'));
+ use_plan->pstf.init (&plan->map, HB_TAG('p','s','t','f'), true);
+
if (has_arabic_joining (plan->props.script))
{
use_plan->arabic_plan = (arabic_shape_plan_t *) data_create_arabic (plan);
@@ -572,6 +601,58 @@
}
static bool
+decompose_use (const hb_ot_shape_normalize_context_t *c,
+ hb_codepoint_t ab,
+ hb_codepoint_t *a,
+ hb_codepoint_t *b)
+{
+ if ((ab == 0x0DDAu || hb_in_range<hb_codepoint_t> (ab, 0x0DDCu, 0x0DDEu)))
+ {
+ /*
+ * Sinhala split matras... Let the fun begin.
+ *
+ * These four characters have Unicode decompositions. However, Uniscribe
+ * decomposes them "Khmer-style", that is, it uses the character itself to
+ * get the second half. The first half of all four decompositions is always
+ * U+0DD9.
+ *
+ * Now, there are buggy fonts, namely, the widely used lklug.ttf, that are
+ * broken with Uniscribe. But we need to support them. As such, we only
+ * do the Uniscribe-style decomposition if the character is transformed into
+ * its "sec.half" form by the 'pstf' feature. Otherwise, we fall back to
+ * Unicode decomposition.
+ *
+ * Note that we can't unconditionally use Unicode decomposition. That would
+ * break some other fonts, that are designed to work with Uniscribe, and
+ * don't have positioning features for the Unicode-style decomposition.
+ *
+ * Argh...
+ *
+ * The Uniscribe behavior is now documented in the newly published Sinhala
+ * spec in 2012:
+ *
+ * https://docs.microsoft.com/en-us/typography/script-development/sinhala#shaping
+ */
+
+ const use_shape_plan_t *use_plan = (const use_shape_plan_t *) c->plan->data;
+
+ hb_codepoint_t glyph;
+
+ if (hb_options ().uniscribe_bug_compatible ||
+ (c->font->get_nominal_glyph (ab, &glyph) &&
+ use_plan->pstf.would_substitute (&glyph, 1, c->font->face)))
+ {
+ /* Ok, safe to use Uniscribe-style decomposition. */
+ *a = 0x0DD9u;
+ *b = ab;
+ return true;
+ }
+ }
+
+ return (bool) c->unicode->decompose (ab, a, b);
+}
+
+static bool
compose_use (const hb_ot_shape_normalize_context_t *c,
hb_codepoint_t a,
hb_codepoint_t b,
@@ -594,7 +675,7 @@
nullptr, /* preprocess_text */
nullptr, /* postprocess_glyphs */
HB_OT_SHAPE_NORMALIZATION_MODE_COMPOSED_DIACRITICS_NO_SHORT_CIRCUIT,
- nullptr, /* decompose */
+ decompose_use,
compose_use,
setup_masks_use,
nullptr, /* disable_otl */
