bug 727736 - [harfbuzz] force glyphs for zero-width diacritics to actually have zero width, to work around bad fonts. r=behdad

gfx/harfbuzz/src/hb-ot-layout.cc

@@ -32,6 +32,7 @@
 #include "hb-ot-layout-gsub-table.hh"
 #include "hb-ot-layout-gpos-table.hh"
 #include "hb-ot-maxp-table.hh"
+#include "hb-ot-shape-private.hh"
 
 
 #include <stdlib.h>
@@ -496,8 +497,46 @@ hb_ot_layout_position_lookup   (hb_font_t    *font,
 }
 
 void
-hb_ot_layout_position_finish (hb_buffer_t  *buffer)
+hb_ot_layout_position_finish (hb_face_t *face, hb_buffer_t *buffer)
 {
+  /* force diacritics to have zero width */
+  unsigned int count = buffer->len;
+  if (hb_ot_layout_has_glyph_classes (face)) {
+    const GDEF& gdef = _get_gdef (face);
+    if (buffer->props.direction == HB_DIRECTION_RTL) {
+      for (unsigned int i = 1; i < count; i++) {
+        if (gdef.get_glyph_class (buffer->info[i].codepoint) == GDEF::MarkGlyph) {
+          buffer->pos[i].x_advance = 0;
+        }
+      }
+    } else {
+      for (unsigned int i = 1; i < count; i++) {
+        if (gdef.get_glyph_class (buffer->info[i].codepoint) == GDEF::MarkGlyph) {
+          hb_glyph_position_t& pos = buffer->pos[i];
+          pos.x_offset -= pos.x_advance;
+          pos.x_advance = 0;
+        }
+      }
+    }
+  } else {
+    /* no GDEF classes available, so use General Category as a fallback */
+    if (buffer->props.direction == HB_DIRECTION_RTL) {
+      for (unsigned int i = 1; i < count; i++) {
+        if (buffer->info[i].general_category() == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) {
+          buffer->pos[i].x_advance = 0;
+        }
+      }
+    } else {
+      for (unsigned int i = 1; i < count; i++) {
+        if (buffer->info[i].general_category() == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK) {
+          hb_glyph_position_t& pos = buffer->pos[i];
+          pos.x_offset -= pos.x_advance;
+          pos.x_advance = 0;
+        }
+      }
+    }
+  }
+
   GPOS::position_finish (buffer);
 }
 

gfx/harfbuzz/src/hb-ot-layout.h

@@ -199,7 +199,7 @@ hb_ot_layout_position_lookup (hb_font_t    *font,
 
 /* Should be called after all the position_lookup's are done */
 void
-hb_ot_layout_position_finish (hb_buffer_t  *buffer);
+hb_ot_layout_position_finish (hb_face_t *face, hb_buffer_t *buffer);
 
 
 HB_END_DECLS

gfx/harfbuzz/src/hb-ot-shape.cc

@@ -299,15 +299,36 @@ hb_ot_position_complex (hb_ot_shape_context_t *c)
     c->applied_position_complex = TRUE;
   }
 
-  hb_ot_layout_position_finish (c->buffer);
+  hb_ot_layout_position_finish (c->face, c->buffer);
 
   return;
 }
 
 static void
-hb_position_complex_fallback (hb_ot_shape_context_t *c HB_UNUSED)
+hb_position_complex_fallback (hb_ot_shape_context_t *c)
 {
-  /* TODO Mark pos */
+  unsigned int count = c->buffer->len;
+  if (c->buffer->props.direction == HB_DIRECTION_RTL) {
+    for (unsigned int i = 1; i < count; i++) {
+      unsigned int gen_cat = c->buffer->info[i].general_category();
+      if ((1<<gen_cat) & ((1<<HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)|
+                          (1<<HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK)|
+                          (1<<HB_UNICODE_GENERAL_CATEGORY_FORMAT))) {
+        c->buffer->pos[i].x_advance = 0;
+      }
+    }
+  } else {
+    for (unsigned int i = 1; i < count; i++) {
+      unsigned int gen_cat = c->buffer->info[i].general_category();
+      if ((1<<gen_cat) & ((1<<HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)|
+                          (1<<HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK)|
+                          (1<<HB_UNICODE_GENERAL_CATEGORY_FORMAT))) {
+        hb_glyph_position_t& pos = c->buffer->pos[i];
+        pos.x_offset = -pos.x_advance;
+        pos.x_advance = 0;
+      }
+    }
+  }
 }
 
 static void