linux: hack around arabic advances in harfbuzz

third_party/harfbuzz/src/harfbuzz-shaper.cpp

 /*
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  * This is part of HarfBuzz, an OpenType Layout engine library.
  *
  * Permission is hereby granted, without written agreement and without
  * license or royalty fees, to use, copy, modify, and distribute this
  * software and its documentation for any purpose, provided that the
  * above copyright notice and the following two paragraphs appear in
  * all copies of this software.
@@ skipping 1171 matching lines @@
     DEBUG("shaped glyphs:");
     for (int i = 0; i < length; ++i)
         DEBUG("   glyph=%4x", hb_buffer->in_string[i].gindex);
     DEBUG("-----------------------------------------");
 //     dump_string(hb_buffer);
 #endif
 
     return true;
 }
 
+/* See comments near the definition of HB_ShaperFlag_ArabicHack for a description
+   of why this function exists. */
+void HB_FixupArabicZeroWidth(HB_ShaperItem *item)
+{
+    HB_UShort property;
+
+    if (!item->face->gdef)
+        return;
+
+    for (unsigned int i = 0; i < item->num_glyphs; ++i) {
+        /* If the glyph is a mark, force its advance to zero. */
+        if (HB_GDEF_Get_Glyph_Property (item->face->gdef, item->glyphs[i], &property) == HB_Err_Ok &&
+            property == HB_GDEF_MARK) {
+            item->advances[i] = 0;
+        }
+    }
+}
+
 HB_Bool HB_OpenTypePosition(HB_ShaperItem *item, int availableGlyphs, HB_Bool doLogClusters)
 {
     HB_Face face = item->face;
 
     bool glyphs_positioned = false;
     if (face->gpos) {
         if (face->buffer->positions)
             memset(face->buffer->positions, 0, face->buffer->in_length*sizeof(HB_PositionRec));
         // #### check that passing "false,false" is correct
         glyphs_positioned = HB_GPOS_Apply_String(item->font, face->gpos, face->current_flags, face->buffer, false, false) != HB_Err_Not_Covered;
     }
 
     if (!face->glyphs_substituted && !glyphs_positioned) {
         HB_GetGlyphAdvances(item);
+        if (item->face->current_flags & HB_ShaperFlag_ArabicHack)
+            HB_FixupArabicZeroWidth(item);
         return true; // nothing to do for us
     }
 
     // make sure we have enough space to write everything back
     if (availableGlyphs < (int)face->buffer->in_length) {
         item->num_glyphs = face->buffer->in_length;
         return false;
     }
 
     HB_Glyph *glyphs = item->glyphs;
@@ skipping 112 matching lines @@
     if (shaper_item->num_glyphs < shaper_item->item.length) {
         shaper_item->num_glyphs = shaper_item->item.length;
         return false;
     }
     assert(shaper_item->item.script < HB_ScriptCount);
     result = HB_ScriptEngines[shaper_item->item.script].shape(shaper_item);
     shaper_item->glyphIndicesPresent = false;
     return result;
 }