linux: hack around arabic advances in harfbuzz

Arabic vowels in some fonts (Times New Roman, at least) have
non-zero advances, when they should be zero.  Pango does a hack very
similar to this to work around the same problem.

Review URL: http://codereview.chromium.org/543067

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@36418 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 26 insertions, 1 deletions

diff --git a/third_party/harfbuzz/src/harfbuzz-arabic.c b/third_party/harfbuzz/src/harfbuzz-arabic.c
index 3837087..ce2ca6c 100644
--- a/third_party/harfbuzz/src/harfbuzz-arabic.c
+++ b/third_party/harfbuzz/src/harfbuzz-arabic.c
@@ -1107,6 +1107,7 @@ HB_Bool HB_ArabicShape(HB_ShaperItem *item)
     assert(item->item.script == HB_Script_Arabic || item->item.script == HB_Script_Syriac
            || item->item.script == HB_Script_Nko);
 
+    item->shaperFlags |= HB_ShaperFlag_ForceMarksToZeroWidth;
 #ifndef NO_OPENTYPE
 
     if (HB_SelectScript(item, item->item.script == HB_Script_Arabic ? arabic_features : syriac_features)) {
diff --git a/third_party/harfbuzz/src/harfbuzz-shaper.cpp b/third_party/harfbuzz/src/harfbuzz-shaper.cpp
index 2b0dfde..f1606e6 100644
--- a/third_party/harfbuzz/src/harfbuzz-shaper.cpp
+++ b/third_party/harfbuzz/src/harfbuzz-shaper.cpp
@@ -1189,6 +1189,24 @@ HB_Bool HB_OpenTypeShape(HB_ShaperItem *item, const hb_uint32 *properties)
     return true;
 }
 
+/* See comments near the definition of HB_ShaperFlag_ForceMarksToZeroWidth for a description
+   of why this function exists. */
+void HB_FixupZeroWidth(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;
@@ -1203,6 +1221,8 @@ HB_Bool HB_OpenTypePosition(HB_ShaperItem *item, int availableGlyphs, HB_Bool do
 
     if (!face->glyphs_substituted && !glyphs_positioned) {
         HB_GetGlyphAdvances(item);
+        if (item->face->current_flags & HB_ShaperFlag_ForceMarksToZeroWidth)
+            HB_FixupZeroWidth(item);
         return true; // nothing to do for us
     }
 
diff --git a/third_party/harfbuzz/src/harfbuzz-shaper.h b/third_party/harfbuzz/src/harfbuzz-shaper.h
index f7c7714..33fc85a 100644
--- a/third_party/harfbuzz/src/harfbuzz-shaper.h
+++ b/third_party/harfbuzz/src/harfbuzz-shaper.h
@@ -154,7 +154,11 @@ typedef enum {
 typedef enum {
     HB_ShaperFlag_Default = 0,
     HB_ShaperFlag_NoKerning = 1,
-    HB_ShaperFlag_UseDesignMetrics = 2
+    HB_ShaperFlag_UseDesignMetrics = 1 << 1,
+    /* Arabic vowels in some fonts (Times New Roman, at least) have
+       non-zero advances, when they should be zero.  Setting this shaper
+       flag causes us to zero out the advances for mark glyphs. */
+    HB_ShaperFlag_ForceMarksToZeroWidth = 1 << 2
 } HB_ShaperFlag;
 
 /*