Detect missing glyphs as returned by Vista in RenderTextWin.

ui/gfx/render_text_win.cc

Index: ui/gfx/render_text_win.cc
===================================================================
--- ui/gfx/render_text_win.cc	(revision 134923)
+++ ui/gfx/render_text_win.cc	(working copy)
@@ -653,6 +653,23 @@
             glyphs_missing = true;
             break;
           }
+
+          // On Vista, when trying to draw Simplified Chinese via font linking,

[msw, 2012/05/02 22:19:09]

Perhaps generalize this comment if there may be other plaform/font triggers.
Consider mentioning the bug.

[Alexei Svitkine (slow), 2012/05/03 14:37:20]

Done.

+          // missing glyphs in the Meiryo font are returned as wgBlank instead
+          // of wgDefault, with fZeroWidth set.
+          if (run->glyphs[i] == properties.wgBlank &&
+              run->visible_attributes[i].fZeroWidth) {
+            // Check whether this glyph corresponds entirely to whitespace. If
+            // it doesn't, assume there are missing glyphs.
+            const ui::Range range = GetTextRangeForRunGlyph(run, i);
+            DCHECK_NE(0U, range.length());

[msw, 2012/05/02 22:19:09]

Use DCHECK_GT? Also DCHECK_LT/LE(range.end(), run->range.end()))?

+
+            const string16 glyph_text(&run_text[range.start()], range.length());
+            if (!ContainsOnlyWhitespace(glyph_text)) {
+               glyphs_missing = true;
+               break;
+            }
+          }
         }
       }
 
@@ -804,17 +821,32 @@
 }
 
 SelectionModel RenderTextWin::FirstSelectionModelInsideRun(
-    internal::TextRun* run) {
+    const internal::TextRun* run) {
   size_t cursor = IndexOfAdjacentGrapheme(run->range.start(), CURSOR_FORWARD);
   return SelectionModel(cursor, CURSOR_BACKWARD);
 }
 
 SelectionModel RenderTextWin::LastSelectionModelInsideRun(
-    internal::TextRun* run) {
+    const internal::TextRun* run) {
   size_t caret = IndexOfAdjacentGrapheme(run->range.end(), CURSOR_BACKWARD);
   return SelectionModel(caret, CURSOR_FORWARD);
 }
 
+ui::Range RenderTextWin::GetTextRangeForRunGlyph(const internal::TextRun* run,
+                                                 size_t glyph_index) const {
+  int first_seen = -1;
+  int last_seen = -1;
+  for (size_t char_index = 0; char_index < run->range.length(); ++char_index) {
+    if (run->logical_clusters[char_index] == glyph_index) {
+      last_seen = char_index;
+      if (first_seen == -1)
+        first_seen = char_index;
+    }
+  }
+  DCHECK_NE(first_seen, -1);
+  return ui::Range(first_seen, last_seen + 1);
+}
+
 RenderText* RenderText::CreateRenderText() {
   return new RenderTextWin;
 }