Improve RenderTextWin font fallback.

ui/gfx/render_text_win.cc

Index: ui/gfx/render_text_win.cc
===================================================================
--- ui/gfx/render_text_win.cc	(revision 111944)
+++ ui/gfx/render_text_win.cc	(working copy)
@@ -359,7 +359,7 @@
   return bounds;
 }
 
-bool RenderTextWin::IsCursorablePosition(size_t position) {
+bool RenderTextWin::IsCursorablePosition(size_t position, bool is_trailing) {
   if (position == 0 || position == text().length())
     return true;
 
@@ -368,6 +368,8 @@
     return false;
 
   internal::TextRun* run = runs_[run_index];
+  if (is_trailing && !run->script_analysis.fRTL)

[msw, 2011/11/29 20:42:00]

Shouldn't this be done before |GetRunContainingPosition(position);|?
What if the caret's |position| is trailing the last character of an RTL
run/string? Seems like potential out of bounds indexing...
I'm generally confused by this part of the CL; perhaps my check for cursorable
positions via comparing logical clusters is incorrect/insufficient?
At the same time, it seems odd that we were(Win)/are(Linux) checking the caret
position as cursorable without considering the LEADING/TRAILING placement.

+    position++;
   size_t start = run->range.start();
   if (position == start)
     return true;
@@ -466,6 +468,7 @@
     internal::TextRun* run = *run_iter;
     size_t run_length = run->range.length();
     const wchar_t* run_text = &(text()[run->range.start()]);
+    bool tried_fallback = false;
 
     // Select the font desired for glyph generation.
     SelectObject(hdc, run->font.GetNativeFont());
@@ -490,12 +493,15 @@
       if (hr == E_OUTOFMEMORY) {
         max_glyphs *= 2;
       } else if (hr == USP_E_SCRIPT_NOT_IN_FONT) {
-        // TODO(msw): Don't use SCRIPT_UNDEFINED. Apparently Uniscribe can crash
-        //            on certain surrogate pairs with SCRIPT_UNDEFINED.
-        //            See https://bugzilla.mozilla.org/show_bug.cgi?id=341500
-        //            And http://maxradi.us/documents/uniscribe/
-        if (run->script_analysis.eScript == SCRIPT_UNDEFINED)
-          break;
+         // Only try font fallback if it hasn't yet been attempted for this run.
+         if (tried_fallback) {
+           // TODO(msw): Don't use SCRIPT_UNDEFINED. Apparently Uniscribe can
+           //            crash on certain surrogate pairs with SCRIPT_UNDEFINED.
+           //            See https://bugzilla.mozilla.org/show_bug.cgi?id=341500
+           //            And http://maxradi.us/documents/uniscribe/
+           run->script_analysis.eScript = SCRIPT_UNDEFINED;
+           break;
+         }
 
         // The run's font doesn't contain the required glyphs, use an alternate.
         if (ChooseFallbackFont(hdc, run->font, run_text, run_length,
@@ -504,7 +510,7 @@
           SelectObject(hdc, run->font.GetNativeFont());
         }
 
-        run->script_analysis.eScript = SCRIPT_UNDEFINED;
+        tried_fallback = true;
       } else {
         break;
       }