Don't paint text outside display area

ui/gfx/render_text_pango.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/render_text_pango.h"
 
 #include <pango/pangocairo.h>
 #include <algorithm>
 #include <string>
 #include <vector>
@@ skipping 392 matching lines @@
   ApplyTextShadows(&renderer);
   renderer.SetFontRenderParams(
       font_list().GetPrimaryFont().GetFontRenderParams(),
       background_is_transparent());
 
   // Temporarily apply composition underlines and selection colors.
   ApplyCompositionAndSelectionStyles();
 
   internal::StyleIterator style(colors(), styles());
   for (GSList* it = current_line_->runs; it; it = it->next) {
+    // Skip painting runs outside the display area.
+    if (SkScalarTruncToInt(x) >= display_rect().right())
+      break;
+
     PangoLayoutRun* run = reinterpret_cast<PangoLayoutRun*>(it->data);
     int glyph_count = run->glyphs->num_glyphs;
-    // TODO(msw): Skip painting runs outside the display rect area, like Win.
     if (glyph_count == 0)
       continue;
 
     ScopedPangoFontDescription desc(
         pango_font_describe(run->item->analysis.font));
     const std::string family_name =
         pango_font_description_get_family(desc.get());
     renderer.SetTextSize(GetPangoFontSizeInPixels(desc.get()));
 
     glyphs.resize(glyph_count);
@@ skipping 13 matching lines @@
     do {
       const PangoGlyphInfo& glyph = run->glyphs->glyphs[glyph_index];
       glyphs[glyph_index] = static_cast<uint16>(glyph.glyph);
       // Use pango_units_to_double() rather than PANGO_PIXELS() here, so units
       // are not rounded to the pixel grid if subpixel positioning is enabled.
       pos[glyph_index].set(x + pango_units_to_double(glyph.geometry.x_offset),
                            y + pango_units_to_double(glyph.geometry.y_offset));
       x += pango_units_to_double(glyph.geometry.width);
 
       ++glyph_index;
+      // If this is the last glyph of the range or the last glyph inside the
+      // display area (which would cause early termination of the loop), paint
+      // the range.
       const size_t glyph_text_index = (glyph_index == glyph_count) ?
           style_range.end() : GetGlyphTextIndex(run, glyph_index);
-      if (!IndexInRange(style_range, glyph_text_index)) {
+      if (!IndexInRange(style_range, glyph_text_index) ||
+          SkScalarTruncToInt(x) >= display_rect().right()) {
         // TODO(asvitkine): For cases like "fi", where "fi" is a single glyph
         //                  but can span multiple styles, Pango splits the
         //                  styles evenly over the glyph. We can do this too by
         //                  clipping and drawing the glyph several times.
         renderer.SetForegroundColor(style.color());
         const int font_style = (style.style(BOLD) ? Font::BOLD : 0) |
                                (style.style(ITALIC) ? Font::ITALIC : 0);
         renderer.SetFontFamilyWithStyle(family_name, font_style);
         renderer.DrawPosText(&pos[style_start_glyph_index],
                              &glyphs[style_start_glyph_index],
                              glyph_index - style_start_glyph_index);
         if (style.style(UNDERLINE))
           SetPangoUnderlineMetrics(desc.get(), &renderer);
         renderer.DrawDecorations(style_start_x, y, x - style_start_x,
                                  style.style(UNDERLINE), style.style(STRIKE),
                                  style.style(DIAGONAL_STRIKE));
         style.UpdatePosition(glyph_text_index);
         style_range = style.GetRange();
         style_start_glyph_index = glyph_index;
         style_start_x = x;
       }
-    } while (glyph_index < glyph_count);
+      // Terminates loop when the end of the range has been reached or the next
+      // glyph falls outside the display area.
+    } while (glyph_index < glyph_count &&
+             SkScalarTruncToInt(x) < display_rect().right());
   }
 
   renderer.EndDiagonalStrike();
 
   // Undo the temporarily applied composition underlines and selection colors.
   UndoCompositionAndSelectionStyles();
 }
 
 GSList* RenderTextPango::GetRunContainingCaret(
     const SelectionModel& caret) const {
@@ skipping 28 matching lines @@
                                           int glyph_index) const {
   return LayoutIndexToTextIndex(run->item->offset +
                                 run->glyphs->log_clusters[glyph_index]);
 }
 
 RenderText* RenderText::CreateNativeInstance() {
   return new RenderTextPango;
 }
 
 }  // namespace gfx