Clamp RunInfo::num_characters when shaping ranges with context

third_party/WebKit/Source/platform/fonts/shaping/HarfBuzzShaper.cpp

 /*
  * Copyright (c) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 BlackBerry Limited. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 209 matching lines @@
 
     // Compute the range indices of consecutive shaped or .notdef glyphs.
     // Cluster information for RTL runs becomes reversed, e.g. character 0
     // has cluster index 5 in a run of 6 characters.
     unsigned num_characters = 0;
     unsigned num_glyphs_to_insert = 0;
     unsigned start_index = 0;
     if (HB_DIRECTION_IS_FORWARD(hb_buffer_get_direction(range_data->buffer))) {
       start_index = glyph_info[last_change_position].cluster;
       if (glyph_index == num_glyphs) {
-        num_characters = current_queue_item.start_index_ +
-                         current_queue_item.num_characters_ -
-                         glyph_info[last_change_position].cluster;
+        // Clamp the end offsets of the queue item to the offsets representing
+        // the shaping window.
+        unsigned shape_end =
+            std::min(range_data->end, current_queue_item.start_index_ +
+                                          current_queue_item.num_characters_);
+        num_characters = shape_end - glyph_info[last_change_position].cluster;
         num_glyphs_to_insert = num_glyphs - last_change_position;
       } else {
         num_characters = glyph_info[glyph_index].cluster -
                          glyph_info[last_change_position].cluster;
         num_glyphs_to_insert = glyph_index - last_change_position;
       }
     } else {
       // Direction Backwards
       start_index = glyph_info[glyph_index - 1].cluster;
       if (last_change_position == 0) {
-        num_characters = current_queue_item.start_index_ +
-                         current_queue_item.num_characters_ -
-                         glyph_info[glyph_index - 1].cluster;
+        // Clamp the end offsets of the queue item to the offsets representing
+        // the shaping window.
+        unsigned shape_end =
+            std::min(range_data->end, current_queue_item.start_index_ +
+                                          current_queue_item.num_characters_);
+        num_characters = shape_end - glyph_info[glyph_index - 1].cluster;
       } else {
         num_characters = glyph_info[last_change_position - 1].cluster -
                          glyph_info[glyph_index - 1].cluster;
       }
       num_glyphs_to_insert = glyph_index - last_change_position;
     }
 
     if (current_cluster_result == kShaped && !is_last_resort) {
       // Now it's clear that we need to continue processing.
       if (!font_cycle_queued) {
@@ skipping 457 matching lines @@
   }
   return result.Release();
 }
 
 PassRefPtr<ShapeResult> HarfBuzzShaper::Shape(const Font* font,
                                               TextDirection direction) const {
   return Shape(font, direction, 0, text_length_);
 }
 
 }  // namespace blink