RenderText: Allow setting display offset explicitly

ui/gfx/render_text.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.h"
 
 #include <algorithm>
 #include <climits>
 
 #include "base/command_line.h"
@@ skipping 854 matching lines @@
 }
 
 SelectionModel RenderText::GetSelectionModelForSelectionStart() {
   const Range& sel = selection();
   if (sel.is_empty())
     return selection_model_;
   return SelectionModel(sel.start(),
                         sel.is_reversed() ? CURSOR_BACKWARD : CURSOR_FORWARD);
 }
 
+const Vector2d& RenderText::GetUpdatedDisplayOffset() {
+  UpdateCachedBoundsAndOffset();
+  return display_offset_;
+}
+
+void RenderText::SetDisplayOffset(const Vector2d& offset) {

[msw, 2014/07/08 17:38:23]

nit: perhaps this should only take a horizontal offset value for now?
(that'll avoid the need to pass in GetUpdatedDisplayOffset().y())

[mohsen, 2014/07/08 18:36:16]

Done.

+  int display_width = display_rect_.width();
+  int content_width = GetContentWidth();
+  int negate_rtl = horizontal_alignment_ == ALIGN_RIGHT ? -1 : 1;
+
+  Vector2d final_offset = offset;
+  if (content_width <= display_width)
+    final_offset.set_x(0);
+  else if (negate_rtl * final_offset.x() > 0)
+    final_offset.set_x(0);

[msw, 2014/07/08 17:38:23]

q: does this prevent scrolling before the start of the text?

[mohsen, 2014/07/08 18:36:16]

Yes.

+  else if (negate_rtl * final_offset.x() < display_width - content_width)
+    final_offset.set_x(negate_rtl * (display_width - content_width));
+  cached_bounds_and_offset_valid_ = true;
+  display_offset_ = final_offset;
+  cursor_bounds_ = GetCursorBounds(selection_model_, insert_mode_);
+}
+
 RenderText::RenderText()
     : horizontal_alignment_(base::i18n::IsRTL() ? ALIGN_RIGHT : ALIGN_LEFT),
       directionality_mode_(DIRECTIONALITY_FROM_TEXT),
       text_direction_(base::i18n::UNKNOWN_DIRECTION),
       cursor_enabled_(true),
       cursor_visible_(false),
       insert_mode_(true),
       cursor_color_(kDefaultColor),
       selection_color_(kDefaultColor),
       selection_background_focused_color_(kDefaultSelectionBackgroundColor),
       focused_(false),
       composition_range_(Range::InvalidRange()),
       colors_(kDefaultColor),
       styles_(NUM_TEXT_STYLES),
       composition_and_selection_styles_applied_(false),
       obscured_(false),
       obscured_reveal_index_(-1),
       truncate_length_(0),
       elide_behavior_(TRUNCATE),
       multiline_(false),
       background_is_transparent_(false),
       clip_to_display_rect_(true),
       baseline_(kInvalidBaseline),
       cached_bounds_and_offset_valid_(false) {
 }
 
-const Vector2d& RenderText::GetUpdatedDisplayOffset() {
-  UpdateCachedBoundsAndOffset();
-  return display_offset_;
-}
-
 SelectionModel RenderText::GetAdjacentSelectionModel(
     const SelectionModel& current,
     BreakType break_type,
     VisualCursorDirection direction) {
   EnsureLayout();
 
   if (break_type == LINE_BREAK || text().empty())
     return EdgeSelectionModel(direction);
   if (break_type == CHARACTER_BREAK)
     return AdjacentCharSelectionModel(current, direction);
@@ skipping 399 matching lines @@
   cursor_bounds_ += delta_offset;
 }
 
 void RenderText::DrawSelection(Canvas* canvas) {
   const std::vector<Rect> sel = GetSubstringBounds(selection());
   for (std::vector<Rect>::const_iterator i = sel.begin(); i < sel.end(); ++i)
     canvas->FillRect(*i, selection_background_focused_color_);
 }
 
 }  // namespace gfx