RenderText: Allow setting display offset explicitly

ui/gfx/render_text.cc

Index: ui/gfx/render_text.cc
diff --git a/ui/gfx/render_text.cc b/ui/gfx/render_text.cc
index 4e7281c11695d4b7b70beb85b36e04227f425936..0d4a67a75cf5785824f10d8118a6f57b93e161d2 100644
--- a/ui/gfx/render_text.cc
+++ b/ui/gfx/render_text.cc
@@ -872,6 +872,28 @@ SelectionModel RenderText::GetSelectionModelForSelectionStart() {
                         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),
@@ -898,11 +920,6 @@ RenderText::RenderText()
       cached_bounds_and_offset_valid_(false) {
 }
 
-const Vector2d& RenderText::GetUpdatedDisplayOffset() {
-  UpdateCachedBoundsAndOffset();
-  return display_offset_;
-}
-
 SelectionModel RenderText::GetAdjacentSelectionModel(
     const SelectionModel& current,
     BreakType break_type,