Ease selection dragging between large/small text lines

ui/touch_selection/touch_selection_controller_unittest.cc

 // Copyright 2014 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/touch_selection/touch_selection_controller.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/events/test/motion_event_test_utils.h"
 
 using ui::test::MockMotionEvent;
@@ skipping 712 matching lines @@
   EXPECT_FALSE(GetAndResetSelectionPointsSwapped());
   EXPECT_EQ(base_offset, GetLastSelectionStart());
   EXPECT_EQ(extent_offset + gfx::Vector2dF(0, 5), GetLastSelectionEnd());
 
   event = MockMotionEvent(MockMotionEvent::ACTION_UP, event_time, 10, 5);
   EXPECT_TRUE(controller().WillHandleTouchEvent(event));
   EXPECT_EQ(SELECTION_DRAG_STOPPED, GetLastEventType());
   EXPECT_FALSE(GetAndResetSelectionMoved());
 }
 
+TEST_F(TouchSelectionControllerTest, SelectionDragExtremeLineSize) {
+  base::TimeTicks event_time = base::TimeTicks::Now();
+  controller().OnLongPressEvent();
+
+  float small_line_height = 1.f;
+  float large_line_height = 50.f;
+  gfx::RectF small_line_rect(0, 0, 0, small_line_height);
+  gfx::RectF large_line_rect(50, 50, 0, large_line_height);
+  bool visible = true;
+  ChangeSelection(small_line_rect, visible, large_line_rect, visible);
+  EXPECT_EQ(SELECTION_SHOWN, GetLastEventType());
+  EXPECT_EQ(small_line_rect.bottom_left(), GetLastEventAnchor());
+
+  // Start dragging the handle on the small line.
+  MockMotionEvent event(MockMotionEvent::ACTION_DOWN, event_time,
+                        small_line_rect.x(), small_line_rect.y());
+  SetDraggingEnabled(true);
+  EXPECT_TRUE(controller().WillHandleTouchEvent(event));
+  EXPECT_EQ(SELECTION_DRAG_STARTED, GetLastEventType());
+  // The drag coordinate for large lines should be capped to a reasonable
+  // offset, allowing seamless transition to neighboring lines with different
+  // sizes. The drag coordinate for small lines should have an offset
+  // commensurate with the small line size.
+  EXPECT_EQ(large_line_rect.bottom_left() - gfx::Vector2dF(0, 5.f),
+            GetLastSelectionStart());
+  EXPECT_EQ(small_line_rect.CenterPoint(), GetLastSelectionEnd());
+
+  small_line_rect += gfx::Vector2dF(25.f, 0);
+  event = MockMotionEvent(MockMotionEvent::ACTION_MOVE, event_time,
+                          small_line_rect.x(), small_line_rect.y());
+  EXPECT_TRUE(controller().WillHandleTouchEvent(event));
+  EXPECT_TRUE(GetAndResetSelectionMoved());
+  EXPECT_EQ(small_line_rect.CenterPoint(), GetLastSelectionEnd());
+}
+
 TEST_F(TouchSelectionControllerTest, Animation) {
   controller().OnTapEvent();
   controller().OnSelectionEditable(true);
 
   gfx::RectF insertion_rect(5, 5, 0, 10);
 
   bool visible = true;
   ChangeInsertion(insertion_rect, visible);
   EXPECT_FALSE(GetAndResetNeedsAnimate());
 
@@ skipping 91 matching lines @@
   controller().OnSelectionEmpty(false);
   controller().HideAndDisallowShowingAutomatically();
   gfx::RectF insertion_rect(5, 5, 0, 10);
   ChangeInsertion(insertion_rect, visible);
   controller().AllowShowingFromCurrentSelection();
   EXPECT_EQ(INSERTION_SHOWN, GetLastEventType());
   EXPECT_EQ(insertion_rect.bottom_left(), GetLastEventAnchor());
 }
 
 }  // namespace ui