Align drag threshold across content types.

third_party/WebKit/Source/core/input/MouseEventManager.cpp

 // Copyright 2016 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 "core/input/MouseEventManager.h"
 
 #include "core/clipboard/DataObject.h"
 #include "core/clipboard/DataTransfer.h"
 #include "core/dom/Element.h"
 #include "core/dom/ElementTraversal.h"
@@ skipping 41 matching lines @@
   String region = canvas->getIdFromControl(element);
   PlatformMouseEvent newMouseEvent = mouseEvent;
   newMouseEvent.setRegion(region);
   return newMouseEvent;
 }
 
 // The amount of time to wait before sending a fake mouse event triggered
 // during a scroll.
 const double kFakeMouseMoveInterval = 0.1;
 
+// TODO(crbug.com/653490): Read these values from the OS.
 #if OS(MACOSX)
+const int kDragThresholdX = 3;
+const int kDragThresholdY = 3;
 const double kTextDragDelay = 0.15;
 #else
+const int kDragThresholdX = 4;
+const int kDragThresholdY = 4;
 const double kTextDragDelay = 0.0;
 #endif
 
-// The link drag hysteresis is much larger than the others because there
-// needs to be enough space to cancel the link press without starting a link
-// drag, and because dragging links is rare.
-const int kLinkDragHysteresis = 40;
-const int kImageDragHysteresis = 5;
-const int kTextDragHysteresis = 3;
-const int kGeneralDragHysteresis = 3;
-
 }  // namespace
 
 enum class DragInitiator { Mouse, Touch };
 
 MouseEventManager::MouseEventManager(LocalFrame* frame,
                                      ScrollManager* scrollManager)
     : m_frame(frame),
       m_scrollManager(scrollManager),
       m_fakeMouseMoveEventTimer(
           this,
@@ skipping 689 matching lines @@
                 .mouseDownMayStartSelect() &&
            !m_mouseDownMayStartAutoscroll;
   }
 
   // We are starting a text/image/url drag, so the cursor should be an arrow
   // FIXME <rdar://7577595>: Custom cursors aren't supported during drag and
   // drop (default to pointer).
   m_frame->view()->setCursor(pointerCursor());
 
   if (initiator == DragInitiator::Mouse &&
-      !dragHysteresisExceeded(event.event().position()))
+      !dragThresholdExceeded(event.event().position()))
     return true;
 
-  // Once we're past the hysteresis point, we don't want to treat this gesture
-  // as a click
+  // Once we're past the drag threshold, we don't want to treat this gesture as
+  // a click.
   invalidateClick();
 
   if (!tryStartDrag(event)) {
     // Something failed to start the drag, clean up.
     clearDragDataTransfer();
     dragState().m_dragSrc = nullptr;
   }
 
   m_mouseDownMayStartDrag = false;
   // Whether or not the drag actually started, no more default handling (like
@@ skipping 123 matching lines @@
   // In case the drag was ended due to an escape key press we need to ensure
   // that consecutive mousemove events don't reinitiate the drag and drop.
   m_mouseDownMayStartDrag = false;
 }
 
 DragState& MouseEventManager::dragState() {
   DEFINE_STATIC_LOCAL(DragState, state, (new DragState));
   return state;
 }
 
-bool MouseEventManager::dragHysteresisExceeded(
+bool MouseEventManager::dragThresholdExceeded(
     const IntPoint& dragLocationInRootFrame) const {
   FrameView* view = m_frame->view();
   if (!view)
     return false;
   IntPoint dragLocation = view->rootFrameToContents(dragLocationInRootFrame);
   IntSize delta = dragLocation - m_mouseDownPos;
 
-  int threshold = kGeneralDragHysteresis;
-  switch (dragState().m_dragType) {
-    case DragSourceActionSelection:
-      threshold = kTextDragHysteresis;
-      break;
-    case DragSourceActionImage:
-      threshold = kImageDragHysteresis;
-      break;
-    case DragSourceActionLink:
-      threshold = kLinkDragHysteresis;
-      break;
-    case DragSourceActionDHTML:
-      break;
-    case DragSourceActionNone:
-      NOTREACHED();
-  }
+  int thresholdX = kDragThresholdX;
+  int thresholdY = kDragThresholdY;
 
-  return abs(delta.width()) >= threshold || abs(delta.height()) >= threshold;
+  // WebKit's drag thresholds depend on the type of object being dragged. If we
+  // want to revive that behavior, we can multiply the thresholds above with a
+  // constant based on dragState().m_dragType.
+
+  return abs(delta.width()) >= thresholdX || abs(delta.height()) >= thresholdY;
 }
 
 void MouseEventManager::clearDragHeuristicState() {
   // Used to prevent mouseMoveEvent from initiating a drag before
   // the mouse is pressed again.
   m_mousePressed = false;
   m_capturesDragging = false;
   m_mouseDownMayStartDrag = false;
   m_mouseDownMayStartAutoscroll = false;
 }
@@ skipping 42 matching lines @@
 
 void MouseEventManager::setClickCount(int clickCount) {
   m_clickCount = clickCount;
 }
 
 bool MouseEventManager::mouseDownMayStartDrag() {
   return m_mouseDownMayStartDrag;
 }
 
 }  // namespace blink