Make PointerEvent coordinates fractional for touch

third_party/WebKit/Source/core/events/MouseRelatedEvent.h

 /*
  * Copyright (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2001 Tobias Anton (anton@stud.fbi.fh-darmstadt.de)
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 25 matching lines @@
  public:
   enum class PositionType {
     Position,
     // Positionless mouse events are used, for example, for 'click' events from
     // keyboard input.  It's kind of surprising for a mouse event not to have a
     // position.
     Positionless
   };
   // Note that these values are adjusted to counter the effects of zoom, so that
   // values exposed via DOM APIs are invariant under zooming.
-  int screenX() const { return m_screenLocation.x(); }
-  int screenY() const { return m_screenLocation.y(); }
-  const IntPoint& screenLocation() const { return m_screenLocation; }
-  int clientX() const { return m_clientLocation.x().toInt(); }
-  int clientY() const { return m_clientLocation.y().toInt(); }
+  double screenX() const {
+    return isPointerEvent() ? m_screenLocation.x().toDouble()

[Rick Byers, 2016/10/12 14:09:54]

It seems odd that this pattern of conditional return values is necessary.  Can't
you just initialize the event in the first place to truncate to integers for
mouse events but not for pointer events?

[mustaq, 2016/10/12 16:00:01]

The problem here is that the initialization is done at MouseRelatedEvent
constructors where the vtable for the actual subclass being constructed (e.g.
MouseEvent or PointerEvent) is not "ready". As a result, all isXyzEvent()
functions return false.

+                            : m_screenLocation.x().toInt();
+  }
+  double screenY() const {
+    return isPointerEvent() ? m_screenLocation.y().toDouble()
+                            : m_screenLocation.y().toInt();
+  }
+  double clientX() const {
+    return isPointerEvent() ? m_clientLocation.x().toDouble()
+                            : m_clientLocation.x().toInt();
+  }
+  double clientY() const {
+    return isPointerEvent() ? m_clientLocation.y().toDouble()
+                            : m_clientLocation.y().toInt();
+  }
   int movementX() const { return m_movementDelta.x().toInt(); }
   int movementY() const { return m_movementDelta.y().toInt(); }
-  const LayoutPoint& clientLocation() const { return m_clientLocation; }
   int layerX();
   int layerY();
   int offsetX();
   int offsetY();
   int pageX() const;
   int pageY() const;
   int x() const;
   int y() const;
   bool hasPosition() const { return m_positionType == PositionType::Position; }
 
@@ skipping 19 matching lines @@
                     const IntPoint& rootFrameLocation,
                     const IntPoint& movementDelta,
                     PlatformEvent::Modifiers,
                     double platformTimeStamp,
                     PositionType,
                     InputDeviceCapabilities* sourceCapabilities = nullptr);
 
   MouseRelatedEvent(const AtomicString& type,
                     const MouseEventInit& initializer);
 
-  void initCoordinates(const LayoutPoint& clientLocation);
+  void initCoordinates(const double clientX, const double clientY);
   void receivedTarget() final;
 
   void computePageLocation();
   void computeRelativePosition();
 
   // Expose these so MouseEvent::initMouseEvent can set them.
-  IntPoint m_screenLocation;
+  LayoutPoint m_screenLocation;
   LayoutPoint m_clientLocation;
   LayoutPoint m_movementDelta;
 
  private:
   LayoutPoint m_pageLocation;
   LayoutPoint m_layerLocation;
   LayoutPoint m_offsetLocation;
   LayoutPoint m_absoluteLocation;
   PositionType m_positionType;
   bool m_hasCachedRelativePosition;
 };
 
 }  // namespace blink
 
 #endif  // MouseRelatedEvent_h