Added experimental Touch.tilt, Touch.tiltDirection support for Android

ui/events/gesture_detection/motion_event.h

 // 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.
 
 #ifndef UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_H_
 #define UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "ui/events/gesture_detection/gesture_detection_export.h"
@@ skipping 42 matching lines @@
   virtual int GetActionIndex() const = 0;
   virtual size_t GetPointerCount() const = 0;
   virtual int GetPointerId(size_t pointer_index) const = 0;
   virtual float GetX(size_t pointer_index) const = 0;
   virtual float GetY(size_t pointer_index) const = 0;
   virtual float GetRawX(size_t pointer_index) const = 0;
   virtual float GetRawY(size_t pointer_index) const = 0;
   virtual float GetTouchMajor(size_t pointer_index) const = 0;
   virtual float GetTouchMinor(size_t pointer_index) const = 0;
   virtual float GetOrientation(size_t pointer_index) const = 0;
+  virtual float GetTilt(size_t pointer_index) const = 0;

[jdduke (slow), 2015/02/20 16:20:13]

Interesting, it looks like Android repurposes orientation for stylus inputs to
convey tilt:
http://developer.android.com/reference/android/view/MotionEvent.html#AXIS_ORI....

[Rick Byers, 2015/02/20 21:19:07]

That's TiltDirection, yes.  I tried asking them if they felt conveying touch
orientation and stylus rotation with the same API (with different documentation
/ range of values for the two cases) was a good thing or a bad thing but they
just said they had no data.  Since the ranges (and likely use cases) are
different, I personally think using a separate API like this is better.  I
believe we discussed this on public-touchevents.

+  virtual float GetTiltDirection(size_t pointer_index) const = 0;
   virtual float GetPressure(size_t pointer_index) const = 0;
   virtual ToolType GetToolType(size_t pointer_index) const = 0;
   virtual int GetButtonState() const = 0;
   virtual int GetFlags() const = 0;
   virtual base::TimeTicks GetEventTime() const = 0;
 
   // Optional historical data, default implementation provides an empty history.
   virtual size_t GetHistorySize() const;
   virtual base::TimeTicks GetHistoricalEventTime(size_t historical_index) const;
   virtual float GetHistoricalTouchMajor(size_t pointer_index,
@@ skipping 14 matching lines @@
   float GetRawOffsetX() const { return GetRawX() - GetX(); }
   float GetRawOffsetY() const { return GetRawY() - GetY(); }
 
   float GetTouchMajor() const { return GetTouchMajor(0); }
   float GetTouchMinor() const { return GetTouchMinor(0); }
 
   // Returns the orientation of the major axis clockwise from vertical, in
   // radians. The return value lies in [-PI/2, PI/2].
   float GetOrientation() const { return GetOrientation(0); }
 
+  // Gets the tilt angle of the stylus away from the perpendicular to the
+  // screen. The return value lies in [0, PI/2). Default is NaN.
+  float GetTilt() const { return GetTilt(0); }
+
+  // Gets the clockwise angle from the X axis to the XY-projection of the
+  // stylus. The range is from -PI radians to PI radians. Default is NaN.
+  float GetTiltDirection() const { return GetTiltDirection(0); }
+
   float GetPressure() const { return GetPressure(0); }
   ToolType GetToolType() const { return GetToolType(0); }
 
   // O(N) search of pointers (use sparingly!). Returns -1 if |id| nonexistent.
   int FindPointerIndexOfId(int id) const;
 
   // Note that these methods perform shallow copies of the originating events.
   // They guarantee only that the returned type will reflect the same
   // data exposed by the MotionEvent interface; no guarantees are made that the
   // underlying implementation is identical to the source implementation.
   scoped_ptr<MotionEvent> Clone() const;
   scoped_ptr<MotionEvent> Cancel() const;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_H_