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

ui/events/gesture_detection/motion_event.h

Index: ui/events/gesture_detection/motion_event.h
diff --git a/ui/events/gesture_detection/motion_event.h b/ui/events/gesture_detection/motion_event.h
index 560afcbd044c20155ed281e7762f33ddbba77bb7..770a2290d0c3bd9ddaea295584e8338f62a567bb 100644
--- a/ui/events/gesture_detection/motion_event.h
+++ b/ui/events/gesture_detection/motion_event.h
@@ -60,6 +60,8 @@ class GESTURE_DETECTION_EXPORT MotionEvent {
   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;
@@ -94,6 +96,14 @@ class GESTURE_DETECTION_EXPORT MotionEvent {
   // 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); }