Add rotary encoder input source

Devices which have rotating encoders for input devices can mark
their MotionEvents as belonging to SOURCE_ROTARY_ENCODER. This is better
than mapping such input events to pre-existing input sources, which may
result is conflation regarding the expected behaviour of these older input
sources.

Events emanating from this input soruce will be accessible to the View
hierarchy via onGenericMotionEvent().

We also introduce a new axis constant, AXIS_SCROLL, for axis movements
that aren't strictly vertical or horizontal.

Bug: 18707397
Change-Id: I1ad9af7c87b97d2c98b58b71cab2b780d0c86ec3
diff --git a/core/java/android/view/InputDevice.java b/core/java/android/view/InputDevice.java
index cc4598d..5592f7a 100644
--- a/core/java/android/view/InputDevice.java
+++ b/core/java/android/view/InputDevice.java
@@ -256,6 +256,15 @@
     public static final int SOURCE_TOUCH_NAVIGATION = 0x00200000 | SOURCE_CLASS_NONE;
 
     /**
+     * The input source is a rotating encoder device whose motions should be interpreted as akin to
+     * those of a scroll wheel.
+     *
+     * @see #SOURCE_CLASS_NONE
+     * {@hide}
+     */
+    public static final int SOURCE_ROTARY_ENCODER = 0x00400000 | SOURCE_CLASS_NONE;
+
+    /**
      * The input source is a joystick.
      * (It may also be a {@link #SOURCE_GAMEPAD}).
      *
diff --git a/core/java/android/view/MotionEvent.java b/core/java/android/view/MotionEvent.java
index 6026d04..527d7e5 100644
--- a/core/java/android/view/MotionEvent.java
+++ b/core/java/android/view/MotionEvent.java
@@ -962,6 +962,22 @@
     public static final int AXIS_TILT = 25;
 
     /**
+     * Axis constant: Generic scroll axis of a motion event.
+     * <p>
+     * <ul>
+     * <li>Reports the relative movement of the generic scrolling device.
+     * </ul>
+     * </p><p>
+     * This axis should be used for scroll events that are neither strictly vertical nor horizontal.
+     * A good example would be the rotation of a rotary encoder input device.
+     * </p>
+     *
+     * @see #getAxisValue(int, int)
+     * {@hide}
+     */
+    public static final int AXIS_SCROLL = 26;
+
+    /**
      * Axis constant: Generic 1 axis of a motion event.
      * The interpretation of a generic axis is device-specific.
      *
@@ -1171,6 +1187,7 @@
         names.append(AXIS_BRAKE, "AXIS_BRAKE");
         names.append(AXIS_DISTANCE, "AXIS_DISTANCE");
         names.append(AXIS_TILT, "AXIS_TILT");
+        names.append(AXIS_SCROLL, "AXIS_SCROLL");
         names.append(AXIS_GENERIC_1, "AXIS_GENERIC_1");
         names.append(AXIS_GENERIC_2, "AXIS_GENERIC_2");
         names.append(AXIS_GENERIC_3, "AXIS_GENERIC_3");