Improve VelocityTracker numerical stability.

Replaced VelocityTracker with a faster and more accurate
native implementation.  This avoids the duplicate maintenance
overhead of having two implementations.

The new algorithm requires that the sample duration be at least
10ms in order to contribute to the velocity calculation.  This
ensures that the velocity is not severely overestimated when
samples arrive in bursts.

The new algorithm computes the exponentially weighted moving
average using weights based on the relative duration of successive
sample periods.

The new algorithm is also more careful about how it handles
individual pointers going down or up and their effects on the
collected movement traces.  The intent is to preserve the last
known velocity of pointers as they go up while also ensuring
that other motion samples do not count twice in that case.

Bug: 4086785
Change-Id: I2632321232c64d6b8faacdb929e33f60e64dcdd3

1 files changed, 7 insertions, 22 deletions

diff --git a/core/jni/android_view_MotionEvent.cpp b/core/jni/android_view_MotionEvent.cpp
index 68ebfe7..4ce471e 100644
--- a/core/jni/android_view_MotionEvent.cpp
+++ b/core/jni/android_view_MotionEvent.cpp
@@ -57,7 +57,10 @@ static struct {
 
 // ----------------------------------------------------------------------------
 
-static MotionEvent* android_view_MotionEvent_getNativePtr(JNIEnv* env, jobject eventObj) {
+MotionEvent* android_view_MotionEvent_getNativePtr(JNIEnv* env, jobject eventObj) {
+    if (!eventObj) {
+        return NULL;
+    }
     return reinterpret_cast<MotionEvent*>(
             env->GetIntField(eventObj, gMotionEventClassInfo.mNativePtr));
 }
@@ -68,10 +71,10 @@ static void android_view_MotionEvent_setNativePtr(JNIEnv* env, jobject eventObj,
             reinterpret_cast<int>(event));
 }
 
-jobject android_view_MotionEvent_fromNative(JNIEnv* env, const MotionEvent* event) {
+jobject android_view_MotionEvent_obtainAsCopy(JNIEnv* env, const MotionEvent* event) {
     jobject eventObj = env->CallStaticObjectMethod(gMotionEventClassInfo.clazz,
             gMotionEventClassInfo.obtain);
-    if (env->ExceptionCheck()) {
+    if (env->ExceptionCheck() || !eventObj) {
         LOGE("An exception occurred while obtaining a motion event.");
         LOGE_EX(env);
         env->ExceptionClear();
@@ -88,18 +91,6 @@ jobject android_view_MotionEvent_fromNative(JNIEnv* env, const MotionEvent* even
     return eventObj;
 }
 
-status_t android_view_MotionEvent_toNative(JNIEnv* env, jobject eventObj,
-        MotionEvent* event) {
-    MotionEvent* srcEvent = android_view_MotionEvent_getNativePtr(env, eventObj);
-    if (!srcEvent) {
-        LOGE("MotionEvent was finalized");
-        return BAD_VALUE;
-    }
-
-    event->copyFrom(srcEvent, true);
-    return OK;
-}
-
 status_t android_view_MotionEvent_recycle(JNIEnv* env, jobject eventObj) {
     env->CallVoidMethod(eventObj, gMotionEventClassInfo.recycle);
     if (env->ExceptionCheck()) {
@@ -500,13 +491,7 @@ static jint android_view_MotionEvent_nativeGetPointerId(JNIEnv* env, jclass claz
 static jint android_view_MotionEvent_nativeFindPointerIndex(JNIEnv* env, jclass clazz,
         jint nativePtr, jint pointerId) {
     MotionEvent* event = reinterpret_cast<MotionEvent*>(nativePtr);
-    size_t pointerCount = event->getPointerCount();
-    for (size_t i = 0; i < pointerCount; i++) {
-        if (event->getPointerId(i) == pointerId) {
-            return i;
-        }
-    }
-    return -1;
+    return jint(event->findPointerIndex(pointerId));
 }
 
 static jint android_view_MotionEvent_nativeGetHistorySize(JNIEnv* env, jclass clazz,