Change mechanism to prevent backwards prediction
Under specific circumstances it was possible to have very large
predictions; the root cause is an unfortunate interaction between
the prediction ratchet not capping prediction in the future, and
the prediction event time being computed incorrectly.
This change will correct both of these issues: the prediction will
now not go beyond the previous one unless specifically requested,
and the event time calculation is now more accurate.
Bug: 369330439
Test: gradlew :input:input-motionprediction:test
Change-Id: Ifbf492418e3a15ff4743526a394c2da7c3941268
diff --git a/input/input-motionprediction/src/main/java/androidx/input/motionprediction/kalman/SinglePointerPredictor.java b/input/input-motionprediction/src/main/java/androidx/input/motionprediction/kalman/SinglePointerPredictor.java
index 5ad7111..0d7627e 100644
--- a/input/input-motionprediction/src/main/java/androidx/input/motionprediction/kalman/SinglePointerPredictor.java
+++ b/input/input-motionprediction/src/main/java/androidx/input/motionprediction/kalman/SinglePointerPredictor.java
@@ -72,11 +72,11 @@
private final DVector2 mLastPosition = new DVector2();
private long mLastSeenEventTime;
- private long mLastPredictEventTime;
+ private double mLastPredictEventTime;
private long mDownEventTime;
- private List<Float> mReportRates = new LinkedList<>();
+ private List<Double> mReportRates = new LinkedList<>();
private int mExpectedPredictionSampleSize = -1;
- private float mReportRateMs = 0;
+ private double mReportRateMs = 0;
private final DVector2 mPosition = new DVector2();
private final DVector2 mVelocity = new DVector2();
@@ -141,10 +141,10 @@
// to be used as an estimate.
if (mReportRates != null && mReportRates.size() < 20) {
if (mLastSeenEventTime > 0) {
- float dt = eventTime - mLastSeenEventTime;
+ double dt = eventTime - mLastSeenEventTime;
mReportRates.add(dt);
- float sum = 0;
- for (float rate : mReportRates) {
+ double sum = 0;
+ for (double rate : mReportRates) {
sum += rate;
}
mReportRateMs = sum / mReportRates.size();
@@ -250,16 +250,6 @@
int predictionTargetInSamples =
(int) Math.ceil(predictionTargetMs / mReportRateMs * confidenceFactor);
- // Predict at least as far in time as the previous prediction.
- // Otherwise, it may appear that the coordinates are going backwards.
- if (mLastPredictEventTime > mLastSeenEventTime) {
- int minimumPredictionSampleSize = (int) Math.floor(
- (mLastPredictEventTime - mLastSeenEventTime) / mReportRateMs
- );
- if (predictionTargetInSamples < minimumPredictionSampleSize) {
- predictionTargetInSamples = minimumPredictionSampleSize;
- }
- }
if (mExpectedPredictionSampleSize != -1) {
// Normally this should always be false as confidenceFactor should be less than 1.0
if (predictionTargetInSamples > mExpectedPredictionSampleSize) {
@@ -272,9 +262,11 @@
predictionTargetInSamples = Math.max(predictionTargetInSamples, 1);
}
- long predictedEventTime = mLastSeenEventTime;
- int i = 0;
- for (; i < predictionTargetInSamples; i++) {
+ double predictedEventTime = mLastSeenEventTime;
+ double nextPredictedEventTime = mLastSeenEventTime + mReportRateMs;
+ for (int i = 0;
+ i < predictionTargetInSamples || (nextPredictedEventTime <= mLastPredictEventTime);
+ i++) {
mAcceleration.a1 += mJank.a1 * JANK_INFLUENCE;
mAcceleration.a2 += mJank.a2 * JANK_INFLUENCE;
mVelocity.a1 += mAcceleration.a1 * ACCELERATION_INFLUENCE;
@@ -290,8 +282,6 @@
mPressure = 1;
}
- long nextPredictedEventTime = predictedEventTime + Math.round(mReportRateMs);
-
// Abort prediction if the pen is to be lifted.
if (mPredictLift
&& mPressure < 0.1
@@ -310,7 +300,7 @@
predictedEvent =
MotionEvent.obtain(
mDownEventTime /* downTime */,
- nextPredictedEventTime /* eventTime */,
+ (long) nextPredictedEventTime /* eventTime */,
MotionEvent.ACTION_MOVE /* action */,
1 /* pointerCount */,
pointerProperties /* pointer properties */,
@@ -324,9 +314,13 @@
0 /* source */,
0 /* flags */);
} else {
- predictedEvent.addBatch(nextPredictedEventTime, coords, 0);
+ predictedEvent.addBatch((long) nextPredictedEventTime, coords, 0);
}
+ // Keep track of the last predicted time
predictedEventTime = nextPredictedEventTime;
+
+ // Prepare for next iteration
+ nextPredictedEventTime += mReportRateMs;
}
// Store the last predicted time
