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/*
* Copyright (C) 2022 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.window;
import android.util.FloatProperty;
import com.android.internal.dynamicanimation.animation.SpringAnimation;
import com.android.internal.dynamicanimation.animation.SpringForce;
/**
* An animator that drives the predictive back progress with a spring.
*
* The back gesture's latest touch point and committal state determines the final position of
* the spring. The continuous movement of the spring is used to produce {@link BackEvent}s with
* smoothly transitioning progress values.
*
* @hide
*/
public class BackProgressAnimator {
/**
* A factor to scale the input progress by, so that it works better with the spring.
* We divide the output progress by this value before sending it to apps, so that apps
* always receive progress values in [0, 1].
*/
private static final float SCALE_FACTOR = 100f;
private final SpringAnimation mSpring;
private ProgressCallback mCallback;
private float mProgress = 0;
private BackEvent mLastBackEvent;
private boolean mStarted = false;
private void setProgress(float progress) {
mProgress = progress;
}
private float getProgress() {
return mProgress;
}
private static final FloatProperty<BackProgressAnimator> PROGRESS_PROP =
new FloatProperty<BackProgressAnimator>("progress") {
@Override
public void setValue(BackProgressAnimator animator, float value) {
animator.setProgress(value);
animator.updateProgressValue(value);
}
@Override
public Float get(BackProgressAnimator object) {
return object.getProgress();
}
};
/** A callback to be invoked when there's a progress value update from the animator. */
public interface ProgressCallback {
/** Called when there's a progress value update. */
void onProgressUpdate(BackEvent event);
}
public BackProgressAnimator() {
mSpring = new SpringAnimation(this, PROGRESS_PROP);
mSpring.setSpring(new SpringForce()
.setStiffness(SpringForce.STIFFNESS_MEDIUM)
.setDampingRatio(SpringForce.DAMPING_RATIO_NO_BOUNCY));
}
/**
* Sets a new target position for the back progress.
*
* @param event the {@link BackEvent} containing the latest target progress.
*/
public void onBackProgressed(BackEvent event) {
if (!mStarted) {
return;
}
mLastBackEvent = event;
mSpring.animateToFinalPosition(event.getProgress() * SCALE_FACTOR);
}
/**
* Starts the back progress animation.
*
* @param event the {@link BackEvent} that started the gesture.
* @param callback the back callback to invoke for the gesture. It will receive back progress
* dispatches as the progress animation updates.
*/
public void onBackStarted(BackEvent event, ProgressCallback callback) {
reset();
mLastBackEvent = event;
mCallback = callback;
mStarted = true;
}
/**
* Resets the back progress animation. This should be called when back is invoked or cancelled.
*/
public void reset() {
mSpring.animateToFinalPosition(0);
if (mSpring.canSkipToEnd()) {
mSpring.skipToEnd();
} else {
// Should never happen.
mSpring.cancel();
}
mStarted = false;
mLastBackEvent = null;
mCallback = null;
mProgress = 0;
}
private void updateProgressValue(float progress) {
if (mLastBackEvent == null || mCallback == null || !mStarted) {
return;
}
mCallback.onProgressUpdate(
new BackEvent(mLastBackEvent.getTouchX(), mLastBackEvent.getTouchY(),
progress / SCALE_FACTOR, mLastBackEvent.getSwipeEdge(),
mLastBackEvent.getDepartingAnimationTarget()));
}
}
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