DO NOT MERGE Let BackProgressAnimator could play cancel animation

Add cancel and the cancel callback in BackProgressAnimator so it could
animate to start position and invoke the callback after finished.

Bug: 259608500
Test: atest BackAnimationControllerTest BackNavigationControllerTests
Test: atest BackProgressAnimatorTest
Change-Id: I94303ba530d155f4b264dafa21bd23185a6b44bd

core/java/android/window/BackEvent.java

@@ -99,7 +99,21 @@ public class BackEvent implements Parcelable {
     }
 
     /**
-     * Returns a value between 0 and 1 on how far along the back gesture is.
+     * Returns a value between 0 and 1 on how far along the back gesture is. This value is
+     * driven by the horizontal location of the touch point, and should be used as the fraction to
+     * seek the predictive back animation with. Specifically,
+     * <ol>
+     * <li>The progress is 0 when the touch is at the starting edge of the screen (left or right),
+     * and animation should seek to its start state.
+     * <li>The progress is approximately 1 when the touch is at the opposite side of the screen,
+     * and animation should seek to its end state. Exact end value may vary depending on
+     * screen size.
+     * </ol>
+     * <li> After the gesture finishes in cancel state, this method keeps getting invoked until the
+     * progress value animates back to 0.
+     * </ol>
+     * In-between locations are linearly interpolated based on horizontal distance from the starting
+     * edge and smooth clamped to 1 when the distance exceeds a system-wide threshold.
      */
     public float getProgress() {
         return mProgress;

core/java/android/window/BackProgressAnimator.java

@@ -16,8 +16,10 @@
 
 package android.window;
 
+import android.annotation.NonNull;
 import android.util.FloatProperty;
 
+import com.android.internal.dynamicanimation.animation.DynamicAnimation;
 import com.android.internal.dynamicanimation.animation.SpringAnimation;
 import com.android.internal.dynamicanimation.animation.SpringForce;
 
@@ -123,6 +125,27 @@ public class BackProgressAnimator {
         mProgress = 0;
     }
 
+    /**
+     * Animate the back progress animation from current progress to start position.
+     * This should be called when back is cancelled.
+     *
+     * @param finishCallback the callback to be invoked when the progress is reach to 0.
+     */
+    public void onBackCancelled(@NonNull Runnable finishCallback) {
+        final DynamicAnimation.OnAnimationEndListener listener =
+                new DynamicAnimation.OnAnimationEndListener() {
+            @Override
+            public void onAnimationEnd(DynamicAnimation animation, boolean canceled, float value,
+                    float velocity) {
+                mSpring.removeEndListener(this);
+                finishCallback.run();
+                reset();
+            }
+        };
+        mSpring.addEndListener(listener);
+        mSpring.animateToFinalPosition(0);
+    }
+
     private void updateProgressValue(float progress) {
         if (mLastBackEvent == null || mCallback == null || !mStarted) {
             return;

core/java/android/window/WindowOnBackInvokedDispatcher.java

@@ -255,12 +255,13 @@ public class WindowOnBackInvokedDispatcher implements OnBackInvokedDispatcher {
         @Override
         public void onBackCancelled() {
             Handler.getMain().post(() -> {
-                mProgressAnimator.reset();
+                mProgressAnimator.onBackCancelled(() -> {
                     final OnBackAnimationCallback callback = getBackAnimationCallback();
                     if (callback != null) {
                         callback.onBackCancelled();
                     }
                 });
+            });
         }
 
         @Override