1 files changed, 141 insertions, 0 deletions
diff --git a/quickstep/src/com/android/quickstep/util/MotionPauseDetector.java b/quickstep/src/com/android/quickstep/util/MotionPauseDetector.java
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index 000000000..258e9227e
--- /dev/null
+++ b/quickstep/src/com/android/quickstep/util/MotionPauseDetector.java
@@ -0,0 +1,141 @@
+/*
+ * Copyright (C) 2019 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 com.android.quickstep.util;
+
+import android.content.Context;
+import android.content.res.Resources;
+import android.os.SystemClock;
+import android.view.MotionEvent;
+
+import com.android.launcher3.R;
+
+/**
+ * Given positions along x- or y-axis, tracks velocity and acceleration and determines when there is
+ * a pause in motion.
+ */
+public class MotionPauseDetector {
+
+    // The percentage of the previous speed that determines whether this is a rapid deceleration.
+    // The bigger this number, the easier it is to trigger the first pause.
+    private static final float RAPID_DECELERATION_FACTOR = 0.6f;
+
+    private final float mSpeedVerySlow;
+    private final float mSpeedSomewhatFast;
+    private final float mSpeedFast;
+    private final float mMinDisplacementForPause;
+
+    private Long mPreviousTime = null;
+    private Float mPreviousPosition = null;
+    private Float mPreviousVelocity = null;
+
+    private Float mFirstPosition = null;
+
+    private OnMotionPauseListener mOnMotionPauseListener;
+    private boolean mIsPaused;
+    // Bias more for the first pause to make it feel extra responsive.
+    private boolean mHasEverBeenPaused;
+
+    public MotionPauseDetector(Context context) {
+        Resources res = context.getResources();
+        mSpeedVerySlow = res.getDimension(R.dimen.motion_pause_detector_speed_very_slow);
+        mSpeedSomewhatFast = res.getDimension(R.dimen.motion_pause_detector_speed_somewhat_fast);
+        mSpeedFast = res.getDimension(R.dimen.motion_pause_detector_speed_fast);
+        mMinDisplacementForPause = res.getDimension(R.dimen.motion_pause_detector_min_displacement);
+    }
+
+    /**
+     * Get callbacks for when motion pauses and resumes, including an
+     * immediate callback with the current pause state.
+     */
+    public void setOnMotionPauseListener(OnMotionPauseListener listener) {
+        mOnMotionPauseListener = listener;
+        if (mOnMotionPauseListener != null) {
+            mOnMotionPauseListener.onMotionPauseChanged(mIsPaused);
+        }
+    }
+
+    /**
+     * Computes velocity and acceleration to determine whether the motion is paused.
+     * @param position The x or y component of the motion being tracked.
+     *
+     * TODO: Use historical positions as well, e.g. {@link MotionEvent#getHistoricalY(int, int)}.
+     */
+    public void addPosition(float position) {
+        if (mFirstPosition == null) {
+            mFirstPosition = position;
+        }
+        long time = SystemClock.uptimeMillis();
+        if (mPreviousTime != null && mPreviousPosition != null) {
+            long changeInTime = Math.max(1, time - mPreviousTime);
+            float changeInPosition = position - mPreviousPosition;
+            float velocity = changeInPosition / changeInTime;
+            if (mPreviousVelocity != null) {
+                checkMotionPaused(velocity, mPreviousVelocity, Math.abs(position - mFirstPosition));
+            }
+            mPreviousVelocity = velocity;
+        }
+        mPreviousTime = time;
+        mPreviousPosition = position;
+    }
+
+    private void checkMotionPaused(float velocity, float prevVelocity, float totalDisplacement) {
+        float speed = Math.abs(velocity);
+        float previousSpeed = Math.abs(prevVelocity);
+        boolean isPaused;
+        if (mIsPaused) {
+            // Continue to be paused until moving at a fast speed.
+            isPaused = speed < mSpeedFast || previousSpeed < mSpeedFast;
+        } else {
+            if (velocity < 0 != prevVelocity < 0) {
+                // We're just changing directions, not necessarily stopping.
+                isPaused = false;
+            } else {
+                isPaused = speed < mSpeedVerySlow && previousSpeed < mSpeedVerySlow;
+                if (!isPaused && !mHasEverBeenPaused) {
+                    // We want to be more aggressive about detecting the first pause to ensure it
+                    // feels as responsive as possible; getting two very slow speeds back to back
+                    // takes too long, so also check for a rapid deceleration.
+                    boolean isRapidDeceleration = speed < previousSpeed * RAPID_DECELERATION_FACTOR;
+                    isPaused = isRapidDeceleration && speed < mSpeedSomewhatFast;
+                }
+            }
+        }
+        boolean passedMinDisplacement = totalDisplacement >= mMinDisplacementForPause;
+        isPaused &= passedMinDisplacement;
+        if (mIsPaused != isPaused) {
+            mIsPaused = isPaused;
+            if (mIsPaused) {
+                mHasEverBeenPaused = true;
+            }
+            if (mOnMotionPauseListener != null) {
+                mOnMotionPauseListener.onMotionPauseChanged(mIsPaused);
+            }
+        }
+    }
+
+    public void clear() {
+        mPreviousTime = null;
+        mPreviousPosition = null;
+        mPreviousVelocity = null;
+        mFirstPosition = null;
+        setOnMotionPauseListener(null);
+        mIsPaused = mHasEverBeenPaused = false;
+    }
+
+    public interface OnMotionPauseListener {
+        void onMotionPauseChanged(boolean isPaused);
+    }
+}