Improve fling physics for recents

- Don't limit swipe out velocity
- Make sure we pick up all touch events in VelocityTracker
- When already scrolling and touching again, don't reset scroll
  state, so we don't wait for the touch slop again to start
  scrolling (this makes it more consistent with ScrollView).

Bug: 18536759
Change-Id: I1d43c77db78beec6d0b8c949e67141a2665de892

2 files changed, 7 insertions, 16 deletions

diff --git a/packages/SystemUI/src/com/android/systemui/recents/views/SwipeHelper.java b/packages/SystemUI/src/com/android/systemui/recents/views/SwipeHelper.java
index fa44551..0428b48 100644
--- a/packages/SystemUI/src/com/android/systemui/recents/views/SwipeHelper.java
+++ b/packages/SystemUI/src/com/android/systemui/recents/views/SwipeHelper.java
@@ -50,7 +50,6 @@ public class SwipeHelper {
     private float SWIPE_ESCAPE_VELOCITY = 100f; // dp/sec
     private int DEFAULT_ESCAPE_ANIMATION_DURATION = 75; // ms
     private int MAX_ESCAPE_ANIMATION_DURATION = 150; // ms
-    private int MAX_DISMISS_VELOCITY = 2000; // dp/sec
     private static final int SNAP_ANIM_LEN = SLOW_ANIMATIONS ? 1000 : 250; // ms
 
     public static float ALPHA_FADE_START = 0.15f; // fraction of thumbnail width
@@ -350,8 +349,7 @@ public class SwipeHelper {
     }
 
     private void endSwipe(VelocityTracker velocityTracker) {
-        float maxVelocity = MAX_DISMISS_VELOCITY * mDensityScale;
-        velocityTracker.computeCurrentVelocity(1000 /* px/sec */, maxVelocity);
+        velocityTracker.computeCurrentVelocity(1000 /* px/sec */);
         float velocity = getVelocity(velocityTracker);
         float perpendicularVelocity = getPerpendicularVelocity(velocityTracker);
         float escapeVelocity = SWIPE_ESCAPE_VELOCITY * mDensityScale;
diff --git a/packages/SystemUI/src/com/android/systemui/recents/views/TaskStackViewTouchHandler.java b/packages/SystemUI/src/com/android/systemui/recents/views/TaskStackViewTouchHandler.java
index 2b173a9..c59f82c 100644
--- a/packages/SystemUI/src/com/android/systemui/recents/views/TaskStackViewTouchHandler.java
+++ b/packages/SystemUI/src/com/android/systemui/recents/views/TaskStackViewTouchHandler.java
@@ -143,22 +143,21 @@ class TaskStackViewTouchHandler implements SwipeHelper.Callback {
                 // Initialize the velocity tracker
                 initOrResetVelocityTracker();
                 mVelocityTracker.addMovement(createMotionEventForStackScroll(ev));
-                // Check if the scroller is finished yet
-                mIsScrolling = mScroller.isScrolling();
                 break;
             }
             case MotionEvent.ACTION_MOVE: {
                 if (mActivePointerId == INACTIVE_POINTER_ID) break;
 
+                // Initialize the velocity tracker if necessary
+                initVelocityTrackerIfNotExists();
+                mVelocityTracker.addMovement(createMotionEventForStackScroll(ev));
+
                 int activePointerIndex = ev.findPointerIndex(mActivePointerId);
                 int y = (int) ev.getY(activePointerIndex);
                 int x = (int) ev.getX(activePointerIndex);
                 if (Math.abs(y - mInitialMotionY) > mScrollTouchSlop) {
                     // Save the touch move info
                     mIsScrolling = true;
-                    // Initialize the velocity tracker if necessary
-                    initVelocityTrackerIfNotExists();
-                    mVelocityTracker.addMovement(createMotionEventForStackScroll(ev));
                     // Disallow parents from intercepting touch events
                     final ViewParent parent = mSv.getParent();
                     if (parent != null) {
@@ -237,6 +236,8 @@ class TaskStackViewTouchHandler implements SwipeHelper.Callback {
             case MotionEvent.ACTION_MOVE: {
                 if (mActivePointerId == INACTIVE_POINTER_ID) break;
 
+                mVelocityTracker.addMovement(createMotionEventForStackScroll(ev));
+
                 int activePointerIndex = ev.findPointerIndex(mActivePointerId);
                 int x = (int) ev.getX(activePointerIndex);
                 int y = (int) ev.getY(activePointerIndex);
@@ -246,9 +247,6 @@ class TaskStackViewTouchHandler implements SwipeHelper.Callback {
                 if (!mIsScrolling) {
                     if (yTotal > mScrollTouchSlop) {
                         mIsScrolling = true;
-                        // Initialize the velocity tracker
-                        initOrResetVelocityTracker();
-                        mVelocityTracker.addMovement(createMotionEventForStackScroll(ev));
                         // Disallow parents from intercepting touch events
                         final ViewParent parent = mSv.getParent();
                         if (parent != null) {
@@ -267,11 +265,6 @@ class TaskStackViewTouchHandler implements SwipeHelper.Callback {
                                 / maxOverScroll));
                     }
                     mScroller.setStackScroll(curStackScroll + deltaP);
-                    if (mScroller.isScrollOutOfBounds()) {
-                        mVelocityTracker.clear();
-                    } else {
-                        mVelocityTracker.addMovement(createMotionEventForStackScroll(ev));
-                    }
                 }
                 mLastMotionX = x;
                 mLastMotionY = y;