diff --git a/res/values/dimens.xml b/res/values/dimens.xml
index cda8c05..02c6c70 100644
--- a/res/values/dimens.xml
+++ b/res/values/dimens.xml
@@ -88,6 +88,7 @@
     <dimen name="all_apps_search_bar_bg_overflow">-6dp</dimen>
     <dimen name="all_apps_search_bar_divider_width">1dp</dimen>
 
+    <dimen name="all_apps_bezel_swipe_height">24dp</dimen>
 <!-- Widget tray -->
     <dimen name="widget_preview_label_vertical_padding">8dp</dimen>
     <dimen name="widget_preview_label_horizontal_padding">8dp</dimen>
diff --git a/src/com/android/launcher3/LauncherStateTransitionAnimation.java b/src/com/android/launcher3/LauncherStateTransitionAnimation.java
index fd4aff9..e94153d 100644
--- a/src/com/android/launcher3/LauncherStateTransitionAnimation.java
+++ b/src/com/android/launcher3/LauncherStateTransitionAnimation.java
@@ -420,7 +420,7 @@
                       pCb.onTransitionComplete();
                   }
             });
-            mAllAppsController.animateToAllApps(animation, revealDuration);
+            mAllAppsController.animateToAllApps(animation, revealDuration, false);
 
             dispatchOnLauncherTransitionPrepare(fromView, animated, false);
             dispatchOnLauncherTransitionPrepare(toView, animated, false);
@@ -861,37 +861,31 @@
             return animation;
         } else if (animType == PULLUP) {
             animation.addListener(new AnimatorListenerAdapter() {
+                boolean canceled = false;
                 @Override
-                public void onAnimationEnd(Animator animation) {
-                    dispatchOnLauncherTransitionEnd(fromView, animated, false);
-                    dispatchOnLauncherTransitionEnd(toView, animated, false);
-                    cleanupAnimation();
-                    pCb.onTransitionComplete();
+                public void onAnimationCancel(Animator animation) {
+                    canceled = true;
                 }
 
-            });
-            mAllAppsController.animateToWorkspace(animation, revealDuration);
-
-            // Dispatch the prepare transition signal
-            dispatchOnLauncherTransitionPrepare(fromView, animated, false);
-            dispatchOnLauncherTransitionPrepare(toView, animated, false);
-
-            animation.addListener(new AnimatorListenerAdapter() {
                 @Override
                 public void onAnimationEnd(Animator animation) {
-                    dispatchOnLauncherTransitionEnd(fromView, animated, true);
-                    dispatchOnLauncherTransitionEnd(toView, animated, true);
-
+                    if (canceled) return;
+                    dispatchOnLauncherTransitionEnd(fromView, animated, false);
+                    dispatchOnLauncherTransitionEnd(toView, animated, false);
                     // Run any queued runnables
                     if (onCompleteRunnable != null) {
                         onCompleteRunnable.run();
                     }
-
-                    // This can hold unnecessary references to views.
                     cleanupAnimation();
                     pCb.onTransitionComplete();
                 }
+
             });
+            mAllAppsController.animateToWorkspace(animation, revealDuration, false);
+
+            // Dispatch the prepare transition signal
+            dispatchOnLauncherTransitionPrepare(fromView, animated, false);
+            dispatchOnLauncherTransitionPrepare(toView, animated, false);
 
             final AnimatorSet stateAnimation = animation;
             final Runnable startAnimRunnable = new Runnable() {
diff --git a/src/com/android/launcher3/WorkspaceStateTransitionAnimation.java b/src/com/android/launcher3/WorkspaceStateTransitionAnimation.java
index bd71808..888cc57 100644
--- a/src/com/android/launcher3/WorkspaceStateTransitionAnimation.java
+++ b/src/com/android/launcher3/WorkspaceStateTransitionAnimation.java
@@ -30,6 +30,7 @@
 import android.view.accessibility.AccessibilityNodeInfo;
 import android.view.animation.DecelerateInterpolator;
 
+import com.android.launcher3.config.FeatureFlags;
 import com.android.launcher3.dragndrop.DragLayer;
 import com.android.launcher3.util.Thunk;
 
@@ -43,6 +44,7 @@
 
     private View mView;
     private boolean mAccessibilityEnabled;
+    private boolean mCanceled = false;
 
     public AlphaUpdateListener(View v, boolean accessibilityEnabled) {
         mView = v;
@@ -67,7 +69,13 @@
     }
 
     @Override
+    public void onAnimationCancel(Animator animation) {
+        mCanceled = true;
+    }
+
+    @Override
     public void onAnimationEnd(Animator arg0) {
+        if (mCanceled) return;
         updateVisibility(mView, mAccessibilityEnabled);
     }
 
@@ -322,8 +330,10 @@
             boolean isCurrentPage = (i == toPage);
             float initialAlpha = cl.getShortcutsAndWidgets().getAlpha();
             float finalAlpha;
-            if (states.stateIsNormalHidden || states.stateIsOverviewHidden) {
+            if (states.stateIsOverviewHidden) {
                 finalAlpha = 0f;
+            } else if(states.stateIsNormalHidden) {
+                finalAlpha = FeatureFlags.LAUNCHER3_ALL_APPS_PULL_UP  ? 1 : 0;
             } else if (states.stateIsNormal && mWorkspaceFadeInAdjacentScreens) {
                 finalAlpha = (i == toPage || i < customPageCount) ? 1f : 0f;
             } else {
@@ -447,10 +457,16 @@
             mStateAnimator.play(hotseatAlpha);
             mStateAnimator.play(pageIndicatorAlpha);
             mStateAnimator.addListener(new AnimatorListenerAdapter() {
+                boolean canceled = false;
+                @Override
+                public void onAnimationCancel(Animator animation) {
+                    canceled = true;
+                }
+
                 @Override
                 public void onAnimationEnd(Animator animation) {
                     mStateAnimator = null;
-
+                    if (canceled) return;
                     if (accessibilityEnabled && overviewPanel.getVisibility() == View.VISIBLE) {
                         overviewPanel.getChildAt(0).performAccessibilityAction(
                                 AccessibilityNodeInfo.ACTION_ACCESSIBILITY_FOCUS, null);
diff --git a/src/com/android/launcher3/allapps/AllAppsTransitionController.java b/src/com/android/launcher3/allapps/AllAppsTransitionController.java
index f30e08e..3157c13 100644
--- a/src/com/android/launcher3/allapps/AllAppsTransitionController.java
+++ b/src/com/android/launcher3/allapps/AllAppsTransitionController.java
@@ -17,6 +17,7 @@
 import com.android.launcher3.Launcher;
 import com.android.launcher3.LauncherAnimUtils;
 import com.android.launcher3.PagedView;
+import com.android.launcher3.R;
 import com.android.launcher3.Workspace;
 import com.android.launcher3.Workspace.Direction;
 import com.android.launcher3.util.TouchController;
@@ -39,8 +40,8 @@
     private final Interpolator mAccelInterpolator = new AccelerateInterpolator(2f);
     private final Interpolator mDecelInterpolator = new DecelerateInterpolator(1f);
 
-    private static final float ANIMATION_DURATION = 2000;
-    public static final float ALL_APPS_FINAL_ALPHA = .8f;
+    private static final float ANIMATION_DURATION = 1200;
+    public static final float ALL_APPS_FINAL_ALPHA = .9f;
 
     private static final float PARALLAX_COEFFICIENT = .125f;
 
@@ -54,33 +55,34 @@
     private final Launcher mLauncher;
     private final VerticalPullDetector mDetector;
 
-    // Animation in this class is controlled by a single variable {@link mProgressTransY}.
+    // Animation in this class is controlled by a single variable {@link mShiftCurrent}.
     // Visually, it represents top y coordinate of the all apps container. Using the
-    // {@link mTranslation} as the denominator, this fraction value ranges in [0, 1].
-    private float mProgressTransY;   // numerator
-    private float mTranslation = -1; // denominator
+    // {@link mShiftRange} as the denominator, this fraction value ranges in [0, 1].
+    //
+    // When {@link mShiftCurrent} is 0, all apps container is pulled up.
+    // When {@link mShiftCurrent} is {@link mShirtRange}, all apps container is pulled down.
+    private float mShiftStart;      // [0, mShiftRange]
+    private float mShiftCurrent;    // [0, mShiftRange]
+    private float mShiftRange;      // changes depending on the orientation
+
 
     private static final float RECATCH_REJECTION_FRACTION = .0875f;
 
-    // Used in landscape.
-    private static final float BAZEL_PULL_UP_HEIGHT = 60;
-
+    private int mBezelSwipeUpHeight;
     private long mAnimationDuration;
-    private float mCurY;
+
 
     private AnimatorSet mCurrentAnimation;
     private boolean mNoIntercept;
 
     private boolean mLightStatusBar;
 
-    // At the end of scroll settling, this class also sets the state of the launcher.
-    // If it's already set,do not call the #mLauncher.setXXX method.
-    private boolean mStateAlreadyChanged;
-
     public AllAppsTransitionController(Launcher launcher) {
         mLauncher = launcher;
         mDetector = new VerticalPullDetector(launcher);
         mDetector.setListener(this);
+        mBezelSwipeUpHeight = launcher.getResources().getDimensionPixelSize(
+                R.dimen.all_apps_bezel_swipe_height);
     }
 
     @Override
@@ -95,26 +97,49 @@
             } else if (!mLauncher.isAllAppsVisible() && !shouldPossiblyIntercept(ev)) {
                 mNoIntercept = true;
             } else {
-                mDetector.setDetectableScrollConditions(mLauncher.isAllAppsVisible() /* down */,
-                        isInDisallowRecatchTopZone(), isInDisallowRecatchBottomZone());
+                // Now figure out which direction scroll events the controller will start
+                // calling the callbacks.
+                int conditionsToReportScroll = 0;
+
+                if (mDetector.isRestingState()) {
+                    if (mLauncher.isAllAppsVisible()) {
+                        conditionsToReportScroll |= VerticalPullDetector.THRESHOLD_DOWN;
+                    } else {
+                        conditionsToReportScroll |= VerticalPullDetector.THRESHOLD_UP;
+                    }
+                } else {
+                    if (isInDisallowRecatchBottomZone()) {
+                        conditionsToReportScroll |= VerticalPullDetector.THRESHOLD_UP;
+                    } else if (isInDisallowRecatchTopZone()) {
+                        conditionsToReportScroll |= VerticalPullDetector.THRESHOLD_DOWN;
+                    } else {
+                        conditionsToReportScroll |= VerticalPullDetector.THRESHOLD_ONLY;
+                    }
+                }
+                mDetector.setDetectableScrollConditions(conditionsToReportScroll);
             }
         }
         if (mNoIntercept) {
             return false;
         }
         mDetector.onTouchEvent(ev);
+        if (mDetector.isScrollingState() && (isInDisallowRecatchBottomZone() || isInDisallowRecatchTopZone())) {
+            return false;
+        }
         return mDetector.shouldIntercept();
     }
 
     private boolean shouldPossiblyIntercept(MotionEvent ev) {
         DeviceProfile grid = mLauncher.getDeviceProfile();
         if (mDetector.isRestingState()) {
-            if (mLauncher.getDragLayer().isEventOverHotseat(ev) && !grid.isLandscape) {
-                return true;
-            }
-            if (ev.getY() > mLauncher.getDeviceProfile().heightPx - BAZEL_PULL_UP_HEIGHT &&
-                    grid.isLandscape) {
-                return true;
+            if (grid.isVerticalBarLayout()) {
+                if (ev.getY() > mLauncher.getDeviceProfile().heightPx - mBezelSwipeUpHeight) {
+                    return true;
+                }
+            } else {
+                if (mLauncher.getDragLayer().isEventOverHotseat(ev) && !grid.isVerticalBarLayout()) {
+                    return true;
+                }
             }
             return false;
         } else {
@@ -128,32 +153,92 @@
     }
 
     private boolean isInDisallowRecatchTopZone() {
-        return mProgressTransY / mTranslation < RECATCH_REJECTION_FRACTION;
+        return mShiftCurrent / mShiftRange < RECATCH_REJECTION_FRACTION;
     }
 
     private boolean isInDisallowRecatchBottomZone() {
-        return mProgressTransY / mTranslation > 1 - RECATCH_REJECTION_FRACTION;
+        return mShiftCurrent / mShiftRange > 1 - RECATCH_REJECTION_FRACTION;
     }
 
     @Override
     public void onScrollStart(boolean start) {
         cancelAnimation();
         mCurrentAnimation = LauncherAnimUtils.createAnimatorSet();
+        mShiftStart = mAppsView.getTranslationY();
         preparePull(start);
     }
 
+    @Override
+    public boolean onScroll(float displacement, float velocity) {
+        if (mAppsView == null) {
+            return false;   // early termination.
+        }
+        if (0 <= mShiftStart + displacement && mShiftStart + displacement < mShiftRange) {
+            setProgress(mShiftStart + displacement);
+        }
+        return true;
+    }
+
+    @Override
+    public void onScrollEnd(float velocity, boolean fling) {
+        if (mAppsView == null) {
+            return; // early termination.
+        }
+
+        if (fling) {
+            if (velocity < 0) {
+                calculateDuration(velocity, mAppsView.getTranslationY());
+
+                if (!mLauncher.isAllAppsVisible()) {
+                    mLauncher.showAppsView(true, true, false, false);
+                } else {
+                    animateToAllApps(mCurrentAnimation, mAnimationDuration, true);
+                }
+            } else {
+                calculateDuration(velocity, Math.abs(mShiftRange - mAppsView.getTranslationY()));
+                if (mLauncher.isAllAppsVisible()) {
+                    mLauncher.showWorkspace(true);
+                } else {
+                    animateToWorkspace(mCurrentAnimation, mAnimationDuration, true);
+                }
+            }
+            // snap to top or bottom using the release velocity
+        } else {
+            if (mAppsView.getTranslationY() > mShiftRange / 2) {
+                calculateDuration(velocity, Math.abs(mShiftRange - mAppsView.getTranslationY()));
+                if (mLauncher.isAllAppsVisible()) {
+                    mLauncher.showWorkspace(true);
+                } else {
+                    animateToWorkspace(mCurrentAnimation, mAnimationDuration, true);
+                }
+            } else {
+                calculateDuration(velocity, Math.abs(mAppsView.getTranslationY()));
+                if (!mLauncher.isAllAppsVisible()) {
+                    mLauncher.showAppsView(true, true, false, false);
+                } else {
+                    animateToAllApps(mCurrentAnimation, mAnimationDuration, true);
+                }
+
+            }
+        }
+    }
     /**
      * @param start {@code true} if start of new drag.
      */
     public void preparePull(boolean start) {
-        // Initialize values that should not change until #onScrollEnd
-        mCurY = mAppsView.getTranslationY();
-        mStatusBarHeight = mLauncher.getDragLayer().getInsets().top;
-        mHotseat.setVisibility(View.VISIBLE);
-        mHotseat.bringToFront();
         if (start) {
+            // Initialize values that should not change until #onScrollEnd
+            mStatusBarHeight = mLauncher.getDragLayer().getInsets().top;
+            mHotseat.setVisibility(View.VISIBLE);
+            mHotseat.bringToFront();
+            if (!mLauncher.getDeviceProfile().isVerticalBarLayout()) {
+                mShiftRange = mHotseat.getTop();
+            } else {
+                mShiftRange = mHotseat.getBottom();
+            }
             if (!mLauncher.isAllAppsVisible()) {
                 mLauncher.tryAndUpdatePredictedApps();
+
                 mHotseatBackgroundAlpha = mHotseat.getBackground().getAlpha() / 255f;
                 mHotseat.setBackgroundTransparent(true /* transparent */);
                 mAppsView.setVisibility(View.VISIBLE);
@@ -163,12 +248,13 @@
                 mAppsView.getRevealView().setAlpha(mHotseatBackgroundAlpha);
 
                 DeviceProfile grid= mLauncher.getDeviceProfile();
-                if (!grid.isLandscape) {
-                    mTranslation = mHotseat.getTop();
+                if (!grid.isVerticalBarLayout()) {
+                    mShiftRange = mHotseat.getTop();
                 } else {
-                    mTranslation = mHotseat.getBottom();
+                    mShiftRange = mHotseat.getBottom();
                 }
-                setProgress(mTranslation);
+                mAppsView.getRevealView().setAlpha(mHotseatBackgroundAlpha);
+                setProgress(mShiftRange);
             } else {
                 // TODO: get rid of this workaround to override state change by workspace transition
                 mWorkspace.onLauncherTransitionPrepare(mLauncher, false, false);
@@ -177,6 +263,8 @@
                 child.setVisibility(View.VISIBLE);
                 child.setAlpha(1f);
             }
+        } else {
+            setProgress(mShiftCurrent);
         }
     }
 
@@ -199,23 +287,12 @@
         mLightStatusBar = enable;
     }
 
-    @Override
-    public boolean onScroll(float displacement, float velocity) {
-        if (mAppsView == null) {
-            return false;   // early termination.
-        }
-        if (0 <= mCurY + displacement && mCurY + displacement < mTranslation) {
-            setProgress(mCurY + displacement);
-        }
-        return true;
-    }
-
     /**
      * @param progress y value of the border between hotseat and all apps
      */
     public void setProgress(float progress) {
         updateLightStatusBar(progress);
-        mProgressTransY = progress;
+        mShiftCurrent = progress;
         float alpha = calcAlphaAllApps(progress);
         float workspaceHotseatAlpha = 1 - alpha;
 
@@ -224,67 +301,45 @@
         mAppsView.getContentView().setAlpha(alpha);
         mAppsView.setTranslationY(progress);
         mWorkspace.setWorkspaceTranslation(Direction.Y,
-                PARALLAX_COEFFICIENT *(-mTranslation + progress),
+                PARALLAX_COEFFICIENT * (-mShiftRange + progress),
                 mAccelInterpolator.getInterpolation(workspaceHotseatAlpha));
-        mWorkspace.setHotseatTranslation(Direction.Y, -mTranslation + progress,
-                mAccelInterpolator.getInterpolation(workspaceHotseatAlpha));
+        if (!mLauncher.getDeviceProfile().isVerticalBarLayout()) {
+            mWorkspace.setHotseatTranslation(Direction.Y, -mShiftRange + progress,
+                    mAccelInterpolator.getInterpolation(workspaceHotseatAlpha));
+        } else {
+            mWorkspace.setHotseatTranslation(Direction.Y,
+                    PARALLAX_COEFFICIENT * (-mShiftRange + progress),
+                    mAccelInterpolator.getInterpolation(workspaceHotseatAlpha));
+        }
     }
 
     public float getProgress() {
-        return mProgressTransY;
+        return mShiftCurrent;
     }
 
     private float calcAlphaAllApps(float progress) {
-        return ((mTranslation - progress)/mTranslation);
-    }
-
-    @Override
-    public void onScrollEnd(float velocity, boolean fling) {
-        if (mAppsView == null) {
-            return; // early termination.
-        }
-
-        if (fling) {
-            if (velocity < 0) {
-                calculateDuration(velocity, mAppsView.getTranslationY());
-                animateToAllApps(mCurrentAnimation, mAnimationDuration);
-            } else {
-                calculateDuration(velocity, Math.abs(mTranslation - mAppsView.getTranslationY()));
-                animateToWorkspace(mCurrentAnimation, mAnimationDuration);
-            }
-            // snap to top or bottom using the release velocity
-        } else {
-            if (mAppsView.getTranslationY() > mTranslation / 2) {
-                calculateDuration(velocity, Math.abs(mTranslation - mAppsView.getTranslationY()));
-                animateToWorkspace(mCurrentAnimation, mAnimationDuration);
-            } else {
-                calculateDuration(velocity, Math.abs(mAppsView.getTranslationY()));
-                animateToAllApps(mCurrentAnimation, mAnimationDuration);
-            }
-        }
-        mCurrentAnimation.start();
+        return ((mShiftRange - progress)/ mShiftRange);
     }
 
     private void calculateDuration(float velocity, float disp) {
         // TODO: make these values constants after tuning.
         float velocityDivisor = Math.max(1.5f, Math.abs(0.5f * velocity));
-        float travelDistance = Math.max(0.2f, disp / mTranslation);
+        float travelDistance = Math.max(0.2f, disp / mShiftRange);
         mAnimationDuration = (long) Math.max(100, ANIMATION_DURATION / velocityDivisor * travelDistance);
         if (DBG) {
             Log.d(TAG, String.format("calculateDuration=%d, v=%f, d=%f", mAnimationDuration, velocity, disp));
         }
     }
 
-    public void animateToAllApps(AnimatorSet animationOut, long duration) {
+    public void animateToAllApps(AnimatorSet animationOut, long duration, boolean start) {
         if (animationOut == null){
             return;
         }
         if (mDetector.isRestingState()) {
             preparePull(true);
             mAnimationDuration = duration;
-            mStateAlreadyChanged = true;
+            mShiftStart = mAppsView.getTranslationY();
         }
-        mCurY = mAppsView.getTranslationY();
         final float fromAllAppsTop = mAppsView.getTranslationY();
         final float toAllAppsTop = 0;
 
@@ -311,19 +366,22 @@
                 }
             }});
         mCurrentAnimation = animationOut;
+        if (start) {
+            mCurrentAnimation.start();
+        }
     }
 
-    public void animateToWorkspace(AnimatorSet animationOut, long duration) {
+    public void animateToWorkspace(AnimatorSet animationOut, long duration, boolean start) {
         if (animationOut == null){
             return;
         }
         if(mDetector.isRestingState()) {
             preparePull(true);
             mAnimationDuration = duration;
-            mStateAlreadyChanged = true;
+            mShiftStart = mAppsView.getTranslationY();
         }
         final float fromAllAppsTop = mAppsView.getTranslationY();
-        final float toAllAppsTop = mTranslation;
+        final float toAllAppsTop = mShiftRange;
 
         ObjectAnimator driftAndAlpha = ObjectAnimator.ofFloat(this, "progress",
                 fromAllAppsTop, toAllAppsTop);
@@ -336,6 +394,7 @@
              @Override
              public void onAnimationCancel(Animator animation) {
                  canceled = true;
+                 setProgress(mShiftCurrent);
              }
 
              @Override
@@ -349,16 +408,14 @@
                  }
              }});
         mCurrentAnimation = animationOut;
+        if (start) {
+            mCurrentAnimation.start();
+        }
     }
 
     private void finishPullUp() {
         mHotseat.setVisibility(View.INVISIBLE);
         setProgress(0f);
-        if (!mStateAlreadyChanged) {
-            mLauncher.showAppsView(false /* animated */, true /* resetListToTop */,
-                    false /* updatePredictedApps */, false /* focusSearchBar */);
-        }
-        mStateAlreadyChanged = false;
     }
 
     public void finishPullDown() {
@@ -368,15 +425,12 @@
         mAppsView.setVisibility(View.INVISIBLE);
         mHotseat.setBackgroundTransparent(false /* transparent */);
         mHotseat.setVisibility(View.VISIBLE);
-        setProgress(mTranslation);
-        if (!mStateAlreadyChanged) {
-            mLauncher.showWorkspace(false);
-        }
-        mStateAlreadyChanged = false;
+        setProgress(mShiftRange);
     }
 
     private void cancelAnimation() {
         if (mCurrentAnimation != null) {
+            mCurrentAnimation.setDuration(0);
             mCurrentAnimation.cancel();
             mCurrentAnimation = null;
         }
diff --git a/src/com/android/launcher3/allapps/VerticalPullDetector.java b/src/com/android/launcher3/allapps/VerticalPullDetector.java
index 9304aac..b54cb00 100644
--- a/src/com/android/launcher3/allapps/VerticalPullDetector.java
+++ b/src/com/android/launcher3/allapps/VerticalPullDetector.java
@@ -7,16 +7,22 @@
 
 /**
  * One dimensional scroll gesture detector for all apps container pull up interaction.
+ * Client (e.g., AllAppsTransitionController) of this class can register a listener.
+ *
+ * Features that this gesture detector can support.
  */
 public class VerticalPullDetector {
 
-    private static final String TAG = "ScrollGesture";
     private static final boolean DBG = false;
+    private static final String TAG = "VerticalPullDetector";
 
     private float mTouchSlop;
-    private boolean mScrollDown; // if false, only scroll up will be reported.
-    private boolean mDisallowRecatchFromTop;
-    private boolean mDisallowRecatchFromBottom;
+
+    private int mScrollDirections;
+    public static final int THRESHOLD_UP = 1 << 0;
+    public static final int THRESHOLD_DOWN = 1 << 1;
+    public static final int THRESHOLD_ONLY = THRESHOLD_DOWN | THRESHOLD_UP;
+
 
     /**
      * The minimum release velocity in pixels per millisecond that triggers fling..
@@ -31,23 +37,43 @@
 
     /* Scroll state, this is set to true during dragging and animation. */
     private State mState = State.NONE;
-    enum State {NONE, DRAG, SCROLLING};
+
+    enum State {
+        NONE,
+        CATCH,          // onScrollStart
+        DRAG,           // onScrollStart, onScroll
+        SCROLLING       // onScrollEnd
+    };
+
+    //------------------- State transition diagram -----------------------------------
+    //
+    // NONE -> (mDisplacement > mTouchSlop) -> DRAG
+    // DRAG -> (MotionEvent#ACTION_UP, MotionEvent#ACTION_CANCEL) -> SCROLLING
+    // SCROLLING -> (MotionEvent#ACTION_DOWN) && (mDisplacement > mTouchSlop) -> CATCH
+    // SCROLLING -> (View settled) -> NONE
 
     private void setState(State newState) {
         if (DBG) {
-            Log.d(TAG, mState + "->" + newState);
+            Log.d(TAG, "setState:" + mState + "->" + newState);
         }
         mState = newState;
     }
 
     public boolean shouldIntercept() {
-        return mState == State.DRAG;
+        return mState == State.DRAG || mState == State.SCROLLING || mState == State.CATCH;
     }
 
+    /**
+     * There's no touch and there's no animation.
+     */
     public boolean isRestingState() {
         return mState == State.NONE;
     }
 
+    public boolean isScrollingState() {
+        return mState == State.SCROLLING;
+    }
+
     private float mDownX;
     private float mDownY;
     private float mDownMillis;
@@ -60,8 +86,7 @@
     private float mDisplacementY;
     private float mDisplacementX;
 
-    /* scroll started during previous animation */
-    private boolean mSubtractSlop = true;
+    private float mSubtractDisplacement;
 
     /* Client of this gesture detector can register a callback. */
     Listener mListener;
@@ -80,39 +105,25 @@
         mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();
     }
 
-    public void setDetectableScrollConditions(boolean scrollDown, boolean disallowRecatchFromTop,
-            boolean disallowRecatchFromBottom) {
-        mScrollDown = scrollDown;
-        mDisallowRecatchFromTop = disallowRecatchFromTop;
-        mDisallowRecatchFromBottom = disallowRecatchFromBottom;
+    public void setDetectableScrollConditions(int scrollDirectionFlags) {
+        mScrollDirections = scrollDirectionFlags;
     }
 
     private boolean shouldScrollStart() {
+        // reject cases where the slop condition is not met.
+        if (Math.abs(mDisplacementY) < mTouchSlop) {
+            return false;
+        }
+
+        // reject cases where the angle condition is not met.
         float deltaY = Math.abs(mDisplacementY);
         float deltaX = Math.max(Math.abs(mDisplacementX), 1);
-        if (mScrollDown && mDisplacementY > mTouchSlop) {
-            if (deltaY > deltaX) {
-                return true;
-            }
+        if (deltaX > deltaY) {
+            return false;
         }
-        if (!mScrollDown && mDisplacementY < -mTouchSlop) {
-            if (deltaY > deltaX) {
-                return true;
-            }
-        }
-        return false;
-    }
-
-    private boolean shouldRecatchScrollStart() {
-        if (!mDisallowRecatchFromBottom && !mDisallowRecatchFromTop) {
-            return true;
-        }
-        if (mDisallowRecatchFromTop && mDisplacementY > mTouchSlop) {
-            mDisallowRecatchFromTop = false;
-            return true;
-        }
-        if (mDisallowRecatchFromBottom && mDisplacementY < -mTouchSlop) {
-            mDisallowRecatchFromBottom = false;
+        // Check if the client is interested in scroll in current direction.
+        if (((mScrollDirections & THRESHOLD_DOWN) > 0 && mDisplacementY > 0) ||
+            ((mScrollDirections & THRESHOLD_UP) > 0 && mDisplacementY < 0)) {
             return true;
         }
         return false;
@@ -126,8 +137,11 @@
                 mDownY = ev.getY();
                 mLastDisplacement = 0;
                 mVelocity = 0;
-                if (mState == State.SCROLLING && shouldRecatchScrollStart()){
+
+                // handle state and listener calls.
+                if (mState == State.SCROLLING && shouldScrollStart()){
                     reportScrollStart(true /* recatch */);
+                    setState(State.CATCH);
                 }
                 break;
             case MotionEvent.ACTION_MOVE:
@@ -135,23 +149,23 @@
                 mDisplacementY = ev.getY() - mDownY;
                 mVelocity = computeVelocity(ev, mVelocity);
 
-                if (mState == State.SCROLLING && Math.abs(mDisplacementY) > mTouchSlop ){
+                // handle state and listener calls.
+                if (shouldScrollStart() && mState != State.DRAG) {
+                    if (mState == State.NONE) {
+                        reportScrollStart(false /* recatch */);
+                    }
                     setState(State.DRAG);
-                    reportScrollStart(true /* recatch */);
                 }
-                if (mState == State.NONE && shouldScrollStart()) {
-                    setState(State.DRAG);
-                    reportScrollStart(false /* recatch */);
-                }
-                if (mState == State.DRAG && mListener != null) {
+                if (mState == State.DRAG) {
                     reportScroll();
                 }
                 break;
             case MotionEvent.ACTION_CANCEL:
             case MotionEvent.ACTION_UP:
                 // These are synthetic events and there is no need to update internal values.
-                if (mState == State.DRAG && mListener != null) {
+                if (mState == State.DRAG || mState == State.CATCH) {
                     reportScrollEnd();
+                    setState(State.SCROLLING);
                 }
                 break;
             default:
@@ -173,7 +187,11 @@
 
     private boolean reportScrollStart(boolean recatch) {
         mListener.onScrollStart(!recatch);
-        mSubtractSlop = !recatch;
+        if (mDisplacementY > 0) {
+            mSubtractDisplacement = mTouchSlop;
+        } else {
+            mSubtractDisplacement = -mTouchSlop;
+        }
         if (DBG) {
             Log.d(TAG, "onScrollStart recatch:" + recatch);
         }
@@ -187,15 +205,8 @@
                 Log.d(TAG, String.format("onScroll disp=%.1f, velocity=%.1f",
                         mDisplacementY, mVelocity));
             }
-            float subtractDisplacement = 0f;
-            if (mSubtractSlop) {
-                if (mDisplacementY > 0) {
-                    subtractDisplacement = mTouchSlop;
-                } else {
-                    subtractDisplacement = -mTouchSlop;
-                }
-            }
-            return mListener.onScroll(mDisplacementY - subtractDisplacement, mVelocity);
+
+            return mListener.onScroll(mDisplacementY - mSubtractDisplacement, mVelocity);
         }
         return true;
     }
@@ -206,7 +217,7 @@
                     mDisplacementY, mVelocity));
         }
         mListener.onScrollEnd(mVelocity, Math.abs(mVelocity) > RELEASE_VELOCITY_PX_MS);
-        setState(State.SCROLLING);
+
     }
     /**
      * Computes the damped velocity using the two motion events and the previous velocity.