Syncing up state transition with paging transition

Change-Id: Id91e4c046cfe7d9aa6e7de10dbf57ee727ba160e

5 files changed, 611 insertions, 146 deletions

diff --git a/src/com/android/launcher3/LauncherScroller.java b/src/com/android/launcher3/LauncherScroller.java
new file mode 100644
index 000000000..3bd0a78c4
--- /dev/null
+++ b/src/com/android/launcher3/LauncherScroller.java
@@ -0,0 +1,559 @@
+/*
+ * Copyright (C) 2006 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.launcher3;
+
+import android.animation.TimeInterpolator;
+import android.content.Context;
+import android.hardware.SensorManager;
+import android.os.Build;
+import android.util.FloatMath;
+import android.view.ViewConfiguration;
+import android.view.animation.AnimationUtils;
+import android.view.animation.Interpolator;
+
+/**
+ * This class differs from the framework {@link android.widget.Scroller} in that
+ * you can modify the Interpolator post-construction.
+ */
+public class LauncherScroller  {
+    private int mMode;
+
+    private int mStartX;
+    private int mStartY;
+    private int mFinalX;
+    private int mFinalY;
+
+    private int mMinX;
+    private int mMaxX;
+    private int mMinY;
+    private int mMaxY;
+
+    private int mCurrX;
+    private int mCurrY;
+    private long mStartTime;
+    private int mDuration;
+    private float mDurationReciprocal;
+    private float mDeltaX;
+    private float mDeltaY;
+    private boolean mFinished;
+    private TimeInterpolator mInterpolator;
+    private boolean mFlywheel;
+
+    private float mVelocity;
+    private float mCurrVelocity;
+    private int mDistance;
+
+    private float mFlingFriction = ViewConfiguration.getScrollFriction();
+
+    private static final int DEFAULT_DURATION = 250;
+    private static final int SCROLL_MODE = 0;
+    private static final int FLING_MODE = 1;
+
+    private static float DECELERATION_RATE = (float) (Math.log(0.78) / Math.log(0.9));
+    private static final float INFLEXION = 0.35f; // Tension lines cross at (INFLEXION, 1)
+    private static final float START_TENSION = 0.5f;
+    private static final float END_TENSION = 1.0f;
+    private static final float P1 = START_TENSION * INFLEXION;
+    private static final float P2 = 1.0f - END_TENSION * (1.0f - INFLEXION);
+
+    private static final int NB_SAMPLES = 100;
+    private static final float[] SPLINE_POSITION = new float[NB_SAMPLES + 1];
+    private static final float[] SPLINE_TIME = new float[NB_SAMPLES + 1];
+
+    private float mDeceleration;
+    private final float mPpi;
+
+    // A context-specific coefficient adjusted to physical values.
+    private float mPhysicalCoeff;
+
+    static {
+        float x_min = 0.0f;
+        float y_min = 0.0f;
+        for (int i = 0; i < NB_SAMPLES; i++) {
+            final float alpha = (float) i / NB_SAMPLES;
+
+            float x_max = 1.0f;
+            float x, tx, coef;
+            while (true) {
+                x = x_min + (x_max - x_min) / 2.0f;
+                coef = 3.0f * x * (1.0f - x);
+                tx = coef * ((1.0f - x) * P1 + x * P2) + x * x * x;
+                if (Math.abs(tx - alpha) < 1E-5) break;
+                if (tx > alpha) x_max = x;
+                else x_min = x;
+            }
+            SPLINE_POSITION[i] = coef * ((1.0f - x) * START_TENSION + x) + x * x * x;
+
+            float y_max = 1.0f;
+            float y, dy;
+            while (true) {
+                y = y_min + (y_max - y_min) / 2.0f;
+                coef = 3.0f * y * (1.0f - y);
+                dy = coef * ((1.0f - y) * START_TENSION + y) + y * y * y;
+                if (Math.abs(dy - alpha) < 1E-5) break;
+                if (dy > alpha) y_max = y;
+                else y_min = y;
+            }
+            SPLINE_TIME[i] = coef * ((1.0f - y) * P1 + y * P2) + y * y * y;
+        }
+        SPLINE_POSITION[NB_SAMPLES] = SPLINE_TIME[NB_SAMPLES] = 1.0f;
+
+        // This controls the viscous fluid effect (how much of it)
+        sViscousFluidScale = 8.0f;
+        // must be set to 1.0 (used in viscousFluid())
+        sViscousFluidNormalize = 1.0f;
+        sViscousFluidNormalize = 1.0f / viscousFluid(1.0f);
+
+    }
+
+    private static float sViscousFluidScale;
+    private static float sViscousFluidNormalize;
+
+    public void setInterpolator(TimeInterpolator interpolator) {
+        mInterpolator = interpolator;
+    }
+
+    /**
+     * Create a Scroller with the default duration and interpolator.
+     */
+    public LauncherScroller(Context context) {
+        this(context, null);
+    }
+
+    /**
+     * Create a Scroller with the specified interpolator. If the interpolator is
+     * null, the default (viscous) interpolator will be used. "Flywheel" behavior will
+     * be in effect for apps targeting Honeycomb or newer.
+     */
+    public LauncherScroller(Context context, Interpolator interpolator) {
+        this(context, interpolator,
+                context.getApplicationInfo().targetSdkVersion >= Build.VERSION_CODES.HONEYCOMB);
+    }
+
+    /**
+     * Create a Scroller with the specified interpolator. If the interpolator is
+     * null, the default (viscous) interpolator will be used. Specify whether or
+     * not to support progressive "flywheel" behavior in flinging.
+     */
+    public LauncherScroller(Context context, Interpolator interpolator, boolean flywheel) {
+        mFinished = true;
+        mInterpolator = interpolator;
+        mPpi = context.getResources().getDisplayMetrics().density * 160.0f;
+        mDeceleration = computeDeceleration(ViewConfiguration.getScrollFriction());
+        mFlywheel = flywheel;
+
+        mPhysicalCoeff = computeDeceleration(0.84f); // look and feel tuning
+    }
+
+    /**
+     * The amount of friction applied to flings. The default value
+     * is {@link ViewConfiguration#getScrollFriction}.
+     *
+     * @param friction A scalar dimension-less value representing the coefficient of
+     *         friction.
+     */
+    public final void setFriction(float friction) {
+        mDeceleration = computeDeceleration(friction);
+        mFlingFriction = friction;
+    }
+
+    private float computeDeceleration(float friction) {
+        return SensorManager.GRAVITY_EARTH   // g (m/s^2)
+                      * 39.37f               // inch/meter
+                      * mPpi                 // pixels per inch
+                      * friction;
+    }
+
+    /**
+     *
+     * Returns whether the scroller has finished scrolling.
+     *
+     * @return True if the scroller has finished scrolling, false otherwise.
+     */
+    public final boolean isFinished() {
+        return mFinished;
+    }
+
+    /**
+     * Force the finished field to a particular value.
+     *
+     * @param finished The new finished value.
+     */
+    public final void forceFinished(boolean finished) {
+        mFinished = finished;
+    }
+
+    /**
+     * Returns how long the scroll event will take, in milliseconds.
+     *
+     * @return The duration of the scroll in milliseconds.
+     */
+    public final int getDuration() {
+        return mDuration;
+    }
+
+    /**
+     * Returns the current X offset in the scroll.
+     *
+     * @return The new X offset as an absolute distance from the origin.
+     */
+    public final int getCurrX() {
+        return mCurrX;
+    }
+
+    /**
+     * Returns the current Y offset in the scroll.
+     *
+     * @return The new Y offset as an absolute distance from the origin.
+     */
+    public final int getCurrY() {
+        return mCurrY;
+    }
+
+    /**
+     * Returns the current velocity.
+     *
+     * @return The original velocity less the deceleration. Result may be
+     * negative.
+     */
+    public float getCurrVelocity() {
+        return mMode == FLING_MODE ?
+                mCurrVelocity : mVelocity - mDeceleration * timePassed() / 2000.0f;
+    }
+
+    /**
+     * Returns the start X offset in the scroll.
+     *
+     * @return The start X offset as an absolute distance from the origin.
+     */
+    public final int getStartX() {
+        return mStartX;
+    }
+
+    /**
+     * Returns the start Y offset in the scroll.
+     *
+     * @return The start Y offset as an absolute distance from the origin.
+     */
+    public final int getStartY() {
+        return mStartY;
+    }
+
+    /**
+     * Returns where the scroll will end. Valid only for "fling" scrolls.
+     *
+     * @return The final X offset as an absolute distance from the origin.
+     */
+    public final int getFinalX() {
+        return mFinalX;
+    }
+
+    /**
+     * Returns where the scroll will end. Valid only for "fling" scrolls.
+     *
+     * @return The final Y offset as an absolute distance from the origin.
+     */
+    public final int getFinalY() {
+        return mFinalY;
+    }
+
+    /**
+     * Call this when you want to know the new location.  If it returns true,
+     * the animation is not yet finished.
+     */
+    public boolean computeScrollOffset() {
+        if (mFinished) {
+            return false;
+        }
+
+        int timePassed = (int)(AnimationUtils.currentAnimationTimeMillis() - mStartTime);
+
+        if (timePassed < mDuration) {
+            switch (mMode) {
+            case SCROLL_MODE:
+                float x = timePassed * mDurationReciprocal;
+
+                if (mInterpolator == null)
+                    x = viscousFluid(x);
+                else
+                    x = mInterpolator.getInterpolation(x);
+
+                mCurrX = mStartX + Math.round(x * mDeltaX);
+                mCurrY = mStartY + Math.round(x * mDeltaY);
+                break;
+            case FLING_MODE:
+                final float t = (float) timePassed / mDuration;
+                final int index = (int) (NB_SAMPLES * t);
+                float distanceCoef = 1.f;
+                float velocityCoef = 0.f;
+                if (index < NB_SAMPLES) {
+                    final float t_inf = (float) index / NB_SAMPLES;
+                    final float t_sup = (float) (index + 1) / NB_SAMPLES;
+                    final float d_inf = SPLINE_POSITION[index];
+                    final float d_sup = SPLINE_POSITION[index + 1];
+                    velocityCoef = (d_sup - d_inf) / (t_sup - t_inf);
+                    distanceCoef = d_inf + (t - t_inf) * velocityCoef;
+                }
+
+                mCurrVelocity = velocityCoef * mDistance / mDuration * 1000.0f;
+
+                mCurrX = mStartX + Math.round(distanceCoef * (mFinalX - mStartX));
+                // Pin to mMinX <= mCurrX <= mMaxX
+                mCurrX = Math.min(mCurrX, mMaxX);
+                mCurrX = Math.max(mCurrX, mMinX);
+
+                mCurrY = mStartY + Math.round(distanceCoef * (mFinalY - mStartY));
+                // Pin to mMinY <= mCurrY <= mMaxY
+                mCurrY = Math.min(mCurrY, mMaxY);
+                mCurrY = Math.max(mCurrY, mMinY);
+
+                if (mCurrX == mFinalX && mCurrY == mFinalY) {
+                    mFinished = true;
+                }
+
+                break;
+            }
+        }
+        else {
+            mCurrX = mFinalX;
+            mCurrY = mFinalY;
+            mFinished = true;
+        }
+        return true;
+    }
+
+    /**
+     * Start scrolling by providing a starting point and the distance to travel.
+     * The scroll will use the default value of 250 milliseconds for the
+     * duration.
+     *
+     * @param startX Starting horizontal scroll offset in pixels. Positive
+     *        numbers will scroll the content to the left.
+     * @param startY Starting vertical scroll offset in pixels. Positive numbers
+     *        will scroll the content up.
+     * @param dx Horizontal distance to travel. Positive numbers will scroll the
+     *        content to the left.
+     * @param dy Vertical distance to travel. Positive numbers will scroll the
+     *        content up.
+     */
+    public void startScroll(int startX, int startY, int dx, int dy) {
+        startScroll(startX, startY, dx, dy, DEFAULT_DURATION);
+    }
+
+    /**
+     * Start scrolling by providing a starting point, the distance to travel,
+     * and the duration of the scroll.
+     *
+     * @param startX Starting horizontal scroll offset in pixels. Positive
+     *        numbers will scroll the content to the left.
+     * @param startY Starting vertical scroll offset in pixels. Positive numbers
+     *        will scroll the content up.
+     * @param dx Horizontal distance to travel. Positive numbers will scroll the
+     *        content to the left.
+     * @param dy Vertical distance to travel. Positive numbers will scroll the
+     *        content up.
+     * @param duration Duration of the scroll in milliseconds.
+     */
+    public void startScroll(int startX, int startY, int dx, int dy, int duration) {
+        mMode = SCROLL_MODE;
+        mFinished = false;
+        mDuration = duration;
+        mStartTime = AnimationUtils.currentAnimationTimeMillis();
+        mStartX = startX;
+        mStartY = startY;
+        mFinalX = startX + dx;
+        mFinalY = startY + dy;
+        mDeltaX = dx;
+        mDeltaY = dy;
+        mDurationReciprocal = 1.0f / (float) mDuration;
+    }
+
+    /**
+     * Start scrolling based on a fling gesture. The distance travelled will
+     * depend on the initial velocity of the fling.
+     *
+     * @param startX Starting point of the scroll (X)
+     * @param startY Starting point of the scroll (Y)
+     * @param velocityX Initial velocity of the fling (X) measured in pixels per
+     *        second.
+     * @param velocityY Initial velocity of the fling (Y) measured in pixels per
+     *        second
+     * @param minX Minimum X value. The scroller will not scroll past this
+     *        point.
+     * @param maxX Maximum X value. The scroller will not scroll past this
+     *        point.
+     * @param minY Minimum Y value. The scroller will not scroll past this
+     *        point.
+     * @param maxY Maximum Y value. The scroller will not scroll past this
+     *        point.
+     */
+    public void fling(int startX, int startY, int velocityX, int velocityY,
+            int minX, int maxX, int minY, int maxY) {
+        // Continue a scroll or fling in progress
+        if (mFlywheel && !mFinished) {
+            float oldVel = getCurrVelocity();
+
+            float dx = (float) (mFinalX - mStartX);
+            float dy = (float) (mFinalY - mStartY);
+            float hyp = FloatMath.sqrt(dx * dx + dy * dy);
+
+            float ndx = dx / hyp;
+            float ndy = dy / hyp;
+
+            float oldVelocityX = ndx * oldVel;
+            float oldVelocityY = ndy * oldVel;
+            if (Math.signum(velocityX) == Math.signum(oldVelocityX) &&
+                    Math.signum(velocityY) == Math.signum(oldVelocityY)) {
+                velocityX += oldVelocityX;
+                velocityY += oldVelocityY;
+            }
+        }
+
+        mMode = FLING_MODE;
+        mFinished = false;
+
+        float velocity = FloatMath.sqrt(velocityX * velocityX + velocityY * velocityY);
+
+        mVelocity = velocity;
+        mDuration = getSplineFlingDuration(velocity);
+        mStartTime = AnimationUtils.currentAnimationTimeMillis();
+        mStartX = startX;
+        mStartY = startY;
+
+        float coeffX = velocity == 0 ? 1.0f : velocityX / velocity;
+        float coeffY = velocity == 0 ? 1.0f : velocityY / velocity;
+
+        double totalDistance = getSplineFlingDistance(velocity);
+        mDistance = (int) (totalDistance * Math.signum(velocity));
+
+        mMinX = minX;
+        mMaxX = maxX;
+        mMinY = minY;
+        mMaxY = maxY;
+
+        mFinalX = startX + (int) Math.round(totalDistance * coeffX);
+        // Pin to mMinX <= mFinalX <= mMaxX
+        mFinalX = Math.min(mFinalX, mMaxX);
+        mFinalX = Math.max(mFinalX, mMinX);
+
+        mFinalY = startY + (int) Math.round(totalDistance * coeffY);
+        // Pin to mMinY <= mFinalY <= mMaxY
+        mFinalY = Math.min(mFinalY, mMaxY);
+        mFinalY = Math.max(mFinalY, mMinY);
+    }
+
+    private double getSplineDeceleration(float velocity) {
+        return Math.log(INFLEXION * Math.abs(velocity) / (mFlingFriction * mPhysicalCoeff));
+    }
+
+    private int getSplineFlingDuration(float velocity) {
+        final double l = getSplineDeceleration(velocity);
+        final double decelMinusOne = DECELERATION_RATE - 1.0;
+        return (int) (1000.0 * Math.exp(l / decelMinusOne));
+    }
+
+    private double getSplineFlingDistance(float velocity) {
+        final double l = getSplineDeceleration(velocity);
+        final double decelMinusOne = DECELERATION_RATE - 1.0;
+        return mFlingFriction * mPhysicalCoeff * Math.exp(DECELERATION_RATE / decelMinusOne * l);
+    }
+
+    static float viscousFluid(float x)
+    {
+        x *= sViscousFluidScale;
+        if (x < 1.0f) {
+            x -= (1.0f - (float)Math.exp(-x));
+        } else {
+            float start = 0.36787944117f;   // 1/e == exp(-1)
+            x = 1.0f - (float)Math.exp(1.0f - x);
+            x = start + x * (1.0f - start);
+        }
+        x *= sViscousFluidNormalize;
+        return x;
+    }
+
+    /**
+     * Stops the animation. Contrary to {@link #forceFinished(boolean)},
+     * aborting the animating cause the scroller to move to the final x and y
+     * position
+     *
+     * @see #forceFinished(boolean)
+     */
+    public void abortAnimation() {
+        mCurrX = mFinalX;
+        mCurrY = mFinalY;
+        mFinished = true;
+    }
+
+    /**
+     * Extend the scroll animation. This allows a running animation to scroll
+     * further and longer, when used with {@link #setFinalX(int)} or {@link #setFinalY(int)}.
+     *
+     * @param extend Additional time to scroll in milliseconds.
+     * @see #setFinalX(int)
+     * @see #setFinalY(int)
+     */
+    public void extendDuration(int extend) {
+        int passed = timePassed();
+        mDuration = passed + extend;
+        mDurationReciprocal = 1.0f / mDuration;
+        mFinished = false;
+    }
+
+    /**
+     * Returns the time elapsed since the beginning of the scrolling.
+     *
+     * @return The elapsed time in milliseconds.
+     */
+    public int timePassed() {
+        return (int)(AnimationUtils.currentAnimationTimeMillis() - mStartTime);
+    }
+
+    /**
+     * Sets the final position (X) for this scroller.
+     *
+     * @param newX The new X offset as an absolute distance from the origin.
+     * @see #extendDuration(int)
+     * @see #setFinalY(int)
+     */
+    public void setFinalX(int newX) {
+        mFinalX = newX;
+        mDeltaX = mFinalX - mStartX;
+        mFinished = false;
+    }
+
+    /**
+     * Sets the final position (Y) for this scroller.
+     *
+     * @param newY The new Y offset as an absolute distance from the origin.
+     * @see #extendDuration(int)
+     * @see #setFinalX(int)
+     */
+    public void setFinalY(int newY) {
+        mFinalY = newY;
+        mDeltaY = mFinalY - mStartY;
+        mFinished = false;
+    }
+
+    /**
+     * @hide
+     */
+    public boolean isScrollingInDirection(float xvel, float yvel) {
+        return !mFinished && Math.signum(xvel) == Math.signum(mFinalX - mStartX) &&
+                Math.signum(yvel) == Math.signum(mFinalY - mStartY);
+    }
+}
diff --git a/src/com/android/launcher3/PagedView.java b/src/com/android/launcher3/PagedView.java
index 76d54fc08..b11302c9a 100644
--- a/src/com/android/launcher3/PagedView.java
+++ b/src/com/android/launcher3/PagedView.java
@@ -120,7 +120,8 @@ public abstract class PagedView extends ViewGroup implements ViewGroup.OnHierarc
 
     protected int mNextPage = INVALID_PAGE;
     protected int mMaxScrollX;
-    protected Scroller mScroller;
+    protected LauncherScroller mScroller;
+    private Interpolator mDefaultInterpolator;
     private VelocityTracker mVelocityTracker;
     private int mPageSpacing = 0;
 
@@ -319,7 +320,8 @@ public abstract class PagedView extends ViewGroup implements ViewGroup.OnHierarc
     protected void init() {
         mDirtyPageContent = new ArrayList<Boolean>();
         mDirtyPageContent.ensureCapacity(32);
-        mScroller = new Scroller(getContext(), new ScrollInterpolator());
+        mScroller = new LauncherScroller(getContext());
+        setDefaultInterpolator(new ScrollInterpolator());
         mCurrentPage = 0;
         mCenterPagesVertically = true;
 
@@ -339,6 +341,11 @@ public abstract class PagedView extends ViewGroup implements ViewGroup.OnHierarc
         setOnHierarchyChangeListener(this);
     }
 
+    protected void setDefaultInterpolator(Interpolator interpolator) {
+        mDefaultInterpolator = interpolator;
+        mScroller.setInterpolator(mDefaultInterpolator);
+    }
+
     protected void onAttachedToWindow() {
         super.onAttachedToWindow();
 
@@ -1728,8 +1735,12 @@ public abstract class PagedView extends ViewGroup implements ViewGroup.OnHierarc
         return OVERSCROLL_DAMP_FACTOR * f;
     }
 
-    protected void disableFreeScroll(int snapPage) {
-        setEnableFreeScroll(false, snapPage);
+    protected void enableFreeScroll() {
+        setEnableFreeScroll(true);
+    }
+
+    protected void disableFreeScroll() {
+        setEnableFreeScroll(false);
     }
 
     void updateFreescrollBounds() {
@@ -1743,16 +1754,10 @@ public abstract class PagedView extends ViewGroup implements ViewGroup.OnHierarc
         }
     }
 
-    private void setEnableFreeScroll(boolean freeScroll, int snapPage) {
+    private void setEnableFreeScroll(boolean freeScroll) {
         mFreeScroll = freeScroll;
 
-        if (snapPage == -1) {
-            snapPage = getPageNearestToCenterOfScreen();
-        }
-
-        if (!mFreeScroll) {
-            snapToPage(snapPage);
-        } else {
+        if (mFreeScroll) {
             updateFreescrollBounds();
             getOverviewModePages(mTempVisiblePagesRange);
             if (getCurrentPage() < mTempVisiblePagesRange[0]) {
@@ -2010,6 +2015,7 @@ public abstract class PagedView extends ViewGroup implements ViewGroup.OnHierarc
                     int vX = (int) (-velocityX * scaleX);
                     int initialScrollX = (int) (getScrollX() * scaleX);
 
+                    mScroller.setInterpolator(mDefaultInterpolator);
                     mScroller.fling(initialScrollX,
                             getScrollY(), vX, 0, Integer.MIN_VALUE, Integer.MAX_VALUE, 0, 0);
                     invalidate();
@@ -2284,27 +2290,33 @@ public abstract class PagedView extends ViewGroup implements ViewGroup.OnHierarc
     }
 
     protected void snapToPageImmediately(int whichPage) {
-        snapToPage(whichPage, PAGE_SNAP_ANIMATION_DURATION, true);
+        snapToPage(whichPage, PAGE_SNAP_ANIMATION_DURATION, true, null);
     }
 
     protected void snapToPage(int whichPage, int duration) {
-        snapToPage(whichPage, duration, false);
+        snapToPage(whichPage, duration, false, null);
+    }
+
+    protected void snapToPage(int whichPage, int duration, TimeInterpolator interpolator) {
+        snapToPage(whichPage, duration, false, interpolator);
     }
 
-    protected void snapToPage(int whichPage, int duration, boolean immediate) {
+    protected void snapToPage(int whichPage, int duration, boolean immediate,
+            TimeInterpolator interpolator) {
         whichPage = Math.max(0, Math.min(whichPage, getPageCount() - 1));
 
         int newX = getScrollForPage(whichPage);
         final int sX = mUnboundedScrollX;
         final int delta = newX - sX;
-        snapToPage(whichPage, delta, duration, immediate);
+        snapToPage(whichPage, delta, duration, immediate, interpolator);
     }
 
     protected void snapToPage(int whichPage, int delta, int duration) {
-        snapToPage(whichPage, delta, duration, false);
+        snapToPage(whichPage, delta, duration, false, null);
     }
 
-    protected void snapToPage(int whichPage, int delta, int duration, boolean immediate) {
+    protected void snapToPage(int whichPage, int delta, int duration, boolean immediate,
+            TimeInterpolator interpolator) {
         mNextPage = whichPage;
         View focusedChild = getFocusedChild();
         if (focusedChild != null && whichPage != mCurrentPage &&
@@ -2323,8 +2335,15 @@ public abstract class PagedView extends ViewGroup implements ViewGroup.OnHierarc
         }
 
         if (!mScroller.isFinished()) {
-            mScroller.abortAnimation();
+            abortScrollerAnimation(false);
         }
+
+        if (interpolator != null) {
+            mScroller.setInterpolator(interpolator);
+        } else {
+            mScroller.setInterpolator(mDefaultInterpolator);
+        }
+
         mScroller.startScroll(mUnboundedScrollX, 0, delta, 0, duration);
 
         notifyPageSwitchListener();
@@ -2581,7 +2600,8 @@ public abstract class PagedView extends ViewGroup implements ViewGroup.OnHierarc
             mDragView = getChildAt(dragViewIndex);
             mDragView.animate().scaleX(1.15f).scaleY(1.15f).setDuration(100).start();
             mDragViewBaselineLeft = mDragView.getLeft();
-            disableFreeScroll(-1);
+            snapToPage(getPageNearestToCenterOfScreen());
+            disableFreeScroll();
             onStartReordering();
             return true;
         }
diff --git a/src/com/android/launcher3/RampUpScroller.java b/src/com/android/launcher3/RampUpScroller.java
deleted file mode 100644
index 89eb5798e..000000000
--- a/src/com/android/launcher3/RampUpScroller.java
+++ /dev/null
@@ -1,120 +0,0 @@
-/*
- * Copyright (C) 2013 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.launcher3;
-
-import android.view.animation.AccelerateInterpolator;
-import android.view.animation.AnimationUtils;
-import android.view.animation.Interpolator;
-
-/**
- * Scroller that gradually reaches a target velocity.
- */
-class RampUpScroller {
-    private final Interpolator mInterpolator;
-    private final long mRampUpTime;
-
-    private long mStartTime;
-    private long mDeltaTime;
-    private float mTargetVelocityX;
-    private float mTargetVelocityY;
-    private int mDeltaX;
-    private int mDeltaY;
-
-    /**
-     * Creates a new ramp-up scroller that reaches full velocity after a
-     * specified duration.
-     *
-     * @param rampUpTime Duration before the scroller reaches target velocity.
-     */
-    public RampUpScroller(long rampUpTime) {
-        mInterpolator = new AccelerateInterpolator();
-        mRampUpTime = rampUpTime;
-    }
-
-    /**
-     * Starts the scroller at the current animation time.
-     */
-    public void start() {
-        mStartTime = AnimationUtils.currentAnimationTimeMillis();
-        mDeltaTime = mStartTime;
-    }
-
-    /**
-     * Computes the current scroll deltas. This usually only be called after
-     * starting the scroller with {@link #start()}.
-     *
-     * @see #getDeltaX()
-     * @see #getDeltaY()
-     */
-    public void computeScrollDelta() {
-        final long currentTime = AnimationUtils.currentAnimationTimeMillis();
-        final long elapsedSinceStart = currentTime - mStartTime;
-        final float scale;
-        if (elapsedSinceStart < mRampUpTime) {
-            scale = mInterpolator.getInterpolation((float) elapsedSinceStart / mRampUpTime);
-        } else {
-            scale = 1f;
-        }
-
-        final long elapsedSinceDelta = currentTime - mDeltaTime;
-        mDeltaTime = currentTime;
-
-        mDeltaX = (int) (elapsedSinceDelta * scale * mTargetVelocityX);
-        mDeltaY = (int) (elapsedSinceDelta * scale * mTargetVelocityY);
-    }
-
-    /**
-     * Sets the target velocity for this scroller.
-     *
-     * @param x The target X velocity in pixels per millisecond.
-     * @param y The target Y velocity in pixels per millisecond.
-     */
-    public void setTargetVelocity(float x, float y) {
-        mTargetVelocityX = x;
-        mTargetVelocityY = y;
-    }
-
-    /**
-     * @return The target X velocity for this scroller.
-     */
-    public float getTargetVelocityX() {
-        return mTargetVelocityX;
-    }
-
-    /**
-     * @return The target Y velocity for this scroller.
-     */
-    public float getTargetVelocityY() {
-        return mTargetVelocityY;
-    }
-
-    /**
-     * The distance traveled in the X-coordinate computed by the last call to
-     * {@link #computeScrollDelta()}.
-     */
-    public int getDeltaX() {
-        return mDeltaX;
-    }
-
-    /**
-     * The distance traveled in the Y-coordinate computed by the last call to
-     * {@link #computeScrollDelta()}.
-     */
-    public int getDeltaY() {
-        return mDeltaY;
-    }
-}
diff --git a/src/com/android/launcher3/SmoothPagedView.java b/src/com/android/launcher3/SmoothPagedView.java
index 64dcb34ca..4e331aa2c 100644
--- a/src/com/android/launcher3/SmoothPagedView.java
+++ b/src/com/android/launcher3/SmoothPagedView.java
@@ -19,7 +19,6 @@ package com.android.launcher3;
 import android.content.Context;
 import android.util.AttributeSet;
 import android.view.animation.Interpolator;
-import android.widget.Scroller;
 
 public abstract class SmoothPagedView extends PagedView {
     private static final float SMOOTHING_SPEED = 0.75f;
@@ -100,7 +99,7 @@ public abstract class SmoothPagedView extends PagedView {
             mBaseLineFlingVelocity = 2500.0f;
             mFlingVelocityInfluence = 0.4f;
             mScrollInterpolator = new OvershootInterpolator();
-            mScroller = new Scroller(getContext(), mScrollInterpolator);
+            setDefaultInterpolator(mScrollInterpolator);
         }
     }
 
diff --git a/src/com/android/launcher3/Workspace.java b/src/com/android/launcher3/Workspace.java
index eeb49f8e0..7ba6adf2a 100644
--- a/src/com/android/launcher3/Workspace.java
+++ b/src/com/android/launcher3/Workspace.java
@@ -2234,9 +2234,12 @@ public class Workspace extends SmoothPagedView
         mNewScale = 1.0f;
 
         if (oldStateIsOverview) {
-            disableFreeScroll(snapPage);
+            disableFreeScroll();
+        } else if (stateIsOverview) {
+            enableFreeScroll();
         }
 
+
         if (state != State.NORMAL) {
             if (stateIsSpringLoaded) {
                 mNewScale = mSpringLoadedShrinkFactor;
@@ -2259,16 +2262,20 @@ public class Workspace extends SmoothPagedView
             duration = getResources().getInteger(R.integer.config_appsCustomizeWorkspaceShrinkTime);
         }
 
+        if (snapPage == -1) {
+            snapPage = getPageNearestToCenterOfScreen();
+        }
+        snapToPage(snapPage, duration, mZoomInInterpolator);
+
         for (int i = 0; i < getChildCount(); i++) {
             final CellLayout cl = (CellLayout) getChildAt(i);
-            boolean isCurrentPage = (i == getNextPage());
+            boolean isCurrentPage = (i == snapPage);
             float initialAlpha = cl.getShortcutsAndWidgets().getAlpha();
             float finalAlpha;
             if (stateIsSmall) {
                 finalAlpha = 0f;
             } else if (stateIsNormal && mWorkspaceFadeInAdjacentScreens) {
-
-                finalAlpha = (i == getNextPage() || i < numCustomPages()) ? 1f : 0f;
+                finalAlpha = (i == snapPage || i < numCustomPages()) ? 1f : 0f;
             } else {
                 finalAlpha = 1f;
             }