Syncing up state transition with paging transition

Change-Id: Id91e4c046cfe7d9aa6e7de10dbf57ee727ba160e
diff --git a/src/com/android/launcher3/LauncherScroller.java b/src/com/android/launcher3/LauncherScroller.java
new file mode 100644
index 0000000..3bd0a78
--- /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);
+    }
+}