content: /*
   * 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.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 = (float) Math.hypot(dx, 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 = (float) Math.hypot(velocityX, 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);
      }
  }
  