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      1 /*
      2  * Copyright 2013 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *     http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.example.android.interactivechart;
     18 
     19 import android.content.Context;
     20 import android.os.SystemClock;
     21 import android.view.animation.DecelerateInterpolator;
     22 import android.view.animation.Interpolator;
     23 
     24 /**
     25  * A simple class that animates double-touch zoom gestures. Functionally similar to a {@link
     26  * android.widget.Scroller}.
     27  */
     28 public class Zoomer {
     29     /**
     30      * The interpolator, used for making zooms animate 'naturally.'
     31      */
     32     private Interpolator mInterpolator;
     33 
     34     /**
     35      * The total animation duration for a zoom.
     36      */
     37     private int mAnimationDurationMillis;
     38 
     39     /**
     40      * Whether or not the current zoom has finished.
     41      */
     42     private boolean mFinished = true;
     43 
     44     /**
     45      * The current zoom value; computed by {@link #computeZoom()}.
     46      */
     47     private float mCurrentZoom;
     48 
     49     /**
     50      * The time the zoom started, computed using {@link android.os.SystemClock#elapsedRealtime()}.
     51      */
     52     private long mStartRTC;
     53 
     54     /**
     55      * The destination zoom factor.
     56      */
     57     private float mEndZoom;
     58 
     59     public Zoomer(Context context) {
     60         mInterpolator = new DecelerateInterpolator();
     61         mAnimationDurationMillis = context.getResources().getInteger(
     62                 android.R.integer.config_shortAnimTime);
     63     }
     64 
     65     /**
     66      * Forces the zoom finished state to the given value. Unlike {@link #abortAnimation()}, the
     67      * current zoom value isn't set to the ending value.
     68      *
     69      * @see android.widget.Scroller#forceFinished(boolean)
     70      */
     71     public void forceFinished(boolean finished) {
     72         mFinished = finished;
     73     }
     74 
     75     /**
     76      * Aborts the animation, setting the current zoom value to the ending value.
     77      *
     78      * @see android.widget.Scroller#abortAnimation()
     79      */
     80     public void abortAnimation() {
     81         mFinished = true;
     82         mCurrentZoom = mEndZoom;
     83     }
     84 
     85     /**
     86      * Starts a zoom from 1.0 to (1.0 + endZoom). That is, to zoom from 100% to 125%, endZoom should
     87      * by 0.25f.
     88      *
     89      * @see android.widget.Scroller#startScroll(int, int, int, int)
     90      */
     91     public void startZoom(float endZoom) {
     92         mStartRTC = SystemClock.elapsedRealtime();
     93         mEndZoom = endZoom;
     94 
     95         mFinished = false;
     96         mCurrentZoom = 1f;
     97     }
     98 
     99     /**
    100      * Computes the current zoom level, returning true if the zoom is still active and false if the
    101      * zoom has finished.
    102      *
    103      * @see android.widget.Scroller#computeScrollOffset()
    104      */
    105     public boolean computeZoom() {
    106         if (mFinished) {
    107             return false;
    108         }
    109 
    110         long tRTC = SystemClock.elapsedRealtime() - mStartRTC;
    111         if (tRTC >= mAnimationDurationMillis) {
    112             mFinished = true;
    113             mCurrentZoom = mEndZoom;
    114             return false;
    115         }
    116 
    117         float t = tRTC * 1f / mAnimationDurationMillis;
    118         mCurrentZoom = mEndZoom * mInterpolator.getInterpolation(t);
    119         return true;
    120     }
    121 
    122     /**
    123      * Returns the current zoom level.
    124      *
    125      * @see android.widget.Scroller#getCurrX()
    126      */
    127     public float getCurrZoom() {
    128         return mCurrentZoom;
    129     }
    130 }
    131