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      1 /*
      2  * Copyright (C) 2010 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.android.gallery3d.anim;
     18 
     19 import com.android.gallery3d.common.Utils;
     20 
     21 import android.view.animation.Interpolator;
     22 
     23 // Animation calculates a value according to the current input time.
     24 //
     25 // 1. First we need to use setDuration(int) to set the duration of the
     26 //    animation. The duration is in milliseconds.
     27 // 2. Then we should call start(). The actual start time is the first value
     28 //    passed to calculate(long).
     29 // 3. Each time we want to get an animation value, we call
     30 //    calculate(long currentTimeMillis) to ask the Animation to calculate it.
     31 //    The parameter passed to calculate(long) should be nonnegative.
     32 // 4. Use get() to get that value.
     33 //
     34 // In step 3, onCalculate(float progress) is called so subclasses can calculate
     35 // the value according to progress (progress is a value in [0,1]).
     36 //
     37 // Before onCalculate(float) is called, There is an optional interpolator which
     38 // can change the progress value. The interpolator can be set by
     39 // setInterpolator(Interpolator). If the interpolator is used, the value passed
     40 // to onCalculate may be (for example, the overshoot effect).
     41 //
     42 // The isActive() method returns true after the animation start() is called and
     43 // before calculate is passed a value which reaches the duration of the
     44 // animation.
     45 //
     46 // The start() method can be called again to restart the Animation.
     47 //
     48 abstract public class Animation {
     49     private static final long ANIMATION_START = -1;
     50     private static final long NO_ANIMATION = -2;
     51 
     52     private long mStartTime = NO_ANIMATION;
     53     private int mDuration;
     54     private Interpolator mInterpolator;
     55 
     56     public void setInterpolator(Interpolator interpolator) {
     57         mInterpolator = interpolator;
     58     }
     59 
     60     public void setDuration(int duration) {
     61         mDuration = duration;
     62     }
     63 
     64     public void start() {
     65         mStartTime = ANIMATION_START;
     66     }
     67 
     68     public void setStartTime(long time) {
     69         mStartTime = time;
     70     }
     71 
     72     public boolean isActive() {
     73         return mStartTime != NO_ANIMATION;
     74     }
     75 
     76     public void forceStop() {
     77         mStartTime = NO_ANIMATION;
     78     }
     79 
     80     public boolean calculate(long currentTimeMillis) {
     81         if (mStartTime == NO_ANIMATION) return false;
     82         if (mStartTime == ANIMATION_START) mStartTime = currentTimeMillis;
     83         int elapse = (int) (currentTimeMillis - mStartTime);
     84         float x = Utils.clamp((float) elapse / mDuration, 0f, 1f);
     85         Interpolator i = mInterpolator;
     86         onCalculate(i != null ? i.getInterpolation(x) : x);
     87         if (elapse >= mDuration) mStartTime = NO_ANIMATION;
     88         return mStartTime != NO_ANIMATION;
     89     }
     90 
     91     abstract protected void onCalculate(float progress);
     92 }
     93