new3d/src/com/android/gallery3d/anim/Animation.java

package com.android.gallery3d.anim;

import android.view.animation.Interpolator;

import com.android.gallery3d.util.Utils;

// Animation calculates a value according to the current input time.
//
// 1. First we need to use setDuration(int) to set the duration of the
//    animation. The duration is in milliseconds.
// 2. Then we should call start(). The actual start time is the first value
//    passed to calculate(long).
// 3. Each time we want to get an animation value, we call
//    calculate(long currentTimeMillis) to ask the Animation to calculate it.
//    The parameter passed to calculate(long) should be nonnegative.
// 4. Use get() to get that value.
//
// In step 3, onCalculate(float progress) is called so subclasses can calculate
// the value according to progress (progress is a value in [0,1]).
//
// Before onCalculate(float) is called, There is an optional interpolator which
// can change the progress value. The interpolator can be set by
// setInterpolator(Interpolator). If the interpolator is used, the value passed
// to onCalculate may be (for example, the overshoot effect).
//
// The isActive() method returns true after the animation start() is called and
// before calculate is passed a value which reaches the duration of the
// animation.
//
// The start() method can be called again to restart the Animation.
//
abstract public class Animation {
    private static final long ANIMATION_START = -1;
    private static final long NO_ANIMATION = -2;

    private long mStartTime = NO_ANIMATION;
    private int mDuration;
    private Interpolator mInterpolator;

    public void setInterpolator(Interpolator interpolator) {
        mInterpolator = interpolator;
    }

    public void setDuration(int duration) {
        mDuration = duration;
    }

    public void start() {
        mStartTime = ANIMATION_START;
    }

    public void setStartTime(long time) {
        mStartTime = time;
    }

    public boolean isActive() {
        return mStartTime != NO_ANIMATION;
    }

    public boolean calculate(long currentTimeMillis) {
        if (mStartTime == NO_ANIMATION) return false;
        if (mStartTime == ANIMATION_START) mStartTime = currentTimeMillis;
        int elapse = (int) (currentTimeMillis - mStartTime);
        float x = Utils.clamp((float) elapse / mDuration, 0f, 1f);
        onCalculate(mInterpolator != null
                ? mInterpolator.getInterpolation(x)
                : x);
        if (elapse >= mDuration) {
            mStartTime = NO_ANIMATION;
            return false;
        } else {
            return true;
        }
    }

    abstract protected void onCalculate(float progress);
}