Android 动画animation 深入分析

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Android 动画animation 深入分析

前言：本文试图通过分析动画流程，来理解android动画系统的设计与实现，学习动画的基本原则，最终希望能够指导动画的设计。

0 本文中用到的一些类图

1 view animation 

调用方法：view.startAnimation(animation);

public void startAnimation(Animation animation) {
    animation.setStartTime(Animation.START_ON_FIRST_FRAME);
    setAnimation(animation);
    invalidateParentCaches();
    invalidate(true);
}

在invalidate(ture);中

if (p != null && ai != null) {
    final Rect r = ai.mTmpInvalRect;
    r.set(0, 0, mRight - mLeft, mBottom - mTop);
    // Don't call invalidate -- we don't want to internally scroll
    // our own bounds
    p.invalidateChild(this, r);
}

即调用parent的invalidateChild，

假定父控件即为ViewRootImpl;

public final class ViewRootImpl implements ViewParent;

@Override
public void invalidateChild(View child, Rect dirty) {
    invalidateChildInParent(null, dirty);
}

public ViewParent invalidateChildInParent(int[] location, Rect dirty) {
    //...省略一堆判断条件，最终调用
    if (!mWillDrawSoon && (intersected || mIsAnimating)) {
        scheduleTraversals();
    }

    return null;
}

void scheduleTraversals() {
    if (!mTraversalScheduled) {
        mTraversalScheduled = true;
        mTraversalBarrier = mHandler.getLooper().postSyncBarrier();
        mChoreographer.postCallback(
                Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
        scheduleConsumeBatchedInput();
    }
}

其中mTraversalBarrier = mHandler.getLooper().postSyncBarrier();是设置同步障碍（syncBarrier），当looper中的消息队列执行到barrier 后，会暂停执行，只有当barrier 被释放mHandler.getLooper().removeSyncBarrier(mTraversalBarrier); 后消息队列才能继续执行。

    Choreographer mChoreographer; 是动画系统中的核心组织者， 负责统一调度。后面详细说。

final TraversalRunnable mTraversalRunnable = new TraversalRunnable();
final class TraversalRunnable implements Runnable {
    @Override
    public void run() {
        doTraversal();
    }
}

    void doTraversal() {
        performTraversals();
    }

perform 待补充

final class ConsumeBatchedInputRunnable implements Runnable {
    @Override
    public void run() {
        doConsumeBatchedInput(mChoreographer.getFrameTimeNanos());
    }
}
final ConsumeBatchedInputRunnable mConsumedBatchedInputRunnable =
        new ConsumeBatchedInputRunnable();

doConsume 待补充

2 属性动画aninmator

valueAnimator.start();

    private void start(boolean playBackwards) {
        if (Looper.myLooper() == null) {
            throw new AndroidRuntimeException("Animators may only be run on Looper threads");
        }
        AnimationHandler animationHandler = getOrCreateAnimationHandler();
        animationHandler.mPendingAnimations.add(this);
        if (mStartDelay == 0) {
            // This sets the initial value of the animation, prior to actually starting it running
            setCurrentPlayTime(0);
            mPlayingState = STOPPED;
            mRunning = true;
            notifyStartListeners();
        }
        animationHandler.start();
    }

这里会检查调用线程必须是Looper线程，如果是view相关的属性动画，还必须是UI 线程。

得到AnimationHandle 并把自己加入到PendingAnimations  的list中.

getOrCreateAnimationHandler();

protected static ThreadLocal<AnimationHandler> sAnimationHandler =
        new ThreadLocal<AnimationHandler>()
protected static class AnimationHandler implements Runnable {
    // The per-thread list of all active animations
    /** @hide */
    protected final ArrayList<ValueAnimator> mAnimations = new ArrayList<ValueAnimator>();

    // Used in doAnimationFrame() to avoid concurrent modifications of mAnimations
    private final ArrayList<ValueAnimator> mTmpAnimations = new ArrayList<ValueAnimator>();

    // The per-thread set of animations to be started on the next animation frame
    /** @hide */
    protected final ArrayList<ValueAnimator> mPendingAnimations = new ArrayList<ValueAnimator>();

    /**
     * Internal per-thread collections used to avoid set collisions as animations start and end
     * while being processed.
     * @hide
     */
    protected final ArrayList<ValueAnimator> mDelayedAnims = new ArrayList<ValueAnimator>();
    private final ArrayList<ValueAnimator> mEndingAnims = new ArrayList<ValueAnimator>();
    private final ArrayList<ValueAnimator> mReadyAnims = new ArrayList<ValueAnimator>();

    private final Choreographer mChoreographer;
    private boolean mAnimationScheduled;

AnimationHandler 就是一个runnable， 注意成员变量中的多个animator 的list 以及重要的mChoreographer = Choreographer.getInstance();

mChoreographer 也是一个threadlocal的变量。

在animationHandler.start() 中

        public void start() {
            scheduleAnimation();
        }
        private void scheduleAnimation() {
            if (!mAnimationScheduled) {
                mChoreographer.postCallback(Choreographer.CALLBACK_ANIMATION, this, null);
                mAnimationScheduled = true;
            }
        }

this 是runnable 即把animationHandler自己添加添加到mChoreographer 的队列中。

    public void postCallback(int callbackType, Runnable action, Object token) {
        postCallbackDelayed(callbackType, action, token, 0);
    }
    public void postCallbackDelayed(int callbackType,
            Runnable action, Object token, long delayMillis) {
        postCallbackDelayedInternal(callbackType, action, token, delayMillis);
    }
    private void postCallbackDelayedInternal(int callbackType,
            Object action, Object token, long delayMillis) {
        synchronized (mLock) {
            final long now = SystemClock.uptimeMillis();
            final long dueTime = now + delayMillis;
            mCallbackQueues[callbackType].addCallbackLocked(dueTime, action, token);

            if (dueTime <= now) {
                scheduleFrameLocked(now);
            } else {
                Message msg = mHandler.obtainMessage(MSG_DO_SCHEDULE_CALLBACK, action);
                msg.arg1 = callbackType;
                msg.setAsynchronous(true);
                mHandler.sendMessageAtTime(msg, dueTime);
            }
        }
    }

传入的delay为0， 即调用scheduleFrameLocked(now);

private void scheduleFrameLocked(long now) {
    if (!mFrameScheduled) {
        mFrameScheduled = true;
        if (USE_VSYNC) {
            if (DEBUG) {
                Log.d(TAG, "Scheduling next frame on vsync.");
            }

            // If running on the Looper thread, then schedule the vsync immediately,
            // otherwise post a message to schedule the vsync from the UI thread
            // as soon as possible.
            if (isRunningOnLooperThreadLocked()) {
                scheduleVsyncLocked();
            } else {
                Message msg = mHandler.obtainMessage(MSG_DO_SCHEDULE_VSYNC);
                msg.setAsynchronous(true);
                mHandler.sendMessageAtFrontOfQueue(msg);
            }
        } else {
            final long nextFrameTime = Math.max(
                    mLastFrameTimeNanos / NANOS_PER_MS + sFrameDelay, now);
            if (DEBUG) {
                Log.d(TAG, "Scheduling next frame in " + (nextFrameTime - now) + " ms.");
            }
            Message msg = mHandler.obtainMessage(MSG_DO_FRAME);
            msg.setAsynchronous(true);
            mHandler.sendMessageAtTime(msg, nextFrameTime);
        }
    }
}

private static final boolean USE_VSYNC = SystemProperties.getBoolean(
        "debug.choreographer.vsync", true);

USE_VSYNC 默认是true；    

private boolean isRunningOnLooperThreadLocked() {
    return Looper.myLooper() == mLooper;
}

检查当前looper和mChoreographer的looper是否一致。一般情况是一致的。就会调用scheduleVsyncLocked();

private void scheduleVsyncLocked() {
    mDisplayEventReceiver.scheduleVsync();
}

public void scheduleVsync() {
    if (mReceiverPtr == 0) {
        Log.w(TAG, "Attempted to schedule a vertical sync pulse but the display event "
                + "receiver has already been disposed.");
    } else {
        nativeScheduleVsync(mReceiverPtr);
    }
}

到了native 暂时先不涉及。

回头来看animationHandler 的run()。 前面提到animationHandler把自己添加到mChoreographer，当被调用时，调用run方法。

// Called by the Choreographer.
@Override
public void run() {
    mAnimationScheduled = false;
    doAnimationFrame(mChoreographer.getFrameTime());
}

    public long getFrameTime() {
        return getFrameTimeNanos() / NANOS_PER_MS;
    }
    public long getFrameTimeNanos() {
        synchronized (mLock) {
            if (!mCallbacksRunning) {
                throw new IllegalStateException("This method must only be called as "
                        + "part of a callback while a frame is in progress.");
            }
            return USE_FRAME_TIME ? mLastFrameTimeNanos : System.nanoTime();
        }
    }

doAnimationFrame()总结就是

1.遍历pending list动画，如果delay为0 则调用start，不为0，加入delay list；

2.遍历delay list， 根据frametime计算是继续delay还是ready可以播放，若是ready，则加入到ready list中；

3 遍历ready list，调用start ；

4，遍历所有animation，根据frametime计算动画是否要结束，如果可以结束，则加入到ending list中；

5，遍历ending list， 调用end；

6， 如果有列表中仍然有动画，则继续scheduleAnimation；

private void doAnimationFrame(long frameTime) {
    // mPendingAnimations holds any animations that have requested to be started
    // We're going to clear mPendingAnimations, but starting animation may
    // cause more to be added to the pending list (for example, if one animation
    // starting triggers another starting). So we loop until mPendingAnimations
    // is empty.
    while (mPendingAnimations.size() > 0) {
        ArrayList<ValueAnimator> pendingCopy =
                (ArrayList<ValueAnimator>) mPendingAnimations.clone();
        mPendingAnimations.clear();
        int count = pendingCopy.size();
        for (int i = 0; i < count; ++i) {
            ValueAnimator anim = pendingCopy.get(i);
            // If the animation has a startDelay, place it on the delayed list
            if (anim.mStartDelay == 0) {
                anim.startAnimation(this);
            } else {
                mDelayedAnims.add(anim);
            }
        }
    }
    // Next, process animations currently sitting on the delayed queue, adding
    // them to the active animations if they are ready
    int numDelayedAnims = mDelayedAnims.size();
    for (int i = 0; i < numDelayedAnims; ++i) {
        ValueAnimator anim = mDelayedAnims.get(i);
        if (anim.delayedAnimationFrame(frameTime)) {
            mReadyAnims.add(anim);
        }
    }
    int numReadyAnims = mReadyAnims.size();
    if (numReadyAnims > 0) {
        for (int i = 0; i < numReadyAnims; ++i) {
            ValueAnimator anim = mReadyAnims.get(i);
            anim.startAnimation(this);
            anim.mRunning = true;
            mDelayedAnims.remove(anim);
        }
        mReadyAnims.clear();
    }

    // Now process all active animations. The return value from animationFrame()
    // tells the handler whether it should now be ended
    int numAnims = mAnimations.size();
    for (int i = 0; i < numAnims; ++i) {
        mTmpAnimations.add(mAnimations.get(i));
    }
    for (int i = 0; i < numAnims; ++i) {
        ValueAnimator anim = mTmpAnimations.get(i);
        if (mAnimations.contains(anim) && anim.doAnimationFrame(frameTime)) {
            mEndingAnims.add(anim);
        }
    }
    mTmpAnimations.clear();
    if (mEndingAnims.size() > 0) {
        for (int i = 0; i < mEndingAnims.size(); ++i) {
            mEndingAnims.get(i).endAnimation(this);
        }
        mEndingAnims.clear();
    }

    // If there are still active or delayed animations, schedule a future call to
    // onAnimate to process the next frame of the animations.
    if (!mAnimations.isEmpty() || !mDelayedAnims.isEmpty()) {
        scheduleAnimation();
    }
}

在animationFrame() 中根据当前状态，并且计算fraction，调用animateValue();

    boolean animationFrame(long currentTime) {
        boolean done = false;
        switch (mPlayingState) {
        case RUNNING:
        case SEEKED:
            //省略计算fraction的代码
            animateValue(fraction);
            break;
        }
        return done;
    }

通过mInterpolator.getInterpolation计算fraction；@Interpolator 

根据fraction计算内部所有value，如果有updateListener，调用之。

void animateValue(float fraction) {
    fraction = mInterpolator.getInterpolation(fraction);
    mCurrentFraction = fraction;
    int numValues = mValues.length;
    for (int i = 0; i < numValues; ++i) {
        mValues[i].calculateValue(fraction);
    }
    if (mUpdateListeners != null) {
        int numListeners = mUpdateListeners.size();
        for (int i = 0; i < numListeners; ++i) {
            mUpdateListeners.get(i).onAnimationUpdate(this);
        }
    }
}

3. 插值器

从上面的介绍可以看到，Interpolator的关键是getInterpolation();

在ValueAnimator.animationFrame()中可以看到， 传递给Interpolator 的fraction是在[0,1] 值域范围。

float fraction = mDuration > 0 ? (float)(currentTime - mStartTime) / mDuration : 1f;
if (fraction >= 1f) {
    if (mCurrentIteration < mRepeatCount || mRepeatCount == INFINITE) {
        // Time to repeat
        if (mListeners != null) {
            int numListeners = mListeners.size();
            for (int i = 0; i < numListeners; ++i) {
                mListeners.get(i).onAnimationRepeat(this);
            }
        }
        if (mRepeatMode == REVERSE) {
            mPlayingBackwards = !mPlayingBackwards;
        }
        mCurrentIteration += (int)fraction;
        fraction = fraction % 1f;
        mStartTime += mDuration;
    } else {
        done = true;
        fraction = Math.min(fraction, 1.0f);
    }
}
if (mPlayingBackwards) {
    fraction = 1f - fraction;
}

所以设计Interpolator 就是设计一个输入[0,1] 的函数。

先参观一下系统的几个Interpolator。

3.1 AccelerateDecelerateInterpolator 

cos(t+1)Pi /2 +0.5f

从图可以看到，先加速后减速，病最终到达结束位置。

public class AccelerateDecelerateInterpolator implements Interpolator {
    public float getInterpolation(float input) {
        return (float)(Math.cos((input + 1) * Math.PI) / 2.0f) + 0.5f;
    }
}

3.2 AccelerateInterpolator 

如果factor=1 则函数为x^2

否则函数为x^a (a 是参数)

默认函数式x^2

如图示，逐渐加速到结束位置。

public class AccelerateInterpolator implements Interpolator {
    private final float mFactor;
    private final double mDoubleFactor;

    public AccelerateInterpolator() {
        mFactor = 1.0f;
        mDoubleFactor = 2.0;
    }

    /**
     * Constructor
     *
     * @param factor Degree to which the animation should be eased. Seting
     *        factor to 1.0f produces a y=x^2 parabola. Increasing factor above
     *        1.0f  exaggerates the ease-in effect (i.e., it starts even
     *        slower and ends evens faster)
     */
    public AccelerateInterpolator(float factor) {
        mFactor = factor;
        mDoubleFactor = 2 * mFactor;
    }

     public float getInterpolation(float input) {
        if (mFactor == 1.0f) {
            return input * input;
        } else {
            return (float)Math.pow(input, mDoubleFactor);
        }
    }
}

3.3 LinearInterpolator 

线性的就是Y=X 没啥说的。

public class LinearInterpolator implements Interpolator {
    public float getInterpolation(float input) {
        return input;
    }
}

3.4 anticipateInterpolator  

函数是：x^2((a+1)x-a) 默认参数a=2 默认函数为x^2(3x-1)

如图示， 会先反方向执行一段，然后正向一直加速至结束位置。

public class AnticipateInterpolator implements Interpolator {
    private final float mTension;

    public AnticipateInterpolator() {
        mTension = 2.0f;
    }

    /**
     * @param tension Amount of anticipation. When tension equals 0.0f, there is
     *                no anticipation and the interpolator becomes a simple
     *                acceleration interpolator.
     */
    public AnticipateInterpolator(float tension) {
        mTension = tension;
    }

    public float getInterpolation(float t) {
        // a(t) = t * t * ((tension + 1) * t - tension)
        return t * t * ((mTension + 1) * t - mTension);
    }
}

3.5 aniticipateOvershoot 

是一个分段函数，默认参数a=3

2x*x[(2x*(a+1)-a)]     0<=x<=0.5

2(x-1)(x-1)[(2x-1)(a+1)+a]    0.5<x<=1

通过下图可以看到，动画会先反方向执行，然后向正方向逐渐加速，在快结束时逐渐减速，并超过预设的值，最后回到结束位置。

2x*x[(2x*(a+1)-a)]     0<=x<=0.5 的函数图

2(x-1)(x-1)[(2x-1)(a+1)+a]    0.5<x<=1的函数图

public class AnticipateOvershootInterpolator implements Interpolator {
    private final float mTension;

    public AnticipateOvershootInterpolator() {
        mTension = 2.0f * 1.5f;
    }

    /**
     * @param tension Amount of anticipation/overshoot. When tension equals 0.0f,
     *                there is no anticipation/overshoot and the interpolator becomes
     *                a simple acceleration/deceleration interpolator.
     */
    public AnticipateOvershootInterpolator(float tension) {
        mTension = tension * 1.5f;
    }

    /**
     * @param tension Amount of anticipation/overshoot. When tension equals 0.0f,
     *                there is no anticipation/overshoot and the interpolator becomes
     *                a simple acceleration/deceleration interpolator.
     * @param extraTension Amount by which to multiply the tension. For instance,
     *                     to get the same overshoot as an OvershootInterpolator with
     *                     a tension of 2.0f, you would use an extraTension of 1.5f.
     */
    public AnticipateOvershootInterpolator(float tension, float extraTension) {
        mTension = tension * extraTension;
    }

    private static float a(float t, float s) {
        return t * t * ((s + 1) * t - s);
    }

    private static float o(float t, float s) {
        return t * t * ((s + 1) * t + s);
    }

    public float getInterpolation(float t) {
        // a(t, s) = t * t * ((s + 1) * t - s)
        // o(t, s) = t * t * ((s + 1) * t + s)
        // f(t) = 0.5 * a(t * 2, tension * extraTension), when t < 0.5
        // f(t) = 0.5 * (o(t * 2 - 2, tension * extraTension) + 2), when t <= 1.0
        if (t < 0.5f) return 0.5f * a(t * 2.0f, mTension);
        else return 0.5f * (o(t * 2.0f - 2.0f, mTension) + 2.0f);
    }
}

4. 指导设计动画。

从第3节中可以看到，想要让动画按照我们预期的行为来执行，需要做的就是找到合适的函数。

画图使用http://www.fooplot.com/在线工具