Android 動畫animation 深入分析
前言：本文試圖通過分析動畫流程，來理解android動畫系統的設計與實現，學習動畫的基本原則，最終希望能夠指導動畫的設計。
0 本文中用到的一些類圖
1 view animation
調用方法：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);
}
即調用parent的invalidateChild，
假定父控件即為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) {
//...省略一堆判斷條件，最終調用
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();是設置同步障礙（syncBarrier），當looper中的消息隊列執行到barrier 後，會暫停執行，隻有當barrier 被釋放mHandler.getLooper().removeSyncBarrier(mTraversalBarrier); 後消息隊列才能繼續執行。
Choreographer mChoreographer; 是動畫系統中的核心組織者， 負責統一調度。後面詳細說。
final TraversalRunnable mTraversalRunnable = new TraversalRunnable();
final class TraversalRunnable implements Runnable {
@Override
public void run() {
doTraversal();
}
}
void doTraversal() {
performTraversals();
}
perform 待補充
final class ConsumeBatchedInputRunnable implements Runnable {
@Override
public void run() {
doConsumeBatchedInput(mChoreographer.getFrameTimeNanos());
}
}
final ConsumeBatchedInputRunnable mConsumedBatchedInputRunnable =
new ConsumeBatchedInputRunnable();
doConsume 待補充
2 屬性動畫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();
}
這裡會檢查調用線程必須是Looper線程，如果是view相關的屬性動畫，還必須是UI 線程。
得到AnimationHandle 並把自己加入到PendingAnimations 的list中.
getOrCreateAnimationHandler();
protected static ThreadLocal sAnimationHandler =
new ThreadLocal()
protected static class AnimationHandler implements Runnable {
// The per-thread list of all active animations
/** @hide */
protected final ArrayList mAnimations = new ArrayList();
// Used in doAnimationFrame() to avoid concurrent modifications of mAnimations
private final ArrayList mTmpAnimations = new ArrayList();
// The per-thread set of animations to be started on the next animation frame
/** @hide */
protected final ArrayList mPendingAnimations = new ArrayList();
/**
* Internal per-thread collections used to avoid set collisions as animations start and end
* while being processed.
* @hide
*/
protected final ArrayList mDelayedAnims = new ArrayList();
private final ArrayList mEndingAnims = new ArrayList();
private final ArrayList mReadyAnims = new ArrayList();
private final Choreographer mChoreographer;
private boolean mAnimationScheduled;
}
AnimationHandler 就是一個runnable， 註意成員變量中的多個animator 的list 以及重要的mChoreographer = Choreographer.getInstance();
mChoreographer 也是一個threadlocal的變量。
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 的隊列中。
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);
}
}
}
傳入的delay為0， 即調用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 默認是true；
private boolean isRunningOnLooperThreadLocked() {
return Looper.myLooper() == mLooper;
}
檢查當前looper和mChoreographer的looper是否一致。一般情況是一致的。就會調用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);
}
}
到瞭native 暫時先不涉及。
回頭來看animationHandler 的run()。 前面提到animationHandler把自己添加到mChoreographer，當被調用時，調用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()總結就是
1.遍歷pending list動畫，如果delay為0 則調用start，不為0，加入delay list；
2.遍歷delay list， 根據frametime計算是繼續delay還是ready可以播放，若是ready，則加入到ready list中；
3 遍歷ready list，調用start ；
4，遍歷所有animation，根據frametime計算動畫是否要結束，如果可以結束，則加入到ending list中；
5，遍歷ending list， 調用end；
6， 如果有列表中仍然有動畫，則繼續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 pendingCopy =
(ArrayList) 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() 中根據當前狀態，並且計算fraction，調用animateValue();
boolean animationFrame(long currentTime) {
boolean done = false;
switch (mPlayingState) {
case RUNNING:
case SEEKED:
//省略計算fraction的代碼
animateValue(fraction);
break;
}
return done;
}
通過mInterpolator.getInterpolation計算fraction；@Interpolator
根據fraction計算內部所有value，如果有updateListener，調用之。
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
從上面的介紹可以看到，Interpolator的關鍵是getInterpolation();
在ValueAnimator.animationFrame()中可以看到， 傳遞給Interpolator 的fraction是在[0,1] 值域范圍。
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;
}
所以設計Interpolator 就是設計一個輸入[0,1] 的函數。
先參觀一下系統的幾個Interpolator。
3.1 AccelerateDecelerateInterpolator
cos(t+1)Pi /2 +0.5f
從圖可以看到，先加速後減速，病最終到達結束位置。
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 則函數為x^2
否則函數為x^a (a 是參數)
默認函數式x^2
如圖示，逐漸加速到結束位置。
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
線性的就是Y=X 沒啥說的。
public class LinearInterpolator implements Interpolator {
public float getInterpolation(float input) {
return input;
}
}
3.4 anticipateInterpolator
函數是：x^2((a+1)x-a) 默認參數a=2 默認函數為x^2(3x-1)
如圖示， 會先反方向執行一段，然後正向一直加速至結束位置。
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
是一個分段函數，默認參數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
</x<=1
通過下圖可以看到，動畫會先反方向執行，然後向正方向逐漸加速，在快結束時逐漸減速，並超過預設的值，最後回到結束位置。
2x*x[(2x*(a+1)-a)] 0<=x<=0.5 的函數圖
2(x-1)(x-1)[(2x-1)(a+1)+a] 0.5<x<=1的函數圖
</x<=1的函數圖
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. 指導設計動畫。
從第3節中可以看到，想要讓動畫按照我們預期的行為來執行，需要做的就是找到合適的函數。