前言今天继续屏幕刷新机制的知识讲解，上文说到 代码未动，图先行
UI变化上期说到app并不是每一个 那我们就从有绘制需求开始看，当我们修改了UI后，都会执行 可以看到，最后会调用到父布局 public ViewRootImpl(Context context, Display display) {
//...
mChoreographer = Choreographer.getInstance();
}
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
//...
}
}为了方便查看，我只留了相关代码。可以看到，在 Choreographer实例化//Choreographer.java
public static Choreographer getInstance() {
return sThreadInstance.get();
}
private static final ThreadLocal<Choreographer> sThreadInstance =
new ThreadLocal<Choreographer>() {
@Override
protected Choreographer initialValue() {
Looper looper = Looper.myLooper();
//...
Choreographer choreographer = new Choreographer(looper, VSYNC_SOURCE_APP);
//...
return choreographer;
}
};
private Choreographer(Looper looper, int vsyncSource) {
mLooper = looper;
mHandler = new FrameHandler(looper);
//初始化FrameDisplayEventReceiver
mDisplayEventReceiver = USE_VSYNC
? new FrameDisplayEventReceiver(looper, vsyncSource)
: null;
mLastFrameTimeNanos = Long.MIN_VALUE;
//一帧间隔时间
mFrameIntervalNanos = (long)(1000000000 / getRefreshRate());
mCallbackQueues = new CallbackQueue[CALLBACK_LAST + 1];
for (int i = 0; i <= CALLBACK_LAST; i++) {
mCallbackQueues[i] = new CallbackQueue();
}
}ThreadLocal，是不是有点熟悉？之前说Handler的时候说过，Handler是怎么获取当前线程的Looper的？就是通过这个 存储方法还是一样，以 所以这里创建的mHandler就是 postCallback private void postCallbackDelayedInternal(int callbackType,
Object action, Object token, long delayMillis) {
if (DEBUG_FRAMES) {
Log.d(TAG, "PostCallback: type=" + callbackType
+ ", action=" + action + ", token=" + token
+ ", delayMillis=" + 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);
}
}
}
private final class FrameHandler extends Handler {
public FrameHandler(Looper looper) {
super(looper);
}
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MSG_DO_FRAME:
doFrame(System.nanoTime(), 0);
break;
case MSG_DO_SCHEDULE_VSYNC:
doScheduleVsync();
break;
case MSG_DO_SCHEDULE_CALLBACK:
doScheduleCallback(msg.arg1);
break;
}
}
}
void doScheduleCallback(int callbackType) {
synchronized (mLock) {
if (!mFrameScheduled) {
final long now = SystemClock.uptimeMillis();
if (mCallbackQueues[callbackType].hasDueCallbacksLocked(now)) {
scheduleFrameLocked(now);
}
}
}
}在 然后判断设定的时间是否在当前时间之后，也就是有没有延迟，如果有延迟就发送延迟消息消息 scheduleFrameLocked（准备申请VSYNC信号） private void scheduleFrameLocked(long now) {
if (!mFrameScheduled) {
mFrameScheduled = true;
if (USE_VSYNC) {
//是否运行在主线程
if (isRunningOnLooperThreadLocked()) {
scheduleVsyncLocked();
} else {
//通过Handler切换线程
Message msg = mHandler.obtainMessage(MSG_DO_SCHEDULE_VSYNC);
msg.setAsynchronous(true);
mHandler.sendMessageAtFrontOfQueue(msg);
}
} else {
//计算下一帧的时间
final long nextFrameTime = Math.max(
mLastFrameTimeNanos / TimeUtils.NANOS_PER_MS + sFrameDelay, now);
Message msg = mHandler.obtainMessage(MSG_DO_FRAME);
msg.setAsynchronous(true);
mHandler.sendMessageAtTime(msg, nextFrameTime);
}
}
}
case MSG_DO_FRAME:
doFrame(System.nanoTime(), 0);
break;
case MSG_DO_SCHEDULE_VSYNC:
doScheduleVsync();
break;
void doScheduleVsync() {
synchronized (mLock) {
if (mFrameScheduled) {
scheduleVsyncLocked();
}
}
}该方法中，首先判断了是否开启了 如果没有开启 另外可以看到，刚才我们用到Handler发送消息的时候，都调用了 小结1通过上面一系列方法，我们能得到一个初步的逻辑过程了：
在这个过程中， 继续看 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);
}
}代码很简单，就是通过 这个 刚才说到调用 onVsync（接收VSYNC信号） private final class FrameDisplayEventReceiver extends DisplayEventReceiver
implements Runnable {
@Override
public void onVsync(long timestampNanos, long physicalDisplayId, int frame) {
//...
mTimestampNanos = timestampNanos;
mFrame = frame;
Message msg = Message.obtain(mHandler, this);
msg.setAsynchronous(true);
mHandler.sendMessageAtTime(msg, timestampNanos / TimeUtils.NANOS_PER_MS);
}
@Override
public void run() {
mHavePendingVsync = false;
doFrame(mTimestampNanos, mFrame);
}
}这里同样通过Handler发送了一条消息，执行了本身的 doFrame（绘制帧数据） void doFrame(long frameTimeNanos, int frame) {
final long startNanos;
synchronized (mLock) {
//...
//当前帧的vsync信号来的时间，假如为12分200ms
long intendedFrameTimeNanos = frameTimeNanos;
//当前时间，也就是开始绘制的时间,假如为12分150ms
startNanos = System.nanoTime();
//计算时间差，如果大于一个帧时间，则是跳帧了。比如是50ms，大于16ms
final long jitterNanos = startNanos - frameTimeNanos;
if (jitterNanos >= mFrameIntervalNanos) {
//计算掉了几帧，50/16=3帧
final long skippedFrames = jitterNanos / mFrameIntervalNanos;
//计算一帧内时间差，50%16=2ms
final long lastFrameOffset = jitterNanos % mFrameIntervalNanos;
//修正时间,vsync信号应该来得时间，为12分148ms，保证和绘制时间对应上
frameTimeNanos = startNanos - lastFrameOffset;
}
if (frameTimeNanos < mLastFrameTimeNanos) {
//信号时间已过，不能再绘制了，等待下一个vsync信号，保证后续时间同步上
scheduleVsyncLocked();
return;
}
mFrameScheduled = false;
mLastFrameTimeNanos = frameTimeNanos;
}
try {
//执行相关的callback任务
mFrameInfo.markInputHandlingStart();
doCallbacks(Choreographer.CALLBACK_INPUT, frameTimeNanos);
mFrameInfo.markAnimationsStart();
doCallbacks(Choreographer.CALLBACK_ANIMATION, frameTimeNanos);
doCallbacks(Choreographer.CALLBACK_INSETS_ANIMATION, frameTimeNanos);
mFrameInfo.markPerformTraversalsStart();
doCallbacks(Choreographer.CALLBACK_TRAVERSAL, frameTimeNanos);
doCallbacks(Choreographer.CALLBACK_COMMIT, frameTimeNanos);
} finally {
AnimationUtils.unlockAnimationClock();
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}这里主要的工作就是：
doCallbacks（执行任务） void doCallbacks(int callbackType, long frameTimeNanos) {
CallbackRecord callbacks;
synchronized (mLock) {
final long now = System.nanoTime();
callbacks = mCallbackQueues[callbackType].extractDueCallbacksLocked(
now / TimeUtils.NANOS_PER_MS);
if (callbacks == null) {
return;
}
mCallbacksRunning = true;
if (callbackType == Choreographer.CALLBACK_COMMIT) {
final long jitterNanos = now - frameTimeNanos;
Trace.traceCounter(Trace.TRACE_TAG_VIEW, "jitterNanos", (int) jitterNanos);
if (jitterNanos >= 2 * mFrameIntervalNanos) {
final long lastFrameOffset = jitterNanos % mFrameIntervalNanos
+ mFrameIntervalNanos;
frameTimeNanos = now - lastFrameOffset;
mLastFrameTimeNanos = frameTimeNanos;
}
}
}
try {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, CALLBACK_TRACE_TITLES[callbackType]);
for (CallbackRecord c = callbacks; c != null; c = c.next) {
c.run(frameTimeNanos);
}
} finally {
synchronized (mLock) {
mCallbacksRunning = false;
do {
final CallbackRecord next = callbacks.next;
recycleCallbackLocked(callbacks);
callbacks = next;
} while (callbacks != null);
}
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}
private static final class CallbackRecord {
public CallbackRecord next;
public long dueTime;
public Object action; // Runnable or FrameCallback
public Object token;
@UnsupportedAppUsage
public void run(long frameTimeNanos) {
if (token == FRAME_CALLBACK_TOKEN) {
((FrameCallback)action).doFrame(frameTimeNanos);
} else {
((Runnable)action).run();
}
}
}其实就是按类型，从 而这个run方法中，判断了token，并执行了 mChoreographer.postCallback( Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null); token为空，所以会执行到action也就是 所以兜兜转转，又回到了 最后看看 mTraversalRunnable final class TraversalRunnable implements Runnable {
@Override
public void run() {
doTraversal();
}
}
void doTraversal() {
if (mTraversalScheduled) {
mTraversalScheduled = false;
mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);
if (mProfile) {
Debug.startMethodTracing("ViewAncestor");
}
performTraversals();
if (mProfile) {
Debug.stopMethodTracing();
mProfile = false;
}
}
}这就很熟悉了吧，调用了 总结最后再看看总结图：
参考https:///post/6863756420380196877 拜拜 |
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