在frameworks/base/core/java/android/view/ViewRootImpl.java的performTraversals方法中完成View的Surface创建流程后继续进行绘制流程：
private void performTraversals() {
......
boolean cancelDraw = mAttachInfo.mTreeObserver.dispatchOnPreDraw() || !isViewVisible;
if (!cancelDraw) {
if (mPendingTransitions != null && mPendingTransitions.size() > 0) {
for (int i = 0; i < mPendingTransitions.size(); ++i) {
mPendingTransitions.get(i).startChangingAnimations();
}
mPendingTransitions.clear();
}
performDraw();
} else {
if (isViewVisible) {
// Try again
scheduleTraversals();
} else if (mPendingTransitions != null && mPendingTransitions.size() > 0) {
for (int i = 0; i < mPendingTransitions.size(); ++i) {
mPendingTransitions.get(i).endChangingAnimations();
}
mPendingTransitions.clear();
}
}
......
}
调用了ViewRootImpl的performDraw方法：
private void performDraw() {
......
try {
......
boolean canUseAsync = draw(fullRedrawNeeded);
......
}
......
}
调用了ViewRootImpl的draw方法：
private boolean draw(boolean fullRedrawNeeded) {
......
if (!dirty.isEmpty() || mIsAnimating || accessibilityFocusDirty) {
if (mAttachInfo.mThreadedRenderer != null && mAttachInfo.mThreadedRenderer.isEnabled()) {
......
mAttachInfo.mThreadedRenderer.draw(mView, mAttachInfo, this);
} else {
// If we get here with a disabled & requested hardware renderer, something went
// wrong (an invalidate posted right before we destroyed the hardware surface
// for instance) so we should just bail out. Locking the surface with software
// rendering at this point would lock it forever and prevent hardware renderer
// from doing its job when it comes back.
// Before we request a new frame we must however attempt to reinitiliaze the
// hardware renderer if it's in requested state. This would happen after an
// eglTerminate() for instance.
if (mAttachInfo.mThreadedRenderer != null &&
!mAttachInfo.mThreadedRenderer.isEnabled() &&
mAttachInfo.mThreadedRenderer.isRequested() &&
mSurface.isValid()) {
try {
mAttachInfo.mThreadedRenderer.initializeIfNeeded(
mWidth, mHeight, mAttachInfo, mSurface, surfaceInsets);
} catch (OutOfResourcesException e) {
handleOutOfResourcesException(e);
return false;
}
mFullRedrawNeeded = true;
scheduleTraversals();
return false;
}
if (!drawSoftware(surface, mAttachInfo, xOffset, yOffset,
scalingRequired, dirty, surfaceInsets)) {
return false;
}
}
}
if (animating) {
mFullRedrawNeeded = true;
scheduleTraversals();
}
return useAsyncReport;
}
如果是软件渲染，则调用了ViewRootImpl的drawSoftware方法：
/**
* @return true if drawing was successful, false if an error occurred
*/
private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff,
boolean scalingRequired, Rect dirty, Rect surfaceInsets) {
// Draw with software renderer.
final Canvas canvas;
......
try {
......
canvas = mSurface.lockCanvas(dirty);
......
}
......
try {
......
mView.draw(canvas);
drawAccessibilityFocusedDrawableIfNeeded(canvas);
} finally {
try {
surface.unlockCanvasAndPost(canvas);
}
......
}
return true;
}
如果是硬件渲染，则调用了frameworks/base/core/java/android/view/ThreadedRenderer.java的draw方法：
/**
* Draws the specified view.
*
* @param view The view to draw.
* @param attachInfo AttachInfo tied to the specified view.
*/
void draw(View view, AttachInfo attachInfo, DrawCallbacks callbacks) {
final Choreographer choreographer = attachInfo.mViewRootImpl.mChoreographer;
choreographer.mFrameInfo.markDrawStart();
updateRootDisplayList(view, callbacks); // 1.根据view构建DisplayList
// register animating rendernodes which started animating prior to renderer
// creation, which is typical for animators started prior to first draw
if (attachInfo.mPendingAnimatingRenderNodes != null) {
final int count = attachInfo.mPendingAnimatingRenderNodes.size();
for (int i = 0; i < count; i++) {
registerAnimatingRenderNode(
attachInfo.mPendingAnimatingRenderNodes.get(i)); // 2.注册动画渲染结点
}
attachInfo.mPendingAnimatingRenderNodes.clear();
// We don't need this anymore as subsequent calls to
// ViewRootImpl#attachRenderNodeAnimator will go directly to us.
attachInfo.mPendingAnimatingRenderNodes = null;
}
int syncResult = syncAndDrawFrame(choreographer.mFrameInfo); // 3.交给RenderThread渲染
if ((syncResult & SYNC_LOST_SURFACE_REWARD_IF_FOUND) != 0) {
Log.w("OpenGLRenderer", "Surface lost, forcing relayout");
// We lost our surface. For a relayout next frame which should give us a new
// surface from WindowManager, which hopefully will work.
attachInfo.mViewRootImpl.mForceNextWindowRelayout = true;
attachInfo.mViewRootImpl.requestLayout();
}
if ((syncResult & SYNC_REDRAW_REQUESTED) != 0) {
attachInfo.mViewRootImpl.invalidate(); // 4.以便线程信息同步
}
}
首先调用了ThreadedRenderer的updateRootDisplayList方法：
private void updateRootDisplayList(View view, DrawCallbacks callbacks) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "Record View#draw()");
updateViewTreeDisplayList(view);
// Consume and set the frame callback after we dispatch draw to the view above, but before
// onPostDraw below which may reset the callback for the next frame. This ensures that
// updates to the frame callback during scroll handling will also apply in this frame.
if (mNextRtFrameCallbacks != null) {
final ArrayList<FrameDrawingCallback> frameCallbacks = mNextRtFrameCallbacks;
mNextRtFrameCallbacks = null;
setFrameCallback(frame -> {
for (int i = 0; i < frameCallbacks.size(); ++i) {
frameCallbacks.get(i).onFrameDraw(frame);
}
});
}
if (mRootNodeNeedsUpdate || !mRootNode.hasDisplayList()) {
RecordingCanvas canvas = mRootNode.beginRecording(mSurfaceWidth, mSurfaceHeight);
try {
final int saveCount = canvas.save();
canvas.translate(mInsetLeft, mInsetTop);
callbacks.onPreDraw(canvas);
canvas.enableZ();
canvas.drawRenderNode(view.updateDisplayListIfDirty());
canvas.disableZ();
callbacks.onPostDraw(canvas);
canvas.restoreToCount(saveCount);
mRootNodeNeedsUpdate = false;
} finally {
mRootNode.endRecording();
}
}
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
调用了ThreadedRenderer的updateViewTreeDisplayList方法：
private void updateViewTreeDisplayList(View view) {
view.mPrivateFlags |= View.PFLAG_DRAWN;
view.mRecreateDisplayList = (view.mPrivateFlags & View.PFLAG_INVALIDATED)
== View.PFLAG_INVALIDATED;
view.mPrivateFlags &= ~View.PFLAG_INVALIDATED;
view.updateDisplayListIfDirty();
view.mRecreateDisplayList = false;
}
调用了frameworks/base/core/java/android/view/View.java的updateDisplayListIfDirty方法：
/**
* Gets the RenderNode for the view, and updates its DisplayList (if needed and supported)
* @hide
*/
@NonNull
@UnsupportedAppUsage
public RenderNode updateDisplayListIfDirty() {
final RenderNode renderNode = mRenderNode;
if (!canHaveDisplayList()) {
// can't populate RenderNode, don't try
return renderNode;
}
if ((mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == 0
|| !renderNode.hasDisplayList()
|| (mRecreateDisplayList)) {
// Don't need to recreate the display list, just need to tell our
// children to restore/recreate theirs
if (renderNode.hasDisplayList()
&& !mRecreateDisplayList) {
mPrivateFlags |= PFLAG_DRAWN | PFLAG_DRAWING_CACHE_VALID;
mPrivateFlags &= ~PFLAG_DIRTY_MASK;
dispatchGetDisplayList();
return renderNode; // no work needed
}
// If we got here, we're recreating it. Mark it as such to ensure that
// we copy in child display lists into ours in drawChild()
mRecreateDisplayList = true;
int width = mRight - mLeft;
int height = mBottom - mTop;
int layerType = getLayerType();
final RecordingCanvas canvas = renderNode.beginRecording(width, height);
try {
if (layerType == LAYER_TYPE_SOFTWARE) {
buildDrawingCache(true);
Bitmap cache = getDrawingCache(true);
if (cache != null) {
canvas.drawBitmap(cache, 0, 0, mLayerPaint);
}
} else {
computeScroll();
canvas.translate(-mScrollX, -mScrollY);
mPrivateFlags |= PFLAG_DRAWN | PFLAG_DRAWING_CACHE_VALID;
mPrivateFlags &= ~PFLAG_DIRTY_MASK;
// Fast path for layouts with no backgrounds
if ((mPrivateFlags & PFLAG_SKIP_DRAW) == PFLAG_SKIP_DRAW) {
dispatchDraw(canvas);
drawAutofilledHighlight(canvas);
if (mOverlay != null && !mOverlay.isEmpty()) {
mOverlay.getOverlayView().draw(canvas);
}
if (isShowingLayoutBounds()) {
debugDrawFocus(canvas);
}
} else {
draw(canvas);
}
}
} finally {
renderNode.endRecording();
setDisplayListProperties(renderNode);
}
} else {
mPrivateFlags |= PFLAG_DRAWN | PFLAG_DRAWING_CACHE_VALID;
mPrivateFlags &= ~PFLAG_DIRTY_MASK;
}
return renderNode;
}
每一次调用canvas.draw方法，就录制了一次绘图操作，即为displayList增加了一个元素。
至此，displayList构建完成，在rootRenderNode中，递归包含了所有子view的displayList。
displayList的构建是在主线程中进行的，接下来将在渲染线程（RenderThread）中对displayList进行绘制。
回到ThreadedRenderer的draw方法中，在displayList构建完成后，还调用了其父类frameworks/base/graphics/java/android/graphics/HardwareRenderer.java的syncAndDrawFrame方法：
/**
* Syncs the RenderNode tree to the render thread and requests a frame to be drawn.
*
* @hide
*/
@SyncAndDrawResult
public int syncAndDrawFrame(@NonNull FrameInfo frameInfo) {
return nSyncAndDrawFrame(mNativeProxy, frameInfo.frameInfo, frameInfo.frameInfo.length);
}
其中nSyncAndDrawFrame是frameworks/base/libs/hwui/jni/android_graphics_HardwareRenderer.cpp中的android_view_ThreadedRenderer_syncAndDrawFrame方法：
static int android_view_ThreadedRenderer_syncAndDrawFrame(JNIEnv* env, jobject clazz,
jlong proxyPtr, jlongArray frameInfo, jint frameInfoSize) {
LOG_ALWAYS_FATAL_IF(frameInfoSize != UI_THREAD_FRAME_INFO_SIZE,
"Mismatched size expectations, given %d expected %d",
frameInfoSize, UI_THREAD_FRAME_INFO_SIZE);
RenderProxy* proxy = reinterpret_cast<RenderProxy*>(proxyPtr);
env->GetLongArrayRegion(frameInfo, 0, frameInfoSize, proxy->frameInfo());
return proxy->syncAndDrawFrame();
}
调用了frameworks/base/libs/hwui/renderthread/RenderProxy.cpp的syncAndDrawFrame方法：
int RenderProxy::syncAndDrawFrame() {
return mDrawFrameTask.drawFrame();
}
调用了frameworks/base/libs/hwui/renderthread/DrawFrameTask.cpp的drawFrame方法：
int DrawFrameTask::drawFrame() {
LOG_ALWAYS_FATAL_IF(!mContext, "Cannot drawFrame with no CanvasContext!");
mSyncResult = SyncResult::OK;
mSyncQueued = systemTime(SYSTEM_TIME_MONOTONIC);
postAndWait();
return mSyncResult;
}
调用了DrawFrameTask的postAndWait方法：
void DrawFrameTask::postAndWait() {
AutoMutex _lock(mLock);
mRenderThread->queue().post([this]() { run(); });
mSignal.wait(mLock);
}
接下来切换到渲染线程RenderThread中执行DrawFrameTask的run方法：
void DrawFrameTask::run() {
ATRACE_NAME("DrawFrame");
bool canUnblockUiThread;
bool canDrawThisFrame;
{
TreeInfo info(TreeInfo::MODE_FULL, *mContext);
canUnblockUiThread = syncFrameState(info);
canDrawThisFrame = info.out.canDrawThisFrame;
if (mFrameCompleteCallback) {
mContext->addFrameCompleteListener(std::move(mFrameCompleteCallback));
mFrameCompleteCallback = nullptr;
}
}
// Grab a copy of everything we need
CanvasContext* context = mContext;
std::function<void(int64_t)> callback = std::move(mFrameCallback);
mFrameCallback = nullptr;
// From this point on anything in "this" is *UNSAFE TO ACCESS*
if (canUnblockUiThread) {
unblockUiThread();
}
// Even if we aren't drawing this vsync pulse the next frame number will still be accurate
if (CC_UNLIKELY(callback)) {
context->enqueueFrameWork(
[callback, frameNr = context->getFrameNumber()]() { callback(frameNr); });
}
if (CC_LIKELY(canDrawThisFrame)) {
context->draw();
} else {
// wait on fences so tasks don't overlap next frame
context->waitOnFences();
}
if (!canUnblockUiThread) {
unblockUiThread();
}
}
更细节的绘制流程见HWUI绘制流程