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在《浅析Android中View的测量布局流程》中我们对VSYNC信号到达App进程之后开启的View布局过程进行了分析#xff0c;经过对整个App界面的View树进行遍历完成了测量和布局#xff0c;确定了View的大小以及在屏幕中所处的位置。但是#xff0c;如果想让用户在屏幕上看到…前言
在《浅析Android中View的测量布局流程》中我们对VSYNC信号到达App进程之后开启的View布局过程进行了分析经过对整个App界面的View树进行遍历完成了测量和布局确定了View的大小以及在屏幕中所处的位置。但是如果想让用户在屏幕上看到View的内容还需要根据View的绘制生成图形数据并交由硬件进行屏幕刷新。
View的绘制主要负责将业务层的各种API调用转换为指令然后交给渲染引擎进行处理最终生成能够被硬件直接处理的数据。这个过程主要分为渲染数据的生产以及消费一般来说渲染数据的生产者是各个App进程而消费者则是SurfaceFlinger进程这里会涉及到渲染数据的跨进程传输问题。下面将会对渲染数据的跨进程传输的实现进行分析。
Surface作为数据载体负责打通App进程与SurfaceFlinger进程之间的数据交互同时Surface是属于App进程内的资源因此先从App进程这个生产者出发基于Surface的创建流程及其使用对渲染数据的传递机制进行分析。
绘制前的准备
在《浅析Android中View的测量布局流程》中有分析到当测量数据发生变化时需要对窗体大小进行更新因为测量数据的变化导致视图展示区域随之发生变化。
根据分析测量布局流程的相关源码实现可知一个ViewRootImpl对象被创建时都会创建一个Surface对象以及SurfaceControl对象但是Surface对象并不是立即可用于绘制渲染的而只是一个壳子其真正的实现是在native层。而在测量之后宽高如果发生变化则需要对窗口大小进行更新此时会对Surface以及SurfaceControl对象进行处理即更新native层的Surface以及SurfaceControl对象之后Surface对象将进入可用状态。
SurfaceControl的创建
首先App进程为每一个Activity创建了一个Window而每一个Window会对应一个ViewRootImpl每一个ViewRootImpl持有一个Surface以及SurfaceControl对象。然后SystemServer进程会对应地为App进程的每一个Window创建一个Window相对应地也会为每一个Window创建一个SurfaceControl对象。下面我们看下SystemServer进程中的SurfaceControl的创建过程。
public final class ViewRootImpl implements ViewParent, View.AttachInfo.Callbacks, ThreadedRenderer.DrawCallbacks, AttachedSurfaceControl {final W mWindow; // mWindow new W(this);public final Surface mSurface new Surface();private final SurfaceControl mSurfaceControl new SurfaceControl();// ...private void performTraversals() {// ...boolean windowShouldResize layoutRequested windowSizeMayChange ((mWidth ! host.getMeasuredWidth() || mHeight ! host.getMeasuredHeight()) || (lp.width ViewGroup.LayoutParams.WRAP_CONTENT frame.width() desiredWindowWidth frame.width() ! mWidth) || (lp.height ViewGroup.LayoutParams.WRAP_CONTENT frame.height() desiredWindowHeight frame.height() ! mHeight));// ...if (mFirst || windowShouldResize || viewVisibilityChanged || params ! null || mForceNextWindowRelayout) {try {// ...// 更新windowrelayoutResult relayoutWindow(params, viewVisibility, insetsPending);// ...} catch (RemoteException e) {} finally {// ...}}// ...}private int relayoutWindow(WindowManager.LayoutParams params, int viewVisibility, boolean insetsPending) throws RemoteException {// ...if (LOCAL_LAYOUT) {// ...} else {// mWindowSession是IWindowSession类型的对象即Binder代理对象对应实现是SystemServer进程中的Session类的实例每个进程的IWindowSession对应SystemServer进程中一个Session实例relayoutResult mWindowSession.relayout(mWindow, params, requestedWidth, requestedHeight, viewVisibility, insetsPending ? WindowManagerGlobal.RELAYOUT_INSETS_PENDING : 0, mTmpFrames, mPendingMergedConfiguration, mSurfaceControl, mTempInsets, mTempControls, mRelayoutBundle);// ...}// ...// mSurfaceControl实例可用之后根据mSurfaceControl的Surface信息对mSurface进行更新if (mSurfaceControl.isValid()) {if (!useBLAST()) {mSurface.copyFrom(mSurfaceControl);} else {updateBlastSurfaceIfNeeded();}// ...} else {// ...}// ...return relayoutResult;}// ...
}relayoutWindow方法会通过Binder请求到SystemServer进程对之前SystemServer进程中创建的window实例进行更新。mWindowSession.relayout会调用到WindowManagerService中的相关逻辑经过relayout方法调用了WindowManagerService#createSurfaceControl方法完成SystemServer进程中SurfaceControl对象的创建。
从SystemServer进程返回之后通过getSurfaceControl方法将新创建的SurfaceControl对象的属性拷贝回App进程的SurfaceControl对象即ViewRootImpl#mSurfaceControl中。
// com.android.server.wm.Session
/*** Session代表一个活跃的客户端session。SystemServer进程中会为每个进程维护一个Session对象用于window相关的Binder通信。*/
class Session extends IWindowSession.Stub implements IBinder.DeathRecipient {// ...Overridepublic int relayout(IWindow window, WindowManager.LayoutParams attrs, int requestedWidth, int requestedHeight, int viewFlags, int flags, int seq, int lastSyncSeqId, ClientWindowFrames outFrames, MergedConfiguration mergedConfiguration, SurfaceControl outSurfaceControl, InsetsState outInsetsState, InsetsSourceControl.Array outActiveControls, Bundle outSyncSeqIdBundle) {// ...int res mService.relayoutWindow(this, window, attrs, requestedWidth, requestedHeight, viewFlags, flags, seq, lastSyncSeqId, outFrames, mergedConfiguration, outSurfaceControl, outInsetsState, outActiveControls, outSyncSeqIdBundle);// ...return res;}// ...
}// com.android.server.wm.WindowManagerService
public class WindowManagerService extends IWindowManager.Stub implements Watchdog.Monitor, WindowManagerPolicy.WindowManagerFuncs {// ...public int relayoutWindow(Session session, IWindow client, LayoutParams attrs, int requestedWidth, int requestedHeight, int viewVisibility, int flags, int seq, int lastSyncSeqId, ClientWindowFrames outFrames, MergedConfiguration outMergedConfiguration, SurfaceControl outSurfaceControl, InsetsState outInsetsState, InsetsSourceControl.Array outActiveControls, Bundle outSyncIdBundle) {// ...synchronized (mGlobalLock) {// 获取窗体状态描述每一个Window通常对应一个Activity都对应一个WindowState。final WindowState win windowForClientLocked(session, client, false);// 获取WindowStateAnimator用于创建SurfaceControlWindowStateAnimator winAnimator win.mWinAnimator;// ...// 只有view可见或者相关联的appToken没有隐藏时才应该relayout。final boolean shouldRelayout viewVisibility View.VISIBLE (win.mActivityRecord null || win.mAttrs.type TYPE_APPLICATION_STARTING || win.mActivityRecord.isClientVisible());// ...if (shouldRelayout outSurfaceControl ! null) {try {// 创建SurfaceControl并将其拷贝到outSurfaceControloutSurfaceControlresult createSurfaceControl(outSurfaceControl, result, win, winAnimator);} catch (Exception e) {// ...return 0;}}// ...}// ...return result;}private int createSurfaceControl(SurfaceControl outSurfaceControl, int result, WindowState win, WindowStateAnimator winAnimator) {if (!win.mHasSurface) {result | RELAYOUT_RES_SURFACE_CHANGED;}WindowSurfaceController surfaceController;try {// 1. 通过WindowStateAnimator对象创建WindowSurfaceController对象surfaceController winAnimator.createSurfaceLocked();} finally {// ...}if (surfaceController ! null) {// 2. 通过WindowSurfaceController将SurfaceController拷贝到outSurfaceControl中outSurfaceControl对应App进程中的ViewRootImpl的mSurfaceControl变量surfaceController.getSurfaceControl(outSurfaceControl); } else {// ...outSurfaceControl.release();}return result;}// ...
}/*** 为单个WindowState跟踪动画和surface的操作.**/// com.android.server.wm.WindowStateAnimator
class WindowStateAnimator {final WindowState mWin;WindowSurfaceController mSurfaceController;// 创建WindowSurfaceControllerWindowSurfaceController createSurfaceLocked() {final WindowState w mWin;// 如果已经创建过就不会重复创建了if (mSurfaceController ! null) {return mSurfaceController;}try {// ...mSurfaceController new WindowSurfaceController(attrs.getTitle().toString(), format, flags, this, attrs.type);// ...} catch (OutOfResourcesException e) {// ...return null;} catch (Exception e) {// ...return null;}// ...return mSurfaceController;}// ...
}// com.android.server.wm.WindowSurfaceController
class WindowSurfaceController {WindowSurfaceController(String name, int format, int flags, WindowStateAnimator animator, int windowType) {// ...final SurfaceControl.Builder b win.makeSurface().setParent(win.getSurfaceControl()).setName(name).setFormat(format).setFlags(flags).setMetadata(METADATA_WINDOW_TYPE, windowType).setMetadata(METADATA_OWNER_UID, mWindowSession.mUid).setMetadata(METADATA_OWNER_PID, mWindowSession.mPid).setCallsite(WindowSurfaceController);// ...mSurfaceControl b.build();}public static class Builder {NonNullpublic SurfaceControl build() {// ....return new SurfaceControl(mSession, mName, mWidth, mHeight, mFormat, mFlags, mParent, mMetadata, mLocalOwnerView, mCallsite);}}
}可以看出WindowSurfaceController是SurfaceControl的包装类通过持有SurfaceControl对象来对Surface进行操作WindowSurfaceController以及SurfaceControl都是在SystemServer进程创建的。接下来继续跟着SurfaceControl的构造函数看下SurfaceControl的创建具体做了哪些事情。
/*** 持有一个由系统合成器管理的Surface对象。这个SurfaceControl对象由buffer以及如何显示buffer的信息组成。* 通过构造的Surface对象可以提交数据到buffer用于合成上屏。*/
public final class SurfaceControl implements Parcelable {public long mNativeObject;private long mNativeHandle;private SurfaceControl(SurfaceSession session, String name, int w, int h, int format, int flags, SurfaceControl parent, SparseIntArray metadata, WeakReferenceView localOwnerView, String callsite) throws OutOfResourcesException, IllegalArgumentException {// ...long nativeObject 0;try {// ...nativeObject nativeCreate(session, name, w, h, format, flags, parent ! null ? parent.mNativeObject : 0, metaParcel);} finally {metaParcel.recycle();}// ...assignNativeObject(nativeObject, callsite);// ...}private static native long nativeCreate(SurfaceSession session, String name, int w, int h, int format, int flags, long parentObject, Parcel metadata) throws OutOfResourcesException;private void assignNativeObject(long nativeObject, String callsite) {if (mNativeObject ! 0) {release();}if (nativeObject ! 0) {mFreeNativeResources sRegistry.registerNativeAllocation(this, nativeObject);}// 记录native层Surface对象的句柄值mNativeObject nativeObject;mNativeHandle mNativeObject ! 0 ? nativeGetHandle(nativeObject) : 0;if (sDebugUsageAfterRelease mNativeObject 0) {mReleaseStack new Throwable(Assigned invalid nativeObject);} else {mReleaseStack null;}setUnreleasedWarningCallSite(callsite);addToRegistry();}
}从源码可以看出Java层的SurfaceControl对象其实是一个壳其内部的主要实现是在native层的SurfaceControl对象中的通过持有native层的SurfaceControl对象的句柄值对其进行调用。因此SurfaceControl的关键实现在nativeCreate这个native方法中。
// frameworks/base/core/jni/android_view_SurfaceControl.cpp
static jlong nativeCreate(JNIEnv* env, jclass clazz, jobject sessionObj, jstring nameStr, jint w, jint h, jint format, jint flags, jlong parentObject, jobject metadataParcel) {// 获取SurfaceComposerClient对象SurfaceComposerClient对象负责与SurfaceFlinger进程进行交互spSurfaceComposerClient client;if (sessionObj ! NULL) {client android_view_SurfaceSession_getClient(env, sessionObj);} else {client SurfaceComposerClient::getDefault();}SurfaceControl *parent reinterpret_castSurfaceControl*(parentObject);spSurfaceControl surface;// ...// 创建SurfaceControl对象status_t err client-createSurfaceChecked(String8(name.c_str()), w, h, format, surface, flags, parentHandle, std::move(metadata));if (err NAME_NOT_FOUND) {jniThrowException(env, java/lang/IllegalArgumentException, NULL);return 0;} else if (err ! NO_ERROR) {jniThrowException(env, OutOfResourcesException, statusToString(err).c_str());return 0;}surface-incStrong((void *)nativeCreate);return reinterpret_castjlong(surface.get());
}从源码中得知通过SurfaceComposerClient调用createSurfaceChecked方法进行native层的SurfaceControl的创建内部通过成员变量mClient跨进程调用到SurfaceFlinger进程mClient的远程实现是SurfaceFlinger进程的Client类。
// frameworks/native/libs/gui/SurfaceComposerClient.cpp
status_t SurfaceComposerClient::createSurfaceChecked(const String8 name, uint32_t w, uint32_t h, PixelFormat format, spSurfaceControl* outSurface, int32_t flags, const spIBinder parentHandle, LayerMetadata metadata, uint32_t* outTransformHint) {status_t err mStatus;if (mStatus NO_ERROR) {gui::CreateSurfaceResult result;// 请求SurfaceFlinger进程创建一个SurfaceControlbinder::Status status mClient-createSurface(std::string(name.c_str()), flags, parentHandle, std::move(metadata), result);err statusTFromBinderStatus(status);// ... if (err NO_ERROR) {// 根据CreateSurfaceResult构造SurfaceControl对象并将其返回// result.handle是一个Binder对象封装了SurfaceFlinger进程的Layer以及SurfaceFlinger*outSurface new SurfaceControl(this, result.handle, result.layerId, toString(result.layerName), w, h, format, result.transformHint, flags);}}return err;
}// frameworks/native/libs/gui/SurfaceControl.cpp
SurfaceControl::SurfaceControl(const spSurfaceComposerClient client, const spIBinder handle, int32_t layerId, const std::string name, uint32_t w, uint32_t h, PixelFormat format, uint32_t transform, uint32_t flags): mClient(client),mHandle(handle),mLayerId(layerId),mName(name),mTransformHint(transform),mWidth(w),mHeight(h),mFormat(format),mCreateFlags(flags) {}SurfaceFlinger进程调用Client::createSurface创建Surface对象并根据方法的返回结果构造了SystemServer进程的SurfaceControl对象并将其返回最终拷贝回App进程的SurfaceControl对象即ViewRootImpl#mSurfaceControl。
但是到这里其实并没有发现跨进程传输数据相关的代码实现因此只能继续看下SurfaceFlinger进程的Client::createSurface方法具体做了什么事情。
// frameworks/native/services/surfaceflinger/Client.cpp
binder::Status Client::createSurface(const std::string name, int32_t flags, const spIBinder parent, const gui::LayerMetadata metadata, gui::CreateSurfaceResult* outResult) {spIBinder handle;LayerCreationArgs args(mFlinger.get(), spClient::fromExisting(this), name.c_str(), static_castuint32_t(flags), std::move(metadata));args.parentHandle parent;// 为App进程的SurfaceControl创建Layerconst status_t status mFlinger-createLayer(args, *outResult);return binderStatusFromStatusT(status);
}// frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
status_t SurfaceFlinger::createLayer(LayerCreationArgs args, gui::CreateSurfaceResult outResult) {status_t result NO_ERROR;spLayer layer;switch (args.flags ISurfaceComposerClient::eFXSurfaceMask) {case ISurfaceComposerClient::eFXSurfaceBufferQueue:case ISurfaceComposerClient::eFXSurfaceContainer:case ISurfaceComposerClient::eFXSurfaceBufferState:args.flags | ISurfaceComposerClient::eNoColorFill;[[fallthrough]];case ISurfaceComposerClient::eFXSurfaceEffect: {// 根据args创建Layerresult createBufferStateLayer(args, outResult.handle, layer);std::atomicint32_t* pendingBufferCounter layer-getPendingBufferCounter();if (pendingBufferCounter) {std::string counterName layer-getPendingBufferCounterName();mBufferCountTracker.add(outResult.handle-localBinder(), counterName, pendingBufferCounter);}} break;default:result BAD_VALUE;break;}if (result ! NO_ERROR) {return result;}spLayer parent LayerHandle::getLayer(args.parentHandle.promote());uint32_t outTransformHint;// 将创建好的Layer添加到缓存result addClientLayer(args, outResult.handle, layer, parent, outTransformHint);outResult.layerId layer-sequence;outResult.layerName String16(layer-getDebugName());return result;
}// frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
status_t SurfaceFlinger::createBufferStateLayer(LayerCreationArgs args, spIBinder* handle, spLayer* outLayer) {*outLayer getFactory().createBufferStateLayer(args);*handle (*outLayer)-getHandle();return NO_ERROR;
}// frameworks/native/services/surfaceflinger/SurfaceFlingerDefaultFactory.cpp
spLayer DefaultFactory::createBufferStateLayer(const LayerCreationArgs args) {return spLayer::make(args);
}// frameworks/native/services/surfaceflinger/Layer.cpp
Layer::Layer(const surfaceflinger::LayerCreationArgs args): sequence(args.sequence),mFlinger(spSurfaceFlinger::fromExisting(args.flinger)),mName(base::StringPrintf(%s#%d, args.name.c_str(), sequence)),mClientRef(args.client),mWindowType(static_castWindowInfo::Type(args.metadata.getInt32(gui::METADATA_WINDOW_TYPE, 0))),mLayerCreationFlags(args.flags),mLegacyLayerFE(args.flinger-getFactory().createLayerFE(mName, this)) {// ...
}SurfaceFlinger进程中调用了SurfaceFlinger::createBufferStateLayer方法创建了Layer对象因此SystemServer进程中的SurfaceControl对象对应SurfaceFlinger进程的Layer对象。
上面提到经过App进程到SystemServer进程再到SurfaceFlinger进程最终完成了一系列window相关的对象创建。最终依次返回并将相关信息跨进程拷贝回App进程。之后因为App进程的mSurfaceControl处于有效状态此时将会App进程的mSurface进行更新操作。
public final class ViewRootImpl implements ViewParent, View.AttachInfo.Callbacks, ThreadedRenderer.DrawCallbacks, AttachedSurfaceControl {final W mWindow; // mWindow new W(this);public final Surface mSurface new Surface();private final SurfaceControl mSurfaceControl new SurfaceControl();private boolean mUseBLASTAdapter;private boolean mForceDisableBLAST;// ...public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView, int userId) {synchronized (this) {if (mView null) {mView view;// ...int res;// ...try {// ...res mWindowSession.addToDisplayAsUser(mWindow, mWindowAttributes, getHostVisibility(), mDisplay.getDisplayId(), userId, mInsetsController.getRequestedVisibilities(), inputChannel, mTempInsets, mTempControls);// ...} catch (RemoteException e) {// ...} finally {// ...}// ...// 是否开启BLAST取决于SystemServer进程返回的resif ((res WindowManagerGlobal.ADD_FLAG_USE_BLAST) ! 0) {mUseBLASTAdapter true;}// ...}}}private int relayoutWindow(WindowManager.LayoutParams params, int viewVisibility, boolean insetsPending) throws RemoteException {// ...if (LOCAL_LAYOUT) {// ...} else {relayoutResult mWindowSession.relayout(mWindow, params, requestedWidth, requestedHeight, viewVisibility, insetsPending ? WindowManagerGlobal.RELAYOUT_INSETS_PENDING : 0, mTmpFrames, mPendingMergedConfiguration, mSurfaceControl, mTempInsets, mTempControls, mRelayoutBundle);// ...}// ...// mSurfaceControl实例可用之后根据mSurfaceControl的Surface信息对mSurface进行更新if (mSurfaceControl.isValid()) {if (!useBLAST()) {mSurface.copyFrom(mSurfaceControl);} else {updateBlastSurfaceIfNeeded();}// ...} else {// ...}// ...return relayoutResult;}boolean useBLAST() {return mUseBLASTAdapter !mForceDisableBLAST;}// ...
}在更新mSurface之前会判断是否使用BLAST而是否使用BLAST是在addView的时候由SystemServer进程决定的根据源码可知Android S开始默认开启BLAST因此最后调用了updateBlastSurfaceIfNeeded方法其内部会调用Surface#transferFrom方法进而拷贝mNativeObject的值。
// com.android.server.wm.Session
class Session extends IWindowSession.Stub implements IBinder.DeathRecipient {Overridepublic int addToDisplayAsUser(IWindow window, WindowManager.LayoutParams attrs, int viewVisibility, int displayId, int userId, InsetsType int requestedVisibleTypes, InputChannel outInputChannel, InsetsState outInsetsState, InsetsSourceControl.Array outActiveControls, Rect outAttachedFrame, float[] outSizeCompatScale) {return mService.addWindow(this, window, attrs, viewVisibility, displayId, userId,requestedVisibleTypes, outInputChannel, outInsetsState, outActiveControls,outAttachedFrame, outSizeCompatScale);}
}// com.android.server.wm.WindowManagerService
public class WindowManagerService extends IWindowManager.Stub implements Watchdog.Monitor, WindowManagerPolicy.WindowManagerFuncs {// ...// Whether the system should use BLAST for ViewRootImplfinal boolean mUseBLAST; // Android S之后默认开启// ...private WindowManagerService(Context context, InputManagerService inputManager,boolean showBootMsgs, WindowManagerPolicy policy, ActivityTaskManagerService atm,DisplayWindowSettingsProvider displayWindowSettingsProvider,SupplierSurfaceControl.Transaction transactionFactory,FunctionSurfaceSession, SurfaceControl.Builder surfaceControlFactory) {// ...mUseBLAST Settings.Global.getInt(resolver, Settings.Global.DEVELOPMENT_USE_BLAST_ADAPTER_VR, 1) 1;// ...}public int addWindow(Session session, IWindow client, LayoutParams attrs, int viewVisibility,int displayId, int requestUserId, InsetsType int requestedVisibleTypes,InputChannel outInputChannel, InsetsState outInsetsState,InsetsSourceControl.Array outActiveControls, Rect outAttachedFrame,float[] outSizeCompatScale) {// ...int res mPolicy.checkAddPermission(attrs.type, isRoundedCornerOverlay, attrs.packageName,appOp);if (res ! ADD_OKAY) {return res;}// ...synchronized (mGlobalLock) {// ...res ADD_OKAY;if (mUseBLAST) {res | WindowManagerGlobal.ADD_FLAG_USE_BLAST;}// ...}Binder.restoreCallingIdentity(origId);return res;}public final class ViewRootImpl implements ViewParent, View.AttachInfo.Callbacks, ThreadedRenderer.DrawCallbacks, AttachedSurfaceControl {final W mWindow; // mWindow new W(this);public final Surface mSurface new Surface();private final SurfaceControl mSurfaceControl new SurfaceControl();private BLASTBufferQueue mBlastBufferQueue;private boolean mUseBLASTAdapter;private boolean mForceDisableBLAST;// ...void updateBlastSurfaceIfNeeded() {if (!mSurfaceControl.isValid()) {return;}// 如果对应的native层的SurfaceControl对象是同一个则直接更新即可不需要重新创建BLASTBufferQueueif (mBlastBufferQueue ! null mBlastBufferQueue.isSameSurfaceControl(mSurfaceControl)) {mBlastBufferQueue.update(mSurfaceControl, mSurfaceSize.x, mSurfaceSize.y, mWindowAttributes.format);return;}// 如果更新了SurfaceControl那么销毁并重建BBQBLASTBufferQueue来重置BufferQueue及BLASTBufferQueue的状态.if (mBlastBufferQueue ! null) {mBlastBufferQueue.destroy();}mBlastBufferQueue new BLASTBufferQueue(mTag, mSurfaceControl, mSurfaceSize.x, mSurfaceSize.y, mWindowAttributes.format);mBlastBufferQueue.setTransactionHangCallback(sTransactionHangCallback);Surface blastSurface mBlastBufferQueue.createSurface();// Only call transferFrom if the surface has changed to prevent inc the generation ID and// causing EGL resources to be recreated.mSurface.transferFrom(blastSurface);}// ...
}因此Android S开始由App进程创建管理BufferQueue即ViewRootImpl#mBlastBufferQueue。那BLASTBufferQueue是在什么时候创建的呢查看源码发现其实就是在ViewRootImpl#updateBlastSurfaceIfNeeded方法中创建的。下面看下BLASTBufferQueue的创建过程。
BLASTBufferQueue的创建
根据上面的分析得出App进程在创建完SurfaceControl之后会继续创建BLASTBufferQueue并且在创建BLASTBufferQueue之前并没有发现和图像数据跨进程传输相关的代码实现所以不妨假设下BLASTBufferQueue的创建其实就是为跨进程传输图像数据做准备。
// android.graphics.BLASTBufferQueue
public final class BLASTBufferQueue {// Note: This field is accessed by native code.public long mNativeObject; // BLASTBufferQueue*/** Create a new connection with the surface flinger. */public BLASTBufferQueue(String name, SurfaceControl sc, int width, int height, PixelFormat.Format int format) {this(name, true /* updateDestinationFrame */);update(sc, width, height, format);}public BLASTBufferQueue(String name, boolean updateDestinationFrame) {mNativeObject nativeCreate(name, updateDestinationFrame);}private static native long nativeCreate(String name, boolean updateDestinationFrame);private static native void nativeUpdate(long ptr, long surfaceControl, long width, long height, int format);
}从BLASTBufferQueue的构造函数可以看到和SurfaceControl以及Surface类似都是通过JNI调用到native层去创建对应的对象。因此Java层的BLASTBufferQueue对象也是native层的BLASTBufferQueue的壳因此进一步分析native层的代码。
// frameworks/base/core/jni/android_graphics_BLASTBufferQueue.cpp
static jlong nativeCreate(JNIEnv* env, jclass clazz, jstring jName, jboolean updateDestinationFrame) {ScopedUtfChars name(env, jName);spBLASTBufferQueue queue new BLASTBufferQueue(name.c_str(), updateDestinationFrame);queue-incStrong((void*)nativeCreate);return reinterpret_castjlong(queue.get());
}static void nativeUpdate(JNIEnv* env, jclass clazz, jlong ptr, jlong surfaceControl, jlong width, jlong height, jint format) {spBLASTBufferQueue queue reinterpret_castBLASTBufferQueue*(ptr);queue-update(reinterpret_castSurfaceControl*(surfaceControl), width, height, format);
}native层在创建了BLASTBufferQueue对象之后调用了BLASTBufferQueue::update方法。
// frameworks/native/libs/gui/BLASTBufferQueue.cpp
BLASTBufferQueue::BLASTBufferQueue(const std::string name, bool updateDestinationFrame): mSurfaceControl(nullptr),mSize(1, 1),mRequestedSize(mSize),mFormat(PIXEL_FORMAT_RGBA_8888),mTransactionReadyCallback(nullptr),mSyncTransaction(nullptr),mUpdateDestinationFrame(updateDestinationFrame) {// 1. 先创建BufferQueue然后初始化mProducer以及mConsumercreateBufferQueue(mProducer, mConsumer);// 因为是在client进程因此为dequeue操作设置超时来保证dequeueBuffer时会阻塞线程。mProducer-setDequeueTimeout(std::numeric_limitsint64_t::max());// buffer的默认数量为2mProducer-setMaxDequeuedBufferCount(2);// 封装BufferQueueConsumermBufferItemConsumer new BLASTBufferItemConsumer(mConsumer, GraphicBuffer::USAGE_HW_COMPOSER | GraphicBuffer::USAGE_HW_TEXTURE, 1, false, this);static std::atomicuint32_t nextId 0;mProducerId nextId;mName name # std::to_string(mProducerId);auto consumerName mName (BLAST Consumer) std::to_string(mProducerId);mQueuedBufferTrace QueuedBuffer - mName BLAST# std::to_string(mProducerId);mBufferItemConsumer-setName(String8(consumerName.c_str()));// 2. 设置监听器用于当帧数据可用时消费Buffer数据mBufferItemConsumer-setFrameAvailableListener(this);ComposerServiceAIDL::getComposerService()-getMaxAcquiredBufferCount(mMaxAcquiredBuffers);mBufferItemConsumer-setMaxAcquiredBufferCount(mMaxAcquiredBuffers);mCurrentMaxAcquiredBufferCount mMaxAcquiredBuffers;mNumAcquired 0;mNumFrameAvailable 0;TransactionCompletedListener::getInstance()-addQueueStallListener([](const std::string reason) {std::functionvoid(const std::string) callbackCopy;{std::unique_lock _lock{mMutex};callbackCopy mTransactionHangCallback;}if (callbackCopy) callbackCopy(reason);},this);
}void BLASTBufferQueue::createBufferQueue(spIGraphicBufferProducer* outProducer, spIGraphicBufferConsumer* outConsumer) {spBufferQueueCore core(new BufferQueueCore());// 将BufferQueueCore传入BBQBufferQueueProducer这样当producer发起调用时可以异步化通过持有的BufferQueueCore将结果返回spIGraphicBufferProducer producer(new BBQBufferQueueProducer(core, this));spBufferQueueConsumer consumer(new BufferQueueConsumer(core));consumer-setAllowExtraAcquire(true);*outProducer producer;*outConsumer consumer;
}// frameworks/native/libs/gui/BufferQueueCore.cpp
BufferQueueCore::BufferQueueCore(): mMutex(),mIsAbandoned(false),mConsumerControlledByApp(false), // consumer不是给App控制的mConsumerName(getUniqueName()),mConsumerListener(),mConsumerUsageBits(0),mConsumerIsProtected(false),mConnectedApi(NO_CONNECTED_API),mLinkedToDeath(),mConnectedProducerListener(),mBufferReleasedCbEnabled(false),mBufferAttachedCbEnabled(false),mSlots(), // BufferSlot数组长度为64mQueue(), // 元素类型为BufferItem的Vector变量mFreeSlots(), // 元素类型为int的set对应没有buffer的索引位置mFreeBuffers(), // 元素类型为int的list对应空闲buffer的索引位置mUnusedSlots(), // 元素类型为int的list对应可以被释放的buffer的索引位置mActiveBuffers(), // 元素类型为int的set对应正在使用的buffer的索引位置mDequeueCondition(),mDequeueBufferCannotBlock(false),mQueueBufferCanDrop(false),mLegacyBufferDrop(true),mDefaultBufferFormat(PIXEL_FORMAT_RGBA_8888),mDefaultWidth(1),mDefaultHeight(1),mDefaultBufferDataSpace(HAL_DATASPACE_UNKNOWN),mMaxBufferCount(BufferQueueDefs::NUM_BUFFER_SLOTS),mMaxAcquiredBufferCount(1),mMaxDequeuedBufferCount(1),mBufferHasBeenQueued(false),mFrameCounter(0),mTransformHint(0),mIsAllocating(false),mIsAllocatingCondition(),mAllowAllocation(true),mBufferAge(0),mGenerationNumber(0),mAsyncMode(false),mSharedBufferMode(false),mAutoRefresh(false),mSharedBufferSlot(INVALID_BUFFER_SLOT),mSharedBufferCache(Rect::INVALID_RECT, 0, NATIVE_WINDOW_SCALING_MODE_FREEZE,HAL_DATASPACE_UNKNOWN),mLastQueuedSlot(INVALID_BUFFER_SLOT),mUniqueId(getUniqueId()),mAutoPrerotation(false),mTransformHintInUse(0) {int numStartingBuffers getMaxBufferCountLocked();for (int s 0; s numStartingBuffers; s) {mFreeSlots.insert(s);}for (int s numStartingBuffers; s BufferQueueDefs::NUM_BUFFER_SLOTS;s) {mUnusedSlots.push_front(s);}
}这里创建了BufferQueueCore对象并基于BufferQueueCore对象创建了BBQBufferQueueProducer以及BufferQueueConsumer分别是BufferQueueCore的生产者和消费者并被BLASTBufferQueue的mProducer和mConsumer持有mProducer的主要操作包括dequeueBuffer和queueBuffermConsumer的主要操作包括acquireBuffer和releaseBuffer。
可以看到这里主要是创建了一个BufferQueueCore对象用于管理Buffer而Buffer是通过mProducer和mConsumer使用的所以看下mProducer和mConsumer的内部实现。
BBQBufferQueueProducer的创建
通过源码可以看出mProducer和mConsumer都是通过持有BufferQueueCore来使用buffer的而mProducer和mConsumer中都提供了使用buffer的方法。
// frameworks/native/libs/gui/BLASTBufferQueue.cpp
BBQBufferQueueProducer(const spBufferQueueCore core, wpBLASTBufferQueue bbq) : BufferQueueProducer(core, false /* consumerIsSurfaceFlinger*/), mBLASTBufferQueue(std::move(bbq)) {}BufferQueueConsumer::BufferQueueConsumer(const spBufferQueueCore core) :mCore(core),mSlots(core-mSlots),mConsumerName() {}// frameworks/native/libs/gui/BufferQueueProducer.cpp
BufferQueueProducer::BufferQueueProducer(const spBufferQueueCore core,bool consumerIsSurfaceFlinger) :mCore(core),mSlots(core-mSlots),mConsumerName(),mStickyTransform(0),mConsumerIsSurfaceFlinger(consumerIsSurfaceFlinger),mLastQueueBufferFence(Fence::NO_FENCE),mLastQueuedTransform(0),mCallbackMutex(),mNextCallbackTicket(0),mCurrentCallbackTicket(0),mCallbackCondition(),mDequeueTimeout(-1),mDequeueWaitingForAllocation(false) {}// frameworks/native/libs/gui/include/gui/BufferQueueProducer.h// dequeueBuffer获取下一个buffer的slot索引给producer使用。
// 如果有一个可用的buffer slot那么就把slot索引写入参数处并返回否则返回-EBUSY。
virtual status_t dequeueBuffer(int* outSlot, spFence* outFence, uint32_t width, uint32_t height, PixelFormat format, uint64_t usage, uint64_t* outBufferAge, FrameEventHistoryDelta* outTimestamps) override;// requestBuffer返回GraphicBuffer到第N个slot。
// 通常是在dequeueBuffer第一次slot N的时候。但是如果dequeueBuffer返回的flags表明之前返回的buffers已经失效的话就必须再次调用requestBuffer。
virtual status_t requestBuffer(int slot, spGraphicBuffer* buf);// queueBuffer返回一个填充过的buffer到BufferQueue。
// 调用方必须提供一个fence在所有渲染操作完成之后发送信号。
virtual status_t queueBuffer(int slot, const QueueBufferInput input, QueueBufferOutput* output);// frameworks/native/libs/gui/BufferQueueConsumer.cpp
BufferQueueConsumer::BufferQueueConsumer(const spBufferQueueCore core) :mCore(core),mSlots(core-mSlots),mConsumerName() {}// frameworks/native/libs/gui/include/gui/BufferQueueConsumer.h// acquireBuffer尝试获取BufferQueue中的下一个pending的buffer的使用权如果没有pending的buffer就返回NO_BUFFER_AVAILABLE。 如果一个buffer被成功的获取到将会返回一个包含buffer相关的信息的BufferItem。
virtual status_t acquireBuffer(BufferItem* outBuffer, nsecs_t expectedPresent, uint64_t maxFrameNumber 0) override;// releaseBuffer从消费者处释放一个buffer slot到BufferQueue中。releaseBuffer调用时有可能还在访问buffer的内容。
// 当buffer不再使用的时候fence将会发出信号。
virtual status_t releaseBuffer(int slot, uint64_t frameNumber, const spFence releaseFence, EGLDisplay display, EGLSyncKHR fence);当完成BLASTBufferQueue的创建之后通过update方法更新持有的SurfaceControl变量将其指向新的SurfaceControl对象。
// frameworks/native/libs/gui/BLASTBufferQueue.cpp
void BLASTBufferQueue::update(const spSurfaceControl surface, uint32_t width, uint32_t height, int32_t format) {std::lock_guard _lock{mMutex};if (mFormat ! format) {mFormat format;mBufferItemConsumer-setDefaultBufferFormat(convertBufferFormat(format));}const bool surfaceControlChanged !SurfaceControl::isSameSurface(mSurfaceControl, surface);bool applyTransaction false;// 更新持有的SurfaceControl变量mSurfaceControl surface;SurfaceComposerClient::Transaction t;if (surfaceControlChanged) {t.setFlags(mSurfaceControl, layer_state_t::eEnableBackpressure, layer_state_t::eEnableBackpressure);applyTransaction true;}mTransformHint mSurfaceControl-getTransformHint();mBufferItemConsumer-setTransformHint(mTransformHint);ui::Size newSize(width, height);if (mRequestedSize ! newSize) {mRequestedSize.set(newSize);mBufferItemConsumer-setDefaultBufferSize(mRequestedSize.width, mRequestedSize.height);if (mLastBufferInfo.scalingMode ! NATIVE_WINDOW_SCALING_MODE_FREEZE) {// If the buffer supports scaling, update the frame immediately since the client may// want to scale the existing buffer to the new size.mSize mRequestedSize;if (mUpdateDestinationFrame) {t.setDestinationFrame(mSurfaceControl, Rect(newSize));applyTransaction true;}}}if (applyTransaction) {// All transactions on our apply token are one-way. See comment on mAppliedLastTransactiont.setApplyToken(mApplyToken).apply(false, true);}
}Surface的创建
在创建完BLASTBufferQueue之后会通过新创建的BLASTBufferQueue对象创建一个Surface对象并用新的Surface对象更新ViewRootImpl#mSurface主要是将内部持有的native层的句柄值更新为BLASTBufferQueue对象创建的native的句柄值。
public final class ViewRootImpl implements ViewParent, View.AttachInfo.Callbacks, ThreadedRenderer.DrawCallbacks, AttachedSurfaceControl {final W mWindow; // mWindow new W(this);public final Surface mSurface new Surface();private final SurfaceControl mSurfaceControl new SurfaceControl();private BLASTBufferQueue mBlastBufferQueue;private boolean mUseBLASTAdapter;private boolean mForceDisableBLAST;// ...void updateBlastSurfaceIfNeeded() {if (!mSurfaceControl.isValid()) {return;}// 如果对应的native层的SurfaceControl对象是同一个则直接更新即可不需要重新创建BLASTBufferQueueif (mBlastBufferQueue ! null mBlastBufferQueue.isSameSurfaceControl(mSurfaceControl)) {mBlastBufferQueue.update(mSurfaceControl, mSurfaceSize.x, mSurfaceSize.y, mWindowAttributes.format);return;}// 如果更新了SurfaceControl那么销毁并重建BBQBLASTBufferQueue来重置BufferQueue及BLASTBufferQueue的状态.if (mBlastBufferQueue ! null) {mBlastBufferQueue.destroy();}mBlastBufferQueue new BLASTBufferQueue(mTag, mSurfaceControl, mSurfaceSize.x, mSurfaceSize.y, mWindowAttributes.format);mBlastBufferQueue.setTransactionHangCallback(sTransactionHangCallback);// 通过新创建的BLASTBufferQueue对象创建Surface对象并用新的Surface对象更新mSurfaceSurface blastSurface mBlastBufferQueue.createSurface();// Only call transferFrom if the surface has changed to prevent inc the generation ID and// causing EGL resources to be recreated.mSurface.transferFrom(blastSurface);}// ...
}可以看到最终还是BLASTBufferQueue调用nativeGetSurface到了native层去创建Surface对象这里Surface对象就持有了BLASTBufferQueue的mProducer这样就可以通过Surface访问BBQBufferQueueProducer然后通过BBQBufferQueueProducer访问BufferQueueCore最终实现Buffer的访问使用。
public final class BLASTBufferQueue {/*** return a new Surface instance from the IGraphicsBufferProducer of the adapter.*/public Surface createSurface() {return nativeGetSurface(mNativeObject, false /* includeSurfaceControlHandle */);}private static native Surface nativeGetSurface(long ptr, boolean includeSurfaceControlHandle);
}// frameworks/base/core/jni/android_graphics_BLASTBufferQueue.cpp
static jobject nativeGetSurface(JNIEnv* env, jclass clazz, jlong ptr, jboolean includeSurfaceControlHandle) {spBLASTBufferQueue queue reinterpret_castBLASTBufferQueue*(ptr);return android_view_Surface_createFromSurface(env, queue-getSurface(includeSurfaceControlHandle));
}// frameworks/native/libs/gui/BLASTBufferQueue.cpp
spSurface BLASTBufferQueue::getSurface(bool includeSurfaceControlHandle) {std::lock_guard _lock{mMutex};spIBinder scHandle nullptr;if (includeSurfaceControlHandle mSurfaceControl) {scHandle mSurfaceControl-getHandle();}return new BBQSurface(mProducer, true, scHandle, this);
}// frameworks/native/libs/gui/BLASTBufferQueue.cpp
public:BBQSurface(const spIGraphicBufferProducer igbp, bool controlledByApp, const spIBinder scHandle, const spBLASTBufferQueue bbq) : Surface(igbp, controlledByApp, scHandle), mBbq(bbq) {}// frameworks/native/libs/gui/Surface.cpp
Surface::Surface(const spIGraphicBufferProducer bufferProducer, bool controlledByApp, const spIBinder surfaceControlHandle): mGraphicBufferProducer(bufferProducer),mCrop(Rect::EMPTY_RECT),mBufferAge(0),mGenerationNumber(0),mSharedBufferMode(false),mAutoRefresh(false),mAutoPrerotation(false),mSharedBufferSlot(BufferItem::INVALID_BUFFER_SLOT),mSharedBufferHasBeenQueued(false),mQueriedSupportedTimestamps(false),mFrameTimestampsSupportsPresent(false),mEnableFrameTimestamps(false),mFrameEventHistory(std::make_uniqueProducerFrameEventHistory()) {// Initialize the ANativeWindow function pointers.ANativeWindow::setSwapInterval hook_setSwapInterval;ANativeWindow::dequeueBuffer hook_dequeueBuffer;ANativeWindow::cancelBuffer hook_cancelBuffer;ANativeWindow::queueBuffer hook_queueBuffer;ANativeWindow::query hook_query;ANativeWindow::perform hook_perform;ANativeWindow::dequeueBuffer_DEPRECATED hook_dequeueBuffer_DEPRECATED;ANativeWindow::cancelBuffer_DEPRECATED hook_cancelBuffer_DEPRECATED;ANativeWindow::lockBuffer_DEPRECATED hook_lockBuffer_DEPRECATED;ANativeWindow::queueBuffer_DEPRECATED hook_queueBuffer_DEPRECATED;const_castint(ANativeWindow::minSwapInterval) 0;const_castint(ANativeWindow::maxSwapInterval) 1;// ...
}总结
首先当App进程的View的测量数据发生变化时会导致窗体大小发生变化此时会调用ViewRootImpl#relayoutWindow请求SystemServer进程的WindowManagerService更新窗体的大小SystemServer进程会做如下工作
SystemServer进程通过WindowManagerService创建Java层的SurfaceControl对象对应App进程中Java层的SurfaceControl对象SystemServer进程创建的Java层的SurfaceControl对象是一个壳其内部会通过JNI调用到native层创建native层的SurfaceControl对象并将native层的SurfaceControl对象的句柄值拷贝到App进程的SurfaceControl对象在native层的SurfaceControl对象创建的过程中会通过SurfaceComposerClient请求到SurfaceFlinger进程调用Client::createSurface创建Layer对象并将Layer对象的关键信息返回给 SystemServer进程并用于构造native层的SurfaceControl对象
接着当App进程的Java层的SurfaceControl对象更新了native层的SurfaceControl对象之后便会创建Java层的BLASTBufferQueue对象同样地Java层的BLASTBufferQueue对象会触发native层的BLASTBufferQueue对象的创建native层BLASTBufferQueue对象的创建会做如下工作
创建BufferQueueCore并通过BufferQueueCore创建IGraphicBufferProducerBBQBufferQueueProducer以及BufferQueueConsumer并被BLASTBufferQueue对象持有调用BufferQueueCore#update方法将BufferQueueCore持有的SurfaceControl变量指向之前创建的新SurfaceControl对象
最后当SurfaceControl和BLASTBufferQueue都创建完成之后通过BLASTBufferQueue对象创建一个native层的Surface对象持有了BLASTBufferQueue的IGraphicBufferProducer并将其赋值给App进程的ViewRootImpl#mSurface持有的句柄值最终实现通过Surface访问BBQBufferQueueProducer然后通过BBQBufferQueueProducer访问BufferQueueCore最终对Buffer进行访问使用。
