Android窗口Surface简介

创建流程

应用程序窗口对应一个Surface（Surface.java）
Surface由每个应用进程的ViewRootImpl持有
Surface最初初始化为一个空Surface
Surface的初始化发生在第一次relayoutWindow

css 复制代码

[View.invalidate]  
    ↓  
[逐级传递到 ViewRootImpl]  
    ↓  
[ViewRootImpl.scheduleTraversals()]  
    ↓  
[插入同步屏障，注册 VSYNC 回调]  
    ↓  
[VSYNC 信号到达 → 执行 doTraversal() → performTraversals() → relayoutWindow]
    ↓
[执行updateBlastSurfaceIfNeeded()]
    ↓
[创建BLASTBufferQueue → mBlastBufferQueue.createSurface() → mSurface.transferFrom(blastSurface)]

接下来分析Java层BLASTBufferQueue的createSurface创建流程

BLASTBufferQueue.createSurface

Java层的createSurface对应到jni中的nativeGetSurface
jni层中，通过BLASTBufferQueue::getSurface获取Surface
在BLASTBufferQueue::getSurface中创建并返回了一个BBQSurface

c++ 复制代码

sp<Surface> BLASTBufferQueue::getSurface(bool includeSurfaceControlHandle) {
    std::lock_guard _lock{mMutex};
    sp<IBinder> scHandle = nullptr;
    if (includeSurfaceControlHandle && mSurfaceControl) {
        scHandle = mSurfaceControl->getHandle();
    }
    return new BBQSurface(mProducer, true, scHandle, this);
}

BBQSurface关联了BBQ中的生产者、SurfaceControl、还有BBQ自己本身
Java层窗口对应的Surface在native层包装的是BBQSurface

将Surface设置给hwui

接着上一节，在performTraversals()中创建Surface后，接着会进行更新Surface

c++ 复制代码

private void performTraversals() {
    ...
    } else if ((surfaceReplaced || surfaceSizeChanged || updateSurfaceNeeded)
                        && mSurfaceHolder == null
                        && mAttachInfo.mThreadedRenderer != null
                        && mSurface.isValid()) {
        mFullRedrawNeeded = true;
        try {
            // Need to do updateSurface (which leads to CanvasContext::setSurface and
            // re-create the EGLSurface) if either the Surface changed (as indicated by
            // generation id), or WindowManager changed the surface size. The latter is
            // because on some chips, changing the consumer side's BufferQueue size may
            // not take effect immediately unless we create a new EGLSurface.
            // Note that frame size change doesn't always imply surface size change (eg.
            // drag resizing uses fullscreen surface), need to check surfaceSizeChanged
            // flag from WindowManager.
            mAttachInfo.mThreadedRenderer.updateSurface(mSurface);
        } catch (OutOfResourcesException e) {
            handleOutOfResourcesException(e);
            mLastPerformTraversalsSkipDrawReason = "oom_update_surface";
            return;
        }
    }
}

从java层一层层调用到SkiaPipeline
需要注意的一点是在jni层，会将Surface转成ANativeWindow，在hwui模块中只能感知到ANativeWindow的存在
在skiapipeline中根据opengl、vulkan后端，区分不同的流程（Android15中已经默认走vulkan）
- （opengl），在SkiaOpenGLPipeline中调用setSurface，然后是EglManager.createSurace将ANativeWindow转成EGLSurface

渲染

还有一条非常隐蔽的线，在SkiaPipeline renderFrame渲染每帧内容时，用的是SkSurface，SkSurface与EGLSurface的关联是源码中看不到的
在SkiaPipeline中通过MakeFromBackendRenderTarget创建SkSurface时，需要传入GrBackendRenderTarget（封装了 EGLSurface 的帧缓冲区对象 FBO）