View绘制上屏流程

原创已于 2025-02-04 21:31:58 修改 · 1.2k 阅读

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于 2024-12-12 16:51:15 首次发布

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App显示在屏幕上完整流程：

android12开始，producer，consumer，BufferQueue以及Buffer的dequeue，queue，acquire，release都从SurfaceFlinger移到了App端实现，如下图

View上屏流程：

view.invalidate/requestlayout发出绘制请求
vsync会触发绘制请求任务（uithread调用syncframestate把界面元素传递给RenderThread生成displaylist）
RenderThread调用opengl接口把displaylist绘制成像素放到graphicbuffer，然后再调用queuebuffer放到App的bufferqueue（release fence）

App queueBuffer→ frameAvailableListener.onFrameAvailable→BufferQueueConsumer::processNextBufferLocked

binder通知SurfaceFlinger.BufferQueueConsumer::acquireBuffer 获取一个graphicbuffer调用SurfaceComposerClient::Transaction.setBuffer保存到surfaceflinger layer中，并向hwc发送vsync请求

SurfaceFlinger在下一个vsync到来后询问hwc每个layer是否需要gpu合成

gpu合成：renderengine模块把所有window的bufferqueue调用aquirebuffer拿到要合成buffer，调用gpu合成之后放到framebuffer，hwc再根据framebuffer合成1个layer走device合成过程，并释放fence（ gpu合成原理是通过拿到可用buffer合成帧数据放到framebufferlayers合成_surfaceflinger 合成是通过hwc还是gpu-优快云博客）
device合成：layer直接透传到hwc，透传给display，display从每个layer的bufferqueue中读取像素显示到屏幕

SurfaceFlinger消费bufferqueque

onVsync -> SurfaceFlinger::onMessageInvalidate() -> BufferLayer::latchBuffer() -> BufferQueueLayer::updateTexImage()

{

BufferLayerConsumer::acquireBufferLocked()
BufferLayerConsumer::updateAndReleaseLocked

}

Surfaceflinger RenderEngine负责把每个texture合成生成framebuffer之后交给hwc消费

SkiaGLRenderEngine.cpp文件在native/libs/renderengine 目录下
drawlayers方法负责将所有layers的buffer描画到屏幕的framebuffer中，drawlayers方法在描画中，会根据layerSettings的具体信息为各个layer添加某些显示特效（例如圆角窗口，窗口阴影，高斯模糊效果）

多个App在屏幕上显示流程：

1个App Window从SurfaceFlinger申请1个surface时，会创建1个window对应的BufferQueue，每个BufferQueue包含3个buffer（SF合成图像也是在Gpu完成的）

关键流程

一，App完成1帧数据时把生产的buffer通过binder传给SurfaceFlinger去消费

queueBuffer→frameAvailableListener.onFrameAvailable

→BufferQueueConsumer::processNextBufferLocked→BufferQueueConsumer::acquireBuffer

（像app要buffer来消费）

→BLASTBufferQueue#SurfaceComposerClient::Transaction.setBuffer(mSurfaceControl, buffer, releaseCallbackId, releaseBufferCallback)

二，SurfaceFlinger消费完之后releasebuffer

Surfaceflinger E TransactionCallbackInvoker: TransactionCallbackInvoker ITransactionCompletedListener onTransactionCompleted
Surfaceflinger E ITransactionCompletedListener:onTransact BpTransactionCompletedListener onTransactionCompleted
Client ITransactionCompletedListener: -----------------------onTransact BnTransactionCompletedListener onTransactionCompleted
Client BLASTBufferQueue: releaseBufferCallbackThunk→ProducerListener.onBufferReleased()
Client BufferQueueConsumer: [SurfaceView[com.jidu.rearscreen/com.jidu.rearscreen.MainActivity]#1(BLAST Consumer)1]
Client releaseBuffer: releasing slot 0

调用stack如下

BufferQueueConsumer: stackdump:#00 pc 000580ff  /system/lib/libgui.so (android::BufferQueueConsumer::releaseBuffer(int, unsigned long long, android::sp<android::Fence> const&, void*, void*)+130)
BufferQueueConsumer: stackdump:#01 pc 00059117  /system/lib/libgui.so (android::BufferQueueConsumer::releaseBuffer(int, unsigned long long, void*, void*, android::sp<android::Fence> const&)+30)
BufferQueueConsumer: stackdump:#02 pc 00076d27  /system/lib/libgui.so (android::ConsumerBase::releaseBufferLocked(int, android::sp<android::GraphicBuffer>, void*, void*)+134)
BufferQueueConsumer: stackdump:#03 pc 0007580d  /system/lib/libgui.so (android::BufferItemConsumer::releaseBuffer(android::BufferItem const&, android::sp<android::Fence> const&)+140)
BufferQueueConsumer: stackdump:#04 pc 0006c467  /system/lib/libgui.so (android::BLASTBufferQueue::releaseBufferCallback(android::ReleaseCallbackId const&, android::sp<android::Fence> const&, unsigned int, unsigned int)+1362)
BufferQueueConsumer: stackdump:#05 pc 0006d827  /system/lib/libgui.so (android::releaseBufferCallbackThunk(android::wp<android::BLASTBufferQueue>, android::ReleaseCallbackId const&, android::sp<android::Fence> const&, unsigned int, unsigned int)+62)
BufferQueueConsumer: stackdump:#06 pc 0007039b  /system/lib/libgui.so (std::__1::__function::__func<std::__1::__bind<void (&)(android::wp<android::BLASTBufferQueue>, android::ReleaseCallbackId const&, android::sp<android::Fence> const&, unsigned int, unsigned int), android::wp<android::BLASTBufferQueue>, std::__1::placeholders::__ph<1> const&, std::__1::placeholders::__ph<2> const&, std::__1::placeholders::__ph<3> const&, std::__1::placeholders::__ph<4> const&>, std::__1::allocator<std::__1::__bind<void (&)(android::wp<android::BLASTBufferQueue>, android::ReleaseCallbackId const&, android::sp<android::Fence> const&, unsigned int, unsigned int), android::wp<android::BLASTBufferQueue>, std::__1::placeholders::__ph<1> const&, std::__1::placeholders::__ph<2> const&, std::__1::placeholders::__ph<3> const&, std::__1::placeholders::__ph<4> const&> >, void (android::ReleaseCallbackId const&, android::sp<android::Fence> const&, unsigned int, unsigned int)>::operator()(android::ReleaseCallbackId const&, android::sp<android::Fence> const&,
BufferQueueConsumer: stackdump:#07 pc 000a7d47  /system/lib/libgui.so (android::TransactionCompletedListener::onTransactionCompleted(android::ListenerStats)+3382)
BufferQueueConsumer: stackdump:#08 pc 000925a5  /system/lib/libgui.so (int android::SafeBnInterface<android::ITransactionCompletedListener>::callLocalAsync<void (android::ITransactionCompletedListener::*)(android::ListenerStats)>(android::Parcel const&, android::Parcel*, void (android::ITransactionCompletedListener::*)(android::ListenerStats))+204)
BufferQueueConsumer: stackdump:#09 pc 00028ddb  /system/lib/libbinder.so (android::BBinder::transact(unsigned int, android::Parcel const&, android::Parcel*, unsigned int)+162)

12-15 10:46:54.793667  2959  3319 E BufferQueueProducer: [SurfaceView[com.jidu.renderframe/com.jidu.renderframe.MainActivity]#1(BLAST Consumer)1](id:b8f00000001,api:1,p:2959,c:2959) queueBuffer: slot=0/19261 time=652049692092 dataSpace=0 validHdrMetadataTypes=0x0 crop=[0,0,0,0] transform=0 scale=SCALE_TO_WINDOW
12-15 10:46:54.793705  2959  3319 E BufferQueueConsumer: [SurfaceView[com.jidu.renderframe/com.jidu.renderframe.MainActivity]#1(BLAST Consumer)1](id:b8f00000001,api:1,p:2959,c:2959) acquireBuffer: acquiring { slot=0/19261 buffer=0x74f1a1b440 } notify_all  queuesize:1

12-15 10:46:54.802876  2959  3319 E BufferQueueProducer: [SurfaceView[com.jidu.renderframe/com.jidu.renderframe.MainActivity]#1(BLAST Consumer)1](id:b8f00000001,api:1,p:2959,c:2959) dequeueBuffer

12-15 10:46:54.742224  2959  3028 E BufferQueueConsumer: [SurfaceView[com.jidu.renderframe/com.jidu.renderframe.MainActivity]#1(BLAST Consumer)1](id:b8f00000001,api:1,p:2959,c:2959) releaseBuffer: releasing slot 2 DequeueCondition.notify_all
源码如下：
    void onReleaseBuffer(ReleaseCallbackId callbackId, sp<Fence> releaseFence,
                         uint32_t transformHint, uint32_t currentMaxAcquiredBufferCount) override {
                         
        callRemoteAsync<decltype(
                &ITransactionCompletedListener::onReleaseBuffer)>(Tag::ON_RELEASE_BUFFER,
                                                                  callbackId, releaseFence,
                                                                  transformHint,
                                                                currentMaxAcquiredBufferCount);
}

releaseBuffer流程：

BufferStateLayer::~BufferStateLayer onReleaseBuffer
12-25 21:00:18.606   603   603 E ITransactionCompletedListener: -----------------------onTransact BpTransactionCompletedListener onTransactionCompleted
12-25 21:00:18.606 12674 14754 E ITransactionCompletedListener: -----------------------onTransact BnTransactionCompletedListener onTransactionCompleted
12-25 21:00:18.606 12674 14754 E BLASTBufferQueue: releaseBufferCallbackThunk    BufferQueueConsumer:releaseBuffer: releasing slot x

Systrace全流程：

App绘制到dequeue到buffer
Consumer aquirebuffer之后把buffer设置给Surfaceflinger
Surfaceflinger 消费完了 releaseBuffer

关键概念：

sf合成layer方式：优先硬件合成，合成失败才用gpu合成兜底

1种：hwc（高通开发的屏幕芯片dpu做）硬件合成，但是不能合成alpha,高斯模糊这种复杂图像

1种：soft （client/gpu）不会出错, cpu占用高

SurfaceFlinger的线程：acquire,queue,dequeue采用主线程，releaseBuffer采用子线程
BBQ（BufferQueue的增强类BlastBufferQueue）【BufferQueue中是BufferSlot来保存Buffer状态，1个Buffer有四种状态: Dequeued, Queued, Acquired, Free】
QueuedBuffer - X 生产者队列，sf会从这个队列中获取buffer
BLAST Consumer - X 消费者队列
SurfaceFlinger为每个surface创建的BufferStateLayer，封装在mSurfaceControl暴露给客户端，mSurfaceControl中新建了BLASTBufferQueue
BLASTBufferQueue分别又创建BufferQueueCore，BufferQueueProducer，BufferQueueConsumer持有相同的BufferQueueCore：
BufferQueueCore是graphicbuffer存储的数据结构，包含如下2个变量：

mSlots：包含了默认大小为64的BufferSlot数组,但一个surface默认初始化3个buffrer，

mQueue ：BufferItem类型的数组，生产者和消费者按照Fifo规则消费queque中的数据

Producer调用queueBuffer后会修改mSlots，mQueue（但不知道这2个的区别在哪里）

BufferSlot是1个graphicbuffer封装，成员变量有mGraphicBuffer，mBufferState（buffer的状态是free，queued,aquired,dequeue）, mFence(前主人是否用完的标志),SurfaceTexture可以对Graphic Buffers做自定义特效处理
将图形内存Graphic Buffer送到LCD显示的2种方法：gpu合成gralloc.post()和hwcomposer的硬件合成
从view.invalide()提交绘制请求到display显示至少隔3帧(一个surface和SurfaceFlinger有3个buffer轮流使用)
dequeueBuffer阻塞之后有timeout(默认是4s） W OpenGLRenderer: dequeueBuffer failed, error = -110; switching to fallback
关于dequeueBuffer等buffer相关bug，搜索：SurfaceFlinger，dequeueBuffer关键字
fence机制：fence对象通过fd在3个进程之间共享
释放fence时机：App在gpu绘制一帧完毕，SurfaceFlinger在updateTexImage，HWC在合成完毕（HWC合成开始前提是gpu和device合成用到的fence都可用）
错误汇总：

04-20 15:05:56.217276 597 597 E SurfaceFlinger: Attempted to create an ExternalTexture for layer lrc#0 that exceeds render target size limit.
12-14 15:55:53.495030 583 583 E BpTransactionCompletedListener: Failed to transact (-2147483646) surfaceflinger通知释放buffer失败了
RenderThread: BufferQueueProducer: setDequeueTimeout:4000（

但注意！UnityMain Thread:一直阻塞不会Timeout,BufferQueueProducer: [SurfaceView[com.cottongame.triangleAdventure.jidu/com.unity3d.player.MainActivity]#1(BLAST Consumer)1]
trace分析卡顿，Davey! duration主线程卡顿