背景描述
使用QT创建一个视频窗口，使用WEBRTC协议来接收数据并解码，使用SDL2来渲染YUV数据，其中QT进程和SDL所在的渲染进程是跨进程，当SDL使用"software"驱动渲染时，会出现如果窗口大小发生变化，渲染图像的区域没有随窗口改变而改变，这就导致了窗口的部分区域是透明或者是黑的，总太看起来就想是显示异常。

问题分析
通过分析SDL2的源码，发现当窗口进程和渲染进程跨进程时，SDL2内的SetWindowLongPtr函数不能接管窗口的消息过程，导致窗口的所有消息不能被SDL2获取到，从而不能更新显示的区域，也不能适应窗口的变化。

解决办法
渲染YUV数据时获取窗口的大小，当大小发生变化时，重新创建Texture即可，重点看CWebrtcAdapter::createRender函数。

	struct YUVRender {YUVRender(){clear();}void clear(){window = Q_NULLPTR;render = Q_NULLPTR;texture = Q_NULLPTR;view = Q_NULLPTR;yuvWidth = 0;yuvHeight = 0;wndWidth = 0;wndHeight = 0;observeCount = 0;}SDL_Window *window;SDL_Renderer *render;SDL_Texture *texture;void *view;int yuvWidth;int yuvHeight;int wndWidth;int wndHeight;int observeCount;};QMap< int, QPointer<CWebrtcAdapter> > CWebrtcAdapter::s_mapAdapter;
CWebrtcAdapter::CWebrtcAdapter(QObject *parent): QObject(parent), _peerId(INVALID_PEER_ID), _isAudioOnly(false), _ws(Q_NULLPTR), _timer(Q_NULLPTR), _isConnectedYet(false)
{	_funs.fill(nullptr);_contexts.fill(nullptr);connect(this, &CWebrtcAdapter::localSdpRead, this, &CWebrtcAdapter::handleLocalSdp, Qt::QueuedConnection);
}CWebrtcAdapter::~CWebrtcAdapter()
{stop();
}CWebrtcLibrary * CWebrtcAdapter::lib()
{return CWebrtcLibrary::getInstance();
}void CWebrtcAdapter::localSdpReadyToSend(int peer_connection_id, const char* type, const char* sdp)
{GET_ADAPTER(peer_connection_id);emit adapter->localSdpRead(type, sdp);
}void CWebrtcAdapter::start(const QString &stun, bool isRcvOnly)
{qInfo() << "Start, stun:" << stun << " is receive only:" << isRcvOnly;if (!stun.isEmpty()) {QString tmpStun = QString("stun:%1").arg(stun);std::string stun = tmpStun.toStdString();const char* stuns[1] = { stun.c_str() };qInfo() << "Create peer connection, stun:" << stun.c_str();_peerId = lib()->CreatePeerConnection(stuns, 1, "", "", true);} else {_peerId = lib()->CreatePeerConnection(nullptr, 0, "", "", true);}	if (INVALID_PEER_ID == _peerId) {qCritical() << "Create peer connection fail";return;}addToMap(_peerId);lib()->RegisterOnFailure(_peerId, webrtcFailureCallback);lib()->RegisterOnLocalI420FrameReady(_peerId, localI420FrameCallback);lib()->RegisterOnRemoteI420FrameReady(_peerId, remoteI420FrameCallback);lib()->RegisterOnLocalSdpReadytoSend(_peerId, localSdpReadyToSend);lib()->RegisterOnIceCandiateReadytoSend(_peerId, iceCandiateReadyToSend);if (!isRcvOnly) {lib()->AddStream(_peerId, _isAudioOnly);}
}void CWebrtcAdapter::stop()
{sendStopByWebsocket();if (_timer->isActive()) {_timer->stop();}if (INVALID_PEER_ID != _peerId) {lib()->ClosePeerConnection(_peerId);removeFromMap(_peerId);_peerId = INVALID_PEER_ID;}destoryRender(_LocalYuvRender);destoryRender(_remoteYuvRender);clearCallback();_ws->close();
}void CWebrtcAdapter::localI420FrameCallback(int peer_connection_id, const uint8_t* data_y,const uint8_t* data_u,const uint8_t* data_v,const uint8_t* data_a,int stride_y,int stride_u,int stride_v,int stride_a,uint32_t width,uint32_t height)
{
#ifdef TEST_WIRTE_YUV_LOCALFILE *f = fopen("C:\\local.yuv", "ab+");int y_size = stride_y*height;fwrite(data_y, y_size, 1, f);int u_size = stride_u*height / 2;fwrite(data_u, u_size, 1, f);int v_size = stride_v*height / 2;fwrite(data_v, v_size, 1, f);fclose(f);FILE *f1 = fopen("C:\\local.yuv.size", "ab+");QString size = QString("w:%1 h:%2 stride_y:%3 stride_u:%4 stride_v:%5\n").arg(width).arg(height).arg(stride_y).arg(stride_u).arg(stride_v);fwrite(size.toLocal8Bit(), size.toLocal8Bit().size(), 1, f1);fclose(f1);
#endifGET_ADAPTER(peer_connection_id);adapter->createRender(width, height, true);adapter->render(adapter->_LocalYuvRender, data_y, data_u, data_v, stride_y, stride_u, stride_v);
}void CWebrtcAdapter::remoteI420FrameCallback(int peer_connection_id,const uint8_t* data_y, const uint8_t* data_u, const uint8_t* data_v, const uint8_t* data_a, int stride_y, int stride_u, int stride_v, int stride_a, uint32_t width, uint32_t height)
{
#ifdef TEST_WIRTE_YUV_REMOTEFILE *f = fopen("C:\\remote.yuv", "ab+");int y_size = stride_y*height;fwrite(data_y, y_size, 1, f);int u_size = stride_u*height / 2;fwrite(data_u, u_size, 1, f);int v_size = stride_v*height / 2;fwrite(data_v, v_size, 1, f);fclose(f);FILE *f1 = fopen("C:\\remote.yuv.size", "ab+");QString size = QString("w:%1 h:%2 stride_y:%3 stride_u:%4 stride_v:%5\n").arg(width).arg(height).arg(stride_y).arg(stride_u).arg(stride_v);fwrite(size.toLocal8Bit(), size.toLocal8Bit().size(), 1, f1);fclose(f1);
#endifGET_ADAPTER(peer_connection_id);adapter->createRender(width, height, false);adapter->render(adapter->_remoteYuvRender, data_y, data_u, data_v, stride_y, stride_u, stride_v);
}inline void CWebrtcAdapter::createRender(int w, int h, bool isLocal)
{YUVRender &yuvRender = isLocal ? _LocalYuvRender : _remoteYuvRender;bool isResolutionChanged = w != yuvRender.yuvWidth || h != yuvRender.yuvHeight;if (!isResolutionChanged && !determineIsWndSizeChanged(yuvRender) ) {return;}if (Q_NULLPTR == yuvRender.view) {qWarning() << "Create YUV render, view is null";return;}if (w <= 0 || h <= 0) {qWarning() << "Create YUV render, illegal picture width or height";return;}QSize wndSize = getWindowSize(yuvRender.view);if (Q_NULLPTR == yuvRender.window) {yuvRender.window = SDL_CreateWindowFrom(yuvRender.view);qInfo() << "Create a window, size:" << wndSize << "point:" << yuvRender.window << "is local:" << isLocal;if (Q_NULLPTR == yuvRender.window) {qCritical() << "SDL_CreateWindowFrom fail with error description:" << SDL_GetError();return;}} else {if (yuvRender.observeCount > 0) {qInfo() << "Update window size:" << wndSize << "is local:" << isLocal;SDL_SetWindowSize(yuvRender.window, wndSize.width(), wndSize.height());}}if (Q_NULLPTR == yuvRender.render) {yuvRender.render = SDL_CreateRenderer(yuvRender.window, -1, 0);}//Query driver informationSDL_RendererInfo renderer;if (0 == SDL_GetRendererInfo(yuvRender.render, &renderer)) {const char* currentDriver = SDL_GetCurrentVideoDriver();qInfo() << "SDL, driver:" << (Q_NULLPTR != currentDriver ? currentDriver : "unknown") << "renderer:" << renderer.name;//If need observe window size, set variable observeCount larger than zero.yuvRender.observeCount = isDriverNeedObserveWndSize(renderer.name) ? 1 : 0;} else {qWarning() << "SDL, Query driver and renderer failed";}//Attention!//Texture need to destroy first if it is not NULL, because when resolution changed, need recreate itif (Q_NULLPTR != yuvRender.texture) {SDL_DestroyTexture(yuvRender.texture);}	yuvRender.texture = SDL_CreateTexture(yuvRender.render, SDL_PIXELFORMAT_YV12, SDL_TEXTUREACCESS_STREAMING, w, h);yuvRender.yuvWidth = w;yuvRender.yuvHeight = h;yuvRender.wndWidth = wndSize.width();yuvRender.wndHeight = wndSize.height();if (Q_NULLPTR != _funs.at(RegResolution) && isResolutionChanged) {qInfo() << "Resolution notify, width:" << w << "height:" << h << "is local:" << isLocal;reinterpret_cast<resolutionCallback>(_funs.at(RegResolution))(w, h, isLocal, _contexts.at(RegResolution));}
}inline void CWebrtcAdapter::render(YUVRender &render,const uint8_t* data_y, const uint8_t* data_u, const uint8_t* data_v,int stride_y, int stride_u, int stride_v)
{if (Q_NULLPTR == render.texture || Q_NULLPTR == render.render) {qWarning() << "Render, texture or render is null";return;}SDL_UpdateYUVTexture(render.texture, Q_NULLPTR, data_y, stride_y, data_u, stride_u, data_v, stride_v);SDL_RenderCopy(render.render, render.texture, Q_NULLPTR, Q_NULLPTR);SDL_RenderPresent(render.render);
}void CWebrtcAdapter::destoryRender(YUVRender &render)
{if (nullptr != render.texture) {SDL_DestroyTexture(render.texture);}if (nullptr != render.render) {SDL_DestroyRenderer(render.render);}if (Q_NULLPTR != render.window) {SDL_DestroyWindow(render.window);}render.clear();
}void CWebrtcAdapter::setLocalView(void *view)
{_LocalYuvRender.view = view;
}void CWebrtcAdapter::setRemoteView(void *view)
{_remoteYuvRender.view = view;
}void CWebrtcAdapter::addToMap(int peer_id)
{s_mapAdapter.insert(peer_id, QPointer<CWebrtcAdapter>(this));
}void CWebrtcAdapter::removeFromMap(int peer_id)
{s_mapAdapter.remove(peer_id);
}void CWebrtcAdapter::sendStopByWebsocket()
{if (_startCmd.isEmpty()) {return;}QJsonObject obj = QJsonDocument::fromJson(_startCmd.toUtf8()).object();if (!obj.isEmpty()) {obj[KEY(RequestType)] = "stop";sendToWsServer(toJson(obj));}_startCmd.clear();
}void CWebrtcAdapter::registerCallback(RegisterType type, void* fun, void *context)
{_funs[type] = fun;_contexts[type] = context;
}inline void CWebrtcAdapter::clearCallback()
{_funs.fill(nullptr);
}bool CWebrtcAdapter::hasNormallyStopped() const
{return INVALID_PEER_ID == _peerId;
}inline bool CWebrtcAdapter::isDriverNeedObserveWndSize(const QString &driverName) const
{return 0 == driverName.compare("software", Qt::CaseInsensitive);
}bool CWebrtcAdapter::determineIsWndSizeChanged(YUVRender &yuvRender)
{//If driver is "software", need observe windows size//Otherwise, picture will display without fill the windowbool isWndSizeChanged = false;if (yuvRender.observeCount > 0 && Q_NULLPTR != yuvRender.view) {++yuvRender.observeCount;if (yuvRender.observeCount > WND_SIZE_OBSERVER_SPAN) {yuvRender.observeCount = 1;isWndSizeChanged = !isWndSizeEqual(yuvRender);}}return isWndSizeChanged;
}inline QSize CWebrtcAdapter::getWindowSize(void *view) const
{
#ifdef WIN32RECT rect;::GetWindowRect((HWND)view, &rect);return QSize{ rect.right - rect.left + 1, rect.bottom - rect.top + 1 };
#elsereturn QSize();
#endif
}inline bool CWebrtcAdapter::isWndSizeEqual(const YUVRender &yuvRencer) const
{return getWindowSize(yuvRencer.view) == QSize(yuvRencer.wndWidth, yuvRencer.wndHeight);
}