Hi Nuno, another link doing magic with FBO and offscreen rendering, from which I learned a lot: github.com/machinekoder/qml-oled-renderer
God speed, Frank On 07.07.21 08:13, Nuno Santos wrote: > Frank, > > Thanks for your reply. > > I’ve been on your StackOverflow question before! :) Several times actually! > > In the mean time I have found the answer for my question. The trick is to use > QCoreApplication::setAttribute(Qt::AA_ShareOpenGLContexts) before starting > QGuiApplication. > > Then, when initialising the QOpenGLContext that will be used offscreen > renderer, we need to set > _context->setShareContext(QOpenGLContext::globalShareContext()); This way, > the texture is know to both renderers. > > While it is working pretty good on Mac, on Windows I’m having flickering. My > theory is that the texture is being updated while it is being painted. I > might need to find the right time to render the offscreen surface. Maybe > before “beforeRendering” of the main window so that when it paints, the > texture is available. If someone has a solution for this please let me know. > > I’ve also tried another suggestion which is use ShaderEffectSource with the > item I want to capture as source, take it to the C++ level and access to the > textureProvider()->texture() at the afterRendering signal of the main window. > I was not successful with this technic. All I could see was black or rubbish. > This technic would spare me a separate render engine though. > > I know this is not a feature that every single Qt app developer will require > but having official hook for this kind of things would be great. > > I’m using the single threaded version of the rendercontrol example. Since > it's being instantiated and driven by the main thread, it stresses the > process main cpu usage a bit. I will eventually give a try to the multi > threaded version to see if it has more benefits than problems. > > Best regards, > > Nuno > >> On 7 Jul 2021, at 02:36, Frank Mertens <fr...@cyblogic.de >> <mailto:fr...@cyblogic.de>> wrote: >> >> Hey Nuno, >> >> done a lot of QQuickRenderControl tricks lately. But I'm using it on >> QSGRendererInterface::Software. >> I'm not sure if it helps, but check out: >> https://stackoverflow.com/questions/17146747/capture-qml-drawing-buffer-without-displaying/67187802#67187802 >> >> God speed, >> Frank >> >> On 29.06.21 17:27, Nuno Santos wrote: >>> Hi, >>> >>> I’m trying to make a offscreen renderer for a quick scene and then display >>> it’s output in the main and visible QQuickWindow scene. >>> >>> The reason I’m trying to achieve this is because I need to intercept the >>> frames to be able to send them to other programs or encode as a video file. >>> >>> I’ve based myself on the rendercontrol example and I have a working >>> offscreen renderer. Now, what I’m trying to do is to paint the result of >>> the offscreen renderer into the main QQuickWindow. >>> >>> What I’m doing is creating a new QQuickItem that paints a texture. When I >>> declare this item in qml, I register it on the render control. Render >>> control has it’s own render timing. Whenever render control paints, I tell >>> the registered quick item to paint with the fbo texture. >>> >>> The problem is that the only thing that is painted is black. I’m pretty >>> sure the quick item is paint texture correctly because it works with images: >>> >>> // render method >>> >>> … >>> >>> if(_renderView) >>> { >>> _renderView->setImage(_fbo->toImage()); // this works >>> _renderView->setTexture(_quickWindow->createTextureFromId(_fbo->texture(),_size)); >>> // this doesn’t work - only black is painted >>> } >>> >>> … >>> >>> I wonder if I’m stumbling on synchronisation issues. Maybe when its time >>> for the main window to paint again, that texture is not valid anymore. >>> >>> Performance is a key factor in this architecture. I need the fastest >>> solution possible and it doesn’t seem that creating a QImage from a texture >>> and then convert it to QSGTexture is the most performant solution possible. >>> >>> Has anyone been here before? >>> >>> Any advise on how to overcome this problem? >>> >>> Thanks! >>> >>> Best regards, >>> >>> Nuno >>> >>> _______________________________________________ >>> Interest mailing list >>> Interest@qt-project.org >>> https://lists.qt-project.org/listinfo/interest >> >> _______________________________________________ >> Interest mailing list >> Interest@qt-project.org <mailto:Interest@qt-project.org> >> https://lists.qt-project.org/listinfo/interest >
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