Render into a QQuikItem

I know this is an old post, but I have the same problem in 2020. I have tried lots of examples from github and other sources. My QQuickFramebufferObject has two problems:

1. it renders on complete window

2. It is flickering on resize.

This is the code:

        //================================================================
        // Item
        //================================================================
        
        OcctViewItem::OcctViewItem(QQuickItem *parent) : QQuickFramebufferObject(parent)
        {
            setMirrorVertically(true);
        }

        OcctViewItem::~OcctViewItem() {
        }
        
        QQuickFramebufferObject::Renderer * OcctViewItem::createRenderer() const
        {
            return new OcctFboRenderer();
        }
        
        //================================================================
        // Renderer
        //================================================================

        OcctFboRenderer::OcctFboRenderer() { 
        }

        OcctFboRenderer::~OcctFboRenderer()
        {
            context_.Nullify();
            view_.Nullify();
            viewer_.Nullify();
            window_ = nullptr;
        }

        void OcctFboRenderer::render()
        {
            QOpenGLContext::currentContext()->functions()->glUseProgram(0);
            if (!view_.IsNull()) {
                view_->Redraw();
                view_->MustBeResized();               
            }
            window_->resetOpenGLState();
        }

        QOpenGLFramebufferObject * OcctFboRenderer::createFramebufferObject(const QSize &size)
        {
            QOpenGLFramebufferObjectFormat format;
            //format.setSamples(4);
            format.setAttachment(QOpenGLFramebufferObject::CombinedDepthStencil);
            return new QOpenGLFramebufferObject(size, format);
        }

        void OcctFboRenderer::synchronize(QQuickFramebufferObject * item)
        {
            if (!window_) {
                window_ = item->window();
                window_->setClearBeforeRendering(Standard_False);
            }
            OcctViewItem * self = static_cast<OcctViewItem*> (item);

            // If the viewer is not yet initialized, initialize it.
            if (viewer_.IsNull()) {
                this->initializeViewer(Aspect_Drawable(window_->winId()), self);
            }

            // Get the control position and size.
            QPoint viewportPos = self->mapToGlobal(QPointF(0, 0)).toPoint();
            QSize viewportSize = self->size().toSize();

            // Check if the viewPort needs to be resized.
            if (viewportPos.x() != viewportPos_.x() || viewportPos.y() != viewportPos_.y()) {
                view_->MustBeResized();
            }
            if (viewportSize.width() != viewportSize_.width() || viewportSize.height() != viewportSize_.height()) {
                view_->MustBeResized();
                view_->Invalidate();
            }

            // Store the current pos and size.
            viewportPos_ = viewportPos;
            viewportSize_ = viewportSize;

        }

        void OcctFboRenderer::initializeViewer(const Aspect_Drawable& drawable, OcctViewItem * occView)
        {
            Q_ASSERT(viewer_.IsNull());

            // Request device and render context.
            auto renderContext = window_->openglContext();
            if (drawable == 0 || renderContext == 0)
                return;

            // Setup display driver.
            Handle(Aspect_DisplayConnection) display = new Aspect_DisplayConnection();
            Handle(OpenGl_GraphicDriver) driver = new OpenGl_GraphicDriver(display, Standard_False);

            // Create and setup the viewer.
            viewer_ = new V3d_Viewer(driver);
            viewer_->SetDefaultBackgroundColor(Quantity_NOC_GRAY50);
            viewer_->SetDefaultLights();
            viewer_->SetLightOn();

            // Create and setup interactivity context.
            context_ = new AIS_InteractiveContext(viewer_);
            context_->SetDisplayMode(AIS_Shaded, Standard_True);

            // Create and setup window.
            Handle(OcctWindow) occtWnd = new OcctWindow(window_);
            if (!occtWnd->IsMapped()) {
                occtWnd->Map();
            }

            // Create and setup view.
            view_ = viewer_->CreateView();
            view_->ChangeRenderingParams().NbMsaaSamples = 4;
            view_->ChangeRenderingParams().IsAntialiasingEnabled = Standard_True;
            view_->SetImmediateUpdate(Standard_False);
            //view_->SetWindow(occtWnd, reinterpret_cast<Aspect_RenderingContext>(renderContext));
            view_->SetWindow(occtWnd);
            
            
            view_->TriedronDisplay(Aspect_TOTP_RIGHT_LOWER, Quantity_NOC_WHITESMOKE, 0.1, V3d_ZBUFFER);

            // Create a demo scene.
            this->initScene();

        }

               
        void OcctFboRenderer::initScene()
        {
            // Create a bisque cone at [0, 10, 0].
            gp_Ax2 axis;
            axis.SetLocation(gp_Pnt(0.0, 10.0, 0.0));

            TopoDS_Shape bisqueCone = BRepPrimAPI_MakeCone(axis, 3.0, 1.5, 5.0).Shape();
            Handle(AIS_Shape) bisqueConeShape = new AIS_Shape(bisqueCone);
            bisqueConeShape->SetColor(Quantity_NOC_BISQUE);

            // Create a chocolate cone at [8, 10, 0].
            axis.SetLocation(gp_Pnt(8.0, 10.0, 0.0));
            TopoDS_Shape chocoCone = BRepPrimAPI_MakeCone(axis, 3.0, 0.0, 5.0).Shape();
            Handle(AIS_Shape) chocoConeShape = new AIS_Shape(chocoCone);
            chocoConeShape->SetColor(Quantity_NOC_CHOCOLATE);

            context_->Display(bisqueConeShape, Standard_True);
            context_->Display(chocoConeShape, Standard_True);

            // Fit all into the view.
            view_->FitAll();


        }

- First render is black screen: screenshot.png

https://www.opencascade.com/system/files/forum/screenshot.png

- While resizing, flick between screenshot_1.png and screenshot_2.png

https://www.opencascade.com/system/files/forum/screenshot_1.png

https://www.opencascade.com/system/files/forum/screenshot_2.png

Thank you for your help,

Frank.

Thank you Kirill,

I already solved the problem, I was experimenting with QQuickFramebufferObject and didn't understand it very well at first. After I Implemented an Aspect_Window and separate rendering code from the GUI thread, everything started to work very well.

Cheers!