window_singlethreaded.cpp Example File | Qt Quick 5.12.11

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- QQuickRenderControl Example
- window_singlethreaded.cpp Example File
- Qt 5.12.11 Reference Documentation

# window_singlethreaded.cpp Example File

rendercontrol/window_singlethreaded.cpp

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     #include "window_singlethreaded.h"
     #include "cuberenderer.h"
     #include <QOpenGLContext>
     #include <QOpenGLFunctions>
     #include <QOpenGLFramebufferObject>
     #include <QOpenGLShaderProgram>
     #include <QOpenGLVertexArrayObject>
     #include <QOpenGLBuffer>
     #include <QOpenGLVertexArrayObject>
     #include <QOffscreenSurface>
     #include <QScreen>
     #include <QQmlEngine>
     #include <QQmlComponent>
     #include <QQuickItem>
     #include <QQuickWindow>
     #include <QQuickRenderControl>
     #include <QCoreApplication>

     class RenderControl : public QQuickRenderControl
     {
     public:
         RenderControl(QWindow *w) : m_window(w) { }
         QWindow *renderWindow(QPoint *offset) override;

     private:
         QWindow *m_window;
     };

     QWindow *RenderControl::renderWindow(QPoint *offset)
     {
         if (offset)
             *offset = QPoint(0, 0);
         return m_window;
     }

     WindowSingleThreaded::WindowSingleThreaded()
         : m_rootItem(nullptr),
           m_fbo(nullptr),
           m_quickInitialized(false),
           m_quickReady(false),
           m_dpr(0)
     {
         setSurfaceType(QSurface::OpenGLSurface);

         // The rendercontrol does not necessarily need an FBO. Demonstrate this
         // when requested.
         m_onscreen = QCoreApplication::arguments().contains(QStringLiteral("--onscreen"));

         QSurfaceFormat format;
         // Qt Quick may need a depth and stencil buffer. Always make sure these are available.
         format.setDepthBufferSize(16);
         format.setStencilBufferSize(8);
         setFormat(format);

         m_context = new QOpenGLContext;
         m_context->setFormat(format);
         m_context->create();

         m_offscreenSurface = new QOffscreenSurface;
         // Pass m_context->format(), not format. Format does not specify and color buffer
         // sizes, while the context, that has just been created, reports a format that has
         // these values filled in. Pass this to the offscreen surface to make sure it will be
         // compatible with the context's configuration.
         m_offscreenSurface->setFormat(m_context->format());
         m_offscreenSurface->create();

         m_cubeRenderer = new CubeRenderer(m_offscreenSurface);

         m_renderControl = new RenderControl(this);

         // Create a QQuickWindow that is associated with out render control. Note that this
         // window never gets created or shown, meaning that it will never get an underlying
         // native (platform) window.
         m_quickWindow = new QQuickWindow(m_renderControl);

         // Create a QML engine.
         m_qmlEngine = new QQmlEngine;
         if (!m_qmlEngine->incubationController())
             m_qmlEngine->setIncubationController(m_quickWindow->incubationController());

         // When Quick says there is a need to render, we will not render immediately. Instead,
         // a timer with a small interval is used to get better performance.
         m_updateTimer.setSingleShot(true);
         m_updateTimer.setInterval(5);
         connect(&m_updateTimer, &QTimer::timeout, this, &WindowSingleThreaded::render);

         // Now hook up the signals. For simplicy we don't differentiate between
         // renderRequested (only render is needed, no sync) and sceneChanged (polish and sync
         // is needed too).
         connect(m_quickWindow, &QQuickWindow::sceneGraphInitialized, this, &WindowSingleThreaded::createFbo);
         connect(m_quickWindow, &QQuickWindow::sceneGraphInvalidated, this, &WindowSingleThreaded::destroyFbo);
         connect(m_renderControl, &QQuickRenderControl::renderRequested, this, &WindowSingleThreaded::requestUpdate);
         connect(m_renderControl, &QQuickRenderControl::sceneChanged, this, &WindowSingleThreaded::requestUpdate);

         // Just recreating the FBO on resize is not sufficient, when moving between screens
         // with different devicePixelRatio the QWindow size may remain the same but the FBO
         // dimension is to change regardless.
         connect(this, &QWindow::screenChanged, this, &WindowSingleThreaded::handleScreenChange);
     }

     WindowSingleThreaded::~WindowSingleThreaded()
     {
         // Make sure the context is current while doing cleanup. Note that we use the
         // offscreen surface here because passing 'this' at this point is not safe: the
         // underlying platform window may already be destroyed. To avoid all the trouble, use
         // another surface that is valid for sure.
         m_context->makeCurrent(m_offscreenSurface);

         // Delete the render control first since it will free the scenegraph resources.
         // Destroy the QQuickWindow only afterwards.
         delete m_renderControl;

         delete m_qmlComponent;
         delete m_quickWindow;
         delete m_qmlEngine;
         delete m_fbo;

         m_context->doneCurrent();

         delete m_cubeRenderer;

         delete m_offscreenSurface;
         delete m_context;
     }

     void WindowSingleThreaded::createFbo()
     {
         // The scene graph has been initialized. It is now time to create an FBO and associate
         // it with the QQuickWindow.
         m_dpr = devicePixelRatio();
         if (!m_onscreen) {
             m_fbo = new QOpenGLFramebufferObject(size() * m_dpr, QOpenGLFramebufferObject::CombinedDepthStencil);
             m_quickWindow->setRenderTarget(m_fbo);
         } else {
             // Special case: No FBO. Render directly to the window's default framebuffer.
             m_onscreenSize = size() * m_dpr;
             m_quickWindow->setRenderTarget(0, m_onscreenSize);
         }
     }

     void WindowSingleThreaded::destroyFbo()
     {
         delete m_fbo;
         m_fbo = nullptr;
     }

     void WindowSingleThreaded::render()
     {
         QSurface *surface = m_offscreenSurface;
         if (m_onscreen)
             surface = this;
         if (!m_context->makeCurrent(surface))
             return;

         // Polish, synchronize and render the next frame (into our fbo).  In this example
         // everything happens on the same thread and therefore all three steps are performed
         // in succession from here. In a threaded setup the render() call would happen on a
         // separate thread.
         m_renderControl->polishItems();
         m_renderControl->sync();
         m_renderControl->render();

         m_quickWindow->resetOpenGLState();
         QOpenGLFramebufferObject::bindDefault();

         m_context->functions()->glFlush();

         m_quickReady = true;

         // Get something onto the screen.
         if (!m_onscreen)
             m_cubeRenderer->render(this, m_context, m_quickReady ? m_fbo->texture() : 0);
         else
             m_context->swapBuffers(this);
     }

     void WindowSingleThreaded::requestUpdate()
     {
         if (!m_updateTimer.isActive())
             m_updateTimer.start();
     }

     void WindowSingleThreaded::run()
     {
         disconnect(m_qmlComponent, &QQmlComponent::statusChanged, this, &WindowSingleThreaded::run);

         if (m_qmlComponent->isError()) {
             const QList<QQmlError> errorList = m_qmlComponent->errors();
             for (const QQmlError &error : errorList)
                 qWarning() << error.url() << error.line() << error;
             return;
         }

         QObject *rootObject = m_qmlComponent->create();
         if (m_qmlComponent->isError()) {
             const QList<QQmlError> errorList = m_qmlComponent->errors();
             for (const QQmlError &error : errorList)
                 qWarning() << error.url() << error.line() << error;
             return;
         }

         m_rootItem = qobject_cast<QQuickItem *>(rootObject);
         if (!m_rootItem) {
             qWarning("run: Not a QQuickItem");
             delete rootObject;
             return;
         }

         // The root item is ready. Associate it with the window.
         m_rootItem->setParentItem(m_quickWindow->contentItem());

         // Update item and rendering related geometries.
         updateSizes();

         // Initialize the render control and our OpenGL resources.
         QSurface *surface = m_offscreenSurface;
         if (m_onscreen)
             surface = this;
         m_context->makeCurrent(surface);
         m_renderControl->initialize(m_context);
         m_quickInitialized = true;
     }

     void WindowSingleThreaded::updateSizes()
     {
         // Behave like SizeRootObjectToView.
         m_rootItem->setWidth(width());
         m_rootItem->setHeight(height());

         m_quickWindow->setGeometry(0, 0, width(), height());

         m_cubeRenderer->resize(width(), height());
     }

     void WindowSingleThreaded::startQuick(const QString &filename)
     {
         m_qmlComponent = new QQmlComponent(m_qmlEngine, QUrl(filename));
         if (m_qmlComponent->isLoading())
             connect(m_qmlComponent, &QQmlComponent::statusChanged, this, &WindowSingleThreaded::run);
         else
             run();
     }

     void WindowSingleThreaded::exposeEvent(QExposeEvent *)
     {
         if (isExposed()) {
             if (!m_quickInitialized) {
                 if (!m_onscreen)
                     m_cubeRenderer->render(this, m_context, m_quickReady ? m_fbo->texture() : 0);
                 startQuick(QStringLiteral("qrc:/rendercontrol/demo.qml"));
             }
         }
     }

     void WindowSingleThreaded::resizeFbo()
     {
         QSurface *surface = m_offscreenSurface;
         if (m_onscreen)
             surface = this;
         if (m_rootItem && m_context->makeCurrent(surface)) {
             delete m_fbo;
             createFbo();
             m_context->doneCurrent();
             updateSizes();
             render();
         }
     }

     void WindowSingleThreaded::resizeEvent(QResizeEvent *)
     {
         // If this is a resize after the scene is up and running, recreate the fbo and the
         // Quick item and scene.
         if (!m_onscreen) {
             if (m_fbo && m_fbo->size() != size() * devicePixelRatio())
                 resizeFbo();
         } else {
             if (m_onscreenSize != size() * devicePixelRatio())
                 resizeFbo();
         }
     }

     void WindowSingleThreaded::handleScreenChange()
     {
         if (m_dpr != devicePixelRatio())
             resizeFbo();
     }

     void WindowSingleThreaded::mousePressEvent(QMouseEvent *e)
     {
         // Use the constructor taking localPos and screenPos. That puts localPos into the
         // event's localPos and windowPos, and screenPos into the event's screenPos. This way
         // the windowPos in e is ignored and is replaced by localPos. This is necessary
         // because QQuickWindow thinks of itself as a top-level window always.
         QMouseEvent mappedEvent(e->type(), e->localPos(), e->screenPos(), e->button(), e->buttons(), e->modifiers());
         QCoreApplication::sendEvent(m_quickWindow, &mappedEvent);
     }

     void WindowSingleThreaded::mouseReleaseEvent(QMouseEvent *e)
     {
         QMouseEvent mappedEvent(e->type(), e->localPos(), e->screenPos(), e->button(), e->buttons(), e->modifiers());
         QCoreApplication::sendEvent(m_quickWindow, &mappedEvent);
     }