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);
 }