window_singlethreaded.cpp Example File

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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);
  }