Qt 5.11 | Qt Quick | QQuickRenderControl Example | window_singlethreaded.cpp Example File

Qt 5.11.3 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);
      }