Qt 5.7 | Qt GUI | Raster Window Example | rasterwindow.cpp Example File

Qt 5.7.1 Reference Documentation

# rasterwindow.cpp Example File

rasterwindow/rasterwindow.cpp

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      #include "rasterwindow.h"

      RasterWindow::RasterWindow(QWindow *parent)
          : QWindow(parent)
          , m_update_pending(false)
      {
          create();
          m_backingStore = new QBackingStore(this);

          setGeometry(100, 100, 300, 200);

      }

      bool RasterWindow::event(QEvent *event)
      {
          if (event->type() == QEvent::UpdateRequest) {
              m_update_pending = false;
              renderNow();
              return true;
          }
          return QWindow::event(event);
      }

      void RasterWindow::renderLater()
      {
          if (!m_update_pending) {
              m_update_pending = true;
              QCoreApplication::postEvent(this, new QEvent(QEvent::UpdateRequest));
          }
      }

      void RasterWindow::resizeEvent(QResizeEvent *resizeEvent)
      {
          m_backingStore->resize(resizeEvent->size());
          if (isExposed())
              renderNow();
      }

      void RasterWindow::exposeEvent(QExposeEvent *)
      {
          if (isExposed()) {
              renderNow();
          }
      }

      void RasterWindow::renderNow()
      {
          if (!isExposed())
              return;

          QRect rect(0, 0, width(), height());
          m_backingStore->beginPaint(rect);

          QPaintDevice *device = m_backingStore->paintDevice();
          QPainter painter(device);

          painter.fillRect(0, 0, width(), height(), Qt::white);
          render(&painter);

          m_backingStore->endPaint();
          m_backingStore->flush(rect);
      }

      void RasterWindow::render(QPainter *painter)
      {
          painter->drawText(QRectF(0, 0, width(), height()), Qt::AlignCenter, QStringLiteral("QWindow"));
      }