window.cpp Example File

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  #include "window.h"

  #include <private/qguiapplication_p.h>

  #include <QBackingStore>
  #include <QPainter>
  #include <QtWidgets>

  static int colorIndexId = 0;

  QColor colorTable[] =
  {
      QColor("#f09f8f"),
      QColor("#a2bff2"),
      QColor("#c0ef8f")
  };

  Window::Window(QScreen *screen)
      : QWindow(screen)
      , m_backgroundColorIndex(colorIndexId++)
      , m_backingStore(0)
  {
      initialize();
  }

  Window::Window(QWindow *parent)
      : QWindow(parent)
      , m_backgroundColorIndex(colorIndexId++)
      , m_backingStore(0)
  {
      initialize();
  }

  void Window::initialize()
  {
      if (parent())
          setGeometry(QRect(160, 120, 320, 240));
      else {
          setGeometry(QRect(10, 10, 640, 480));

          setSizeIncrement(QSize(10, 10));
          setBaseSize(QSize(640, 480));
          setMinimumSize(QSize(240, 160));
          setMaximumSize(QSize(800, 600));
      }

      setFlags(flags() | Qt::SubWindow); // Don't create a toplevel window.

      create();
      m_backingStore = new QBackingStore(this);

      m_image = QImage(geometry().size(), QImage::Format_RGB32);
      m_image.fill(colorTable[m_backgroundColorIndex % (sizeof(colorTable) / sizeof(colorTable[0]))].rgba());

      m_lastPos = QPoint(-1, -1);
      m_renderTimer = 0;
  }

  void Window::mousePressEvent(QMouseEvent *event)
  {
      m_lastPos = event->pos();
  }

  void Window::mouseMoveEvent(QMouseEvent *event)
  {
      if (m_lastPos != QPoint(-1, -1)) {
          QPainter p(&m_image);
          p.setRenderHint(QPainter::Antialiasing);
          p.drawLine(m_lastPos, event->pos());
          m_lastPos = event->pos();
      }

      scheduleRender();
  }

  void Window::mouseReleaseEvent(QMouseEvent *event)
  {
      if (m_lastPos != QPoint(-1, -1)) {
          QPainter p(&m_image);
          p.setRenderHint(QPainter::Antialiasing);
          p.drawLine(m_lastPos, event->pos());
          m_lastPos = QPoint(-1, -1);
      }

      scheduleRender();
  }

  void Window::exposeEvent(QExposeEvent *)
  {
      scheduleRender();
  }

  void Window::resizeEvent(QResizeEvent *)
  {
      QImage old = m_image;

      //qDebug() << "Window::resizeEvent" << width << height;

      int width = qMax(geometry().width(), old.width());
      int height = qMax(geometry().height(), old.height());

      if (width > old.width() || height > old.height()) {
          m_image = QImage(width, height, QImage::Format_RGB32);
          m_image.fill(colorTable[(m_backgroundColorIndex) % (sizeof(colorTable) / sizeof(colorTable[0]))].rgba());

          QPainter p(&m_image);
          p.drawImage(0, 0, old);
      }

      render();
  }

  void Window::keyPressEvent(QKeyEvent *event)
  {
      switch (event->key()) {
      case Qt::Key_Backspace:
          m_text.chop(1);
          break;
      case Qt::Key_Enter:
      case Qt::Key_Return:
          m_text.append('\n');
          break;
      default:
          m_text.append(event->text());
          break;
      }
      scheduleRender();
  }

  void Window::scheduleRender()
  {
      if (!m_renderTimer)
          m_renderTimer = startTimer(1);
  }

  void Window::timerEvent(QTimerEvent *)
  {
      render();
      killTimer(m_renderTimer);
      m_renderTimer = 0;
  }

  void Window::render()
  {
      if (!m_backingStore)
          return;
      QRect rect(QPoint(), geometry().size());

      m_backingStore->resize(rect.size());

      m_backingStore->beginPaint(rect);

      QPaintDevice *device = m_backingStore->paintDevice();

      QPainter p(device);
      p.drawImage(0, 0, m_image);

      QFont font;
      font.setPixelSize(32);

      p.setFont(font);
      p.drawText(rect, 0, m_text);

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