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);
 }