renderarea.cpp Example File
^{painting/basicdrawing/renderarea.cpp}

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 #include <QtGui>

 #include "renderarea.h"

 RenderArea::RenderArea(QWidget *parent)
     : QWidget(parent)
 {
     shape = Polygon;
     antialiased = false;
     transformed = false;
     pixmap.load(":/images/qt-logo.png");

     setBackgroundRole(QPalette::Base);
     setAutoFillBackground(true);
 }

 QSize RenderArea::minimumSizeHint() const
 {
     return QSize(100, 100);
 }

 QSize RenderArea::sizeHint() const
 {
     return QSize(400, 200);
 }

 void RenderArea::setShape(Shape shape)
 {
     this->shape = shape;
     update();
 }

 void RenderArea::setPen(const QPen &pen)
 {
     this->pen = pen;
     update();
 }

 void RenderArea::setBrush(const QBrush &brush)
 {
     this->brush = brush;
     update();
 }

 void RenderArea::setAntialiased(bool antialiased)
 {
     this->antialiased = antialiased;
     update();
 }

 void RenderArea::setTransformed(bool transformed)
 {
     this->transformed = transformed;
     update();
 }

 void RenderArea::paintEvent(QPaintEvent * /* event */)
 {
     static const QPoint points[4] = {
         QPoint(10, 80),
         QPoint(20, 10),
         QPoint(80, 30),
         QPoint(90, 70)
     };

     QRect rect(10, 20, 80, 60);

     QPainterPath path;
     path.moveTo(20, 80);
     path.lineTo(20, 30);
     path.cubicTo(80, 0, 50, 50, 80, 80);

     int startAngle = 30 * 16;
     int arcLength = 120 * 16;

     QPainter painter(this);
     painter.setPen(pen);
     painter.setBrush(brush);
     if (antialiased) {
         painter.setRenderHint(QPainter::Antialiasing, true);
         painter.translate(+0.5, +0.5);
     }

     for (int x = 0; x < width(); x += 100) {
         for (int y = 0; y < height(); y += 100) {
             painter.save();
             painter.translate(x, y);
             if (transformed) {
                 painter.translate(50, 50);
                 painter.rotate(60.0);
                 painter.scale(0.6, 0.9);
                 painter.translate(-50, -50);
             }

             switch (shape) {
             case Line:
                 painter.drawLine(rect.bottomLeft(), rect.topRight());
                 break;
             case Points:
                 painter.drawPoints(points, 4);
                 break;
             case Polyline:
                 painter.drawPolyline(points, 4);
                 break;
             case Polygon:
                 painter.drawPolygon(points, 4);
                 break;
             case Rect:
                 painter.drawRect(rect);
                 break;
             case RoundRect:
                 painter.drawRoundRect(rect);
                 break;
             case Ellipse:
                 painter.drawEllipse(rect);
                 break;
             case Arc:
                 painter.drawArc(rect, startAngle, arcLength);
                 break;
             case Chord:
                 painter.drawChord(rect, startAngle, arcLength);
                 break;
             case Pie:
                 painter.drawPie(rect, startAngle, arcLength);
                 break;
             case Path:
                 painter.drawPath(path);
                 break;
             case Text:
                 painter.drawText(rect, Qt::AlignCenter, tr("Qt by\nTrolltech"));
                 break;
             case Pixmap:
                 painter.drawPixmap(10, 10, pixmap);
             }
             painter.restore();
         }
     }

     painter.setPen(palette().dark().color());
     painter.setBrush(Qt::NoBrush);
     painter.drawRect(QRect(0, 0, width() - 1, height() - 1));
 }