SVG Generator Example

The DisplayWidget Class

The DisplayWidget class displays a drawing consisting of a selection of elements chosen by the user. These are defined using Shape and Background enums that are included within the class definition:

 class DisplayWidget : public QWidget
 {
     Q_OBJECT

 public:
     enum Shape { House = 0, Car = 1 };
     enum Background { Sky = 0, Trees = 1, Road = 2 };

     DisplayWidget(QWidget *parent = 0);
     QColor color() const;
     void paint(QPainter &painter);

 public slots:
     void setBackground(Background background);
     void setColor(const QColor &color);
     void setShape(Shape shape);

 protected:
     void paintEvent(QPaintEvent *event);

 private:
     Background background;
     QColor shapeColor;
     Shape shape;
     QHash<Shape,QPainterPath> shapeMap;
     QPainterPath moon;
     QPainterPath tree;
 };

Much of this class is used to configure the appearance of the drawing. The paintEvent() and paint() functions are most relevant to the purpose of this example, so we will describe these here and leave the reader to look at the source code for the example to see how shapes and colors are handled.

We reimplement the QWidget::paintEvent() function to display the drawing on screen:

 void DisplayWidget::paintEvent(QPaintEvent * /* event */)
 {
     QPainter painter;
     painter.begin(this);
     painter.setRenderHint(QPainter::Antialiasing);
     paint(painter);
     painter.end();
 }

Here, we only construct a QPainter object, begin painting on the device and set a render hint for improved output quality before calling the paint() function to perform the painting itself. When this returns, we close the painter and return.

The paint() function is designed to be used for different painting tasks. In this example, we use it to draw on a DisplayWidget instance and on a QSvgGenerator object. We show how the painting is performed to demonstrate that there is nothing device-specific about the process:

 void DisplayWidget::paint(QPainter &painter)
 {
     painter.setClipRect(QRect(0, 0, 200, 200));
     painter.setPen(Qt::NoPen);

     switch (background) {
     case Sky:
     default:
         painter.fillRect(QRect(0, 0, 200, 200), Qt::darkBlue);
         painter.translate(145, 10);
         painter.setBrush(Qt::white);
         painter.drawPath(moon);
         painter.translate(-145, -10);
         break;
     case Trees:
     {
         painter.fillRect(QRect(0, 0, 200, 200), Qt::darkGreen);
         painter.setBrush(Qt::green);
         painter.setPen(Qt::black);
         for (int y = -55, row = 0; y < 200; y += 50, ++row) {
             int xs;
             if (row == 2 || row == 3)
                 xs = 150;
             else
                 xs = 50;
             for (int x = 0; x < 200; x += xs) {
                 painter.save();
                 painter.translate(x, y);
                 painter.drawPath(tree);
                 painter.restore();
             }
         }
         break;
     }
     case Road:
         painter.fillRect(QRect(0, 0, 200, 200), Qt::gray);
         painter.setPen(QPen(Qt::white, 4, Qt::DashLine));
         painter.drawLine(QLine(0, 35, 200, 35));
         painter.drawLine(QLine(0, 165, 200, 165));
         break;
     }

     painter.setBrush(shapeColor);
     painter.setPen(Qt::black);
     painter.translate(100, 100);
     painter.drawPath(shapeMap[shape]);
 }

 class Window : public QWidget, private Ui::Window
 {
     Q_OBJECT

 public:
     Window(QWidget *parent = 0);

 public slots:
     void saveSvg();
     void updateBackground(int background);
     void updateColor();
     void updateShape(int shape);

 private:
     QString path;
 };

 void Window::saveSvg()
 {
     QString newPath = QFileDialog::getSaveFileName(this, tr("Save SVG"),
         path, tr("SVG files (*.svg)"));

     if (newPath.isEmpty())
         return;

     path = newPath;

     QSvgGenerator generator;
     generator.setFileName(path);
     generator.setSize(QSize(200, 200));
     generator.setViewBox(QRect(0, 0, 200, 200));
     generator.setTitle(tr("SVG Generator Example Drawing"));
     generator.setDescription(tr("An SVG drawing created by the SVG Generator "
                                 "Example provided with Qt."));
     QPainter painter;
     painter.begin(&generator);
     displayWidget->paint(painter);
     painter.end();
 }