问在Qt中绘制多色线条

EN

#include <QtGui>

class W: public QWidget {
    Q_OBJECT

    public:
        W(QWidget *parent = 0): QWidget(parent) {};

    protected:
        void paintEvent(QPaintEvent *) {
            QPainter p(this);

            // Draw boring background
            p.setPen(Qt::NoPen);
            p.setBrush(QColor(0,255,0));
            p.drawRect(0, 0, 30, 90);
            p.setBrush(QColor(255,0,0));
            p.drawRect(30, 0, 30, 90);
            p.setBrush(QColor(0,0,255));
            p.drawRect(60, 0, 30, 90);

            // This is the important part you'll want to play with
            p.setCompositionMode(QPainter::RasterOp_SourceAndNotDestination);
            QPen inverter(Qt::white);
            inverter.setWidth(10);
            p.setPen(inverter);
            p.drawLine(0, 0, 90, 90);
        }
};