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helper.cpp Example File
^{opengl/2dpainting/helper.cpp}

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    **
    ** This file is part of the documentation of the Qt Toolkit.
    **
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    ** and appearing in the file LICENSE.GPL included in the packaging of
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    #include <QtGui>
    #include "helper.h"

    Helper::Helper()
    {
        QLinearGradient gradient(QPointF(50, -20), QPointF(80, 20));
        gradient.setColorAt(0.0, Qt::white);
        gradient.setColorAt(1.0, QColor(0xa6, 0xce, 0x39));

        background = QBrush(QColor(64, 32, 64));
        circleBrush = QBrush(gradient);
        circlePen = QPen(Qt::black);
        circlePen.setWidth(1);
        textPen = QPen(Qt::white);
        textFont.setPixelSize(50);
    }

    void Helper::paint(QPainter *painter, QPaintEvent *event, int elapsed)
    {
        painter->fillRect(event->rect(), background);
        painter->translate(100, 100);

        painter->save();
        painter->setBrush(circleBrush);
        painter->setPen(circlePen);
        painter->rotate(elapsed * 0.030);

        qreal r = elapsed/1000.0;
        int n = 30;
        for (int i = 0; i < n; ++i) {
            painter->rotate(30);
            qreal radius = 0 + 120.0*((i+r)/n);
            qreal circleRadius = 1 + ((i+r)/n)*20;
            painter->drawEllipse(QRectF(radius, -circleRadius,
                                        circleRadius*2, circleRadius*2));
        }
        painter->restore();

        painter->setPen(textPen);
        painter->setFont(textFont);
        painter->drawText(QRect(-50, -50, 100, 100), Qt::AlignCenter, "Qt");
    }