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# helper.cpp Example File
opengl/2dpainting/helper.cpp

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        **
        ** Copyright (C) 2006-2006 Trolltech AS. All rights reserved.
        **
        ** This file is part of the documentation of the Qt Toolkit.
        **
        ** This file may be used under the terms of the GNU General Public
        ** License version 2.0 as published by the Free Software Foundation
        ** and appearing in the file LICENSE.GPL included in the packaging of
        ** this file.  Please review the following information to ensure GNU
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        ** http://www.trolltech.com/products/qt/opensource.html
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        ** review the following information:
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        ** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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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");
        }