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

     /****************************************************************************
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     ** Copyright (C) 2006-2006 Trolltech ASA. All rights reserved.
     **
     ** This file is part of the example classes 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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     ** 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");
     }