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# bubble.cpp Example File
opengl/overpainting/bubble.cpp

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     #include <QtGui>

     #include "bubble.h"

     Bubble::Bubble(const QPointF &position, qreal radius, const QPointF &velocity)
         : position(position), vel(velocity), radius(radius)
     {
         innerColor = randomColor();
         outerColor = randomColor();
         updateBrush();
     }

     void Bubble::updateBrush()
     {
         QRadialGradient gradient(QPointF(radius, radius), radius,
                                  QPointF(radius*0.5, radius*0.5));

         gradient.setColorAt(0, QColor(255, 255, 255, 255));
         gradient.setColorAt(0.25, innerColor);
         gradient.setColorAt(1, outerColor);
         brush = QBrush(gradient);
     }

     void Bubble::drawBubble(QPainter *painter)
     {
         painter->save();
         painter->translate(position.x() - radius, position.y() - radius);
         painter->setBrush(brush);
         painter->drawEllipse(0, 0, int(2*radius), int(2*radius));
         painter->restore();
     }

     QColor Bubble::randomColor()
     {
         int red = int(205 + 50.0*qrand()/(RAND_MAX+1.0));
         int green = int(205 + 50.0*qrand()/(RAND_MAX+1.0));
         int blue = int(205 + 50.0*qrand()/(RAND_MAX+1.0));
         int alpha = int(91 + 100.0*qrand()/(RAND_MAX+1.0));

         return QColor(red, green, blue, alpha);
     }

     void Bubble::move(const QRect &bbox)
     {
         position += vel;
         qreal leftOverflow = position.x() - radius - bbox.left();
         qreal rightOverflow = position.x() + radius - bbox.right();
         qreal topOverflow = position.y() - radius - bbox.top();
         qreal bottomOverflow = position.y() + radius - bbox.bottom();

         if (leftOverflow < 0.0) {
             position.setX(position.x() - 2 * leftOverflow);
             vel.setX(-vel.x());
         } else if (rightOverflow > 0.0) {
             position.setX(position.x() - 2 * rightOverflow);
             vel.setX(-vel.x());
         }

         if (topOverflow < 0.0) {
             position.setY(position.y() - 2 * topOverflow);
             vel.setY(-vel.y());
         } else if (bottomOverflow > 0.0) {
             position.setY(position.y() - 2 * bottomOverflow);
             vel.setY(-vel.y());
         }
     }

     QRectF Bubble::rect()
     {
         return QRectF(position.x() - radius, position.y() - radius,
                       2 * radius, 2 * radius);
     }