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# lighting.cpp Example File
effects/lighting/lighting.cpp

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     #include "lighting.h"

     #include <QtGui>

     #ifndef M_PI
     #define M_PI 3.14159265358979323846
     #endif

     Lighting::Lighting(QWidget *parent): QGraphicsView(parent), angle(0.0)
     {
         setScene(&m_scene);

         setupScene();

         QTimer *timer = new QTimer(this);
         connect(timer, SIGNAL(timeout()), SLOT(animate()));
         timer->setInterval(30);
         timer->start();

         setRenderHint(QPainter::Antialiasing, true);
         setFrameStyle(QFrame::NoFrame);
     }

     void Lighting::setupScene()
     {
         m_scene.setSceneRect(-300, -200, 600, 460);

         QLinearGradient linearGrad(QPointF(-100, -100), QPointF(100, 100));
         linearGrad.setColorAt(0, QColor(255, 255, 255));
         linearGrad.setColorAt(1, QColor(192, 192, 255));
         setBackgroundBrush(linearGrad);

         QRadialGradient radialGrad(30, 30, 30);
         radialGrad.setColorAt(0, Qt::yellow);
         radialGrad.setColorAt(0.2, Qt::yellow);
         radialGrad.setColorAt(1, Qt::transparent);
         QPixmap pixmap(60, 60);
         pixmap.fill(Qt::transparent);
         QPainter painter(&pixmap);
         painter.setPen(Qt::NoPen);
         painter.setBrush(radialGrad);
         painter.drawEllipse(0, 0, 60, 60);
         painter.end();

         m_lightSource = m_scene.addPixmap(pixmap);
         m_lightSource->setZValue(2);

         for (int i = -2; i < 3; ++i)
             for (int j = -2; j < 3; ++j) {
                 QAbstractGraphicsShapeItem *item;
                 if ((i + j) & 1)
                     item = new QGraphicsEllipseItem(0, 0, 50, 50);
                 else
                     item = new QGraphicsRectItem(0, 0, 50, 50);

                 item->setPen(QPen(Qt::black, 1));
                 item->setBrush(QBrush(Qt::white));
                 QGraphicsDropShadowEffect *effect = new QGraphicsDropShadowEffect;
                 effect->setBlurRadius(8);
                 item->setGraphicsEffect(effect);
                 item->setZValue(1);
                 item->setPos(i * 80, j * 80);
                 m_scene.addItem(item);
                 m_items << item;
             }

     }

     void Lighting::animate()
     {
         angle += (M_PI / 30);
         qreal xs = 200 * sin(angle) - 40 + 25;
         qreal ys = 200 * cos(angle) - 40 + 25;
         m_lightSource->setPos(xs, ys);

         for (int i = 0; i < m_items.size(); ++i) {
             QGraphicsItem *item = m_items.at(i);
             Q_ASSERT(item);
             QGraphicsDropShadowEffect *effect = static_cast<QGraphicsDropShadowEffect *>(item->graphicsEffect());
             Q_ASSERT(effect);

             QPointF delta(item->x() - xs, item->y() - ys);
             effect->setOffset(delta.toPoint() / 30);

             qreal dx = delta.x();
             qreal dy = delta.y();
             qreal dd = sqrt(dx * dx + dy * dy);
             QColor color = effect->color();
             color.setAlphaF(qBound(0.4, 1 - dd / 200.0, 0.7));
             effect->setColor(color);
         }

         m_scene.update();
     }