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();
 }