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

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     ** General Public License version 3.0 as published by the Free Software
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     #include <QtGui>
     #include <QtOpenGL>
     #include <stdlib.h>

     #include <math.h>

     #include "bubble.h"
     #include "qtlogo.h"
     #include "glwidget.h"

     #ifndef GL_MULTISAMPLE
     #define GL_MULTISAMPLE  0x809D
     #endif

     GLWidget::GLWidget(QWidget *parent)
         : QGLWidget(QGLFormat(QGL::SampleBuffers), parent)
     {
         QTime midnight(0, 0, 0);
         qsrand(midnight.secsTo(QTime::currentTime()));

         logo = 0;
         xRot = 0;
         yRot = 0;
         zRot = 0;

         qtGreen = QColor::fromCmykF(0.40, 0.0, 1.0, 0.0);
         qtPurple = QColor::fromCmykF(0.39, 0.39, 0.0, 0.0);

         animationTimer.setSingleShot(false);
         connect(&animationTimer, SIGNAL(timeout()), this, SLOT(animate()));
         animationTimer.start(25);

         setAutoFillBackground(false);
         setMinimumSize(200, 200);
         setWindowTitle(tr("Overpainting a Scene"));
     }

     GLWidget::~GLWidget()
     {
     }

     static void qNormalizeAngle(int &angle)
     {
         while (angle < 0)
             angle += 360 * 16;
         while (angle > 360 * 16)
             angle -= 360 * 16;
     }

     void GLWidget::setXRotation(int angle)
     {
         qNormalizeAngle(angle);
         if (angle != xRot)
             xRot = angle;
     }

     void GLWidget::setYRotation(int angle)
     {
         qNormalizeAngle(angle);
         if (angle != yRot)
             yRot = angle;
     }

     void GLWidget::setZRotation(int angle)
     {
         qNormalizeAngle(angle);
         if (angle != zRot)
             zRot = angle;
     }

     void GLWidget::initializeGL()
     {
         glEnable(GL_MULTISAMPLE);

         logo = new QtLogo(this);
         logo->setColor(qtGreen.dark());
     }

     void GLWidget::mousePressEvent(QMouseEvent *event)
     {
         lastPos = event->pos();
     }

     void GLWidget::mouseMoveEvent(QMouseEvent *event)
     {
         int dx = event->x() - lastPos.x();
         int dy = event->y() - lastPos.y();

         if (event->buttons() & Qt::LeftButton) {
             setXRotation(xRot + 8 * dy);
             setYRotation(yRot + 8 * dx);
         } else if (event->buttons() & Qt::RightButton) {
             setXRotation(xRot + 8 * dy);
             setZRotation(zRot + 8 * dx);
         }
         lastPos = event->pos();
     }

     void GLWidget::paintEvent(QPaintEvent *event)
     {
         makeCurrent();
         glMatrixMode(GL_MODELVIEW);
         glPushMatrix();

         qglClearColor(qtPurple.dark());
         glShadeModel(GL_SMOOTH);
         glEnable(GL_DEPTH_TEST);
         glEnable(GL_CULL_FACE);
         glEnable(GL_LIGHTING);
         glEnable(GL_LIGHT0);
         glEnable(GL_MULTISAMPLE);
         static GLfloat lightPosition[4] = { 0.5, 5.0, 7.0, 1.0 };
         glLightfv(GL_LIGHT0, GL_POSITION, lightPosition);

         setupViewport(width(), height());

         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
         glLoadIdentity();
         glTranslatef(0.0, 0.0, -10.0);
         glRotatef(xRot / 16.0, 1.0, 0.0, 0.0);
         glRotatef(yRot / 16.0, 0.0, 1.0, 0.0);
         glRotatef(zRot / 16.0, 0.0, 0.0, 1.0);

         logo->draw();

         glShadeModel(GL_FLAT);
         glDisable(GL_CULL_FACE);
         glDisable(GL_DEPTH_TEST);
         glDisable(GL_LIGHTING);

         glMatrixMode(GL_MODELVIEW);
         glPopMatrix();

         QPainter painter(this);
         painter.setRenderHint(QPainter::Antialiasing);
         foreach (Bubble *bubble, bubbles) {
             if (bubble->rect().intersects(event->rect()))
                 bubble->drawBubble(&painter);
         }
         drawInstructions(&painter);
         painter.end();
     }

     void GLWidget::resizeGL(int width, int height)
     {
         setupViewport(width, height);
     }

     void GLWidget::showEvent(QShowEvent *event)
     {
         Q_UNUSED(event);
         createBubbles(20 - bubbles.count());
     }

     QSize GLWidget::sizeHint() const
     {
         return QSize(400, 400);
     }

     void GLWidget::createBubbles(int number)
     {
         for (int i = 0; i < number; ++i) {
             QPointF position(width()*(0.1 + (0.8*qrand()/(RAND_MAX+1.0))),
                             height()*(0.1 + (0.8*qrand()/(RAND_MAX+1.0))));
             qreal radius = qMin(width(), height())*(0.0125 + 0.0875*qrand()/(RAND_MAX+1.0));
             QPointF velocity(width()*0.0125*(-0.5 + qrand()/(RAND_MAX+1.0)),
                             height()*0.0125*(-0.5 + qrand()/(RAND_MAX+1.0)));

             bubbles.append(new Bubble(position, radius, velocity));
         }
     }

     void GLWidget::animate()
     {
         QMutableListIterator<Bubble*> iter(bubbles);

         while (iter.hasNext()) {
             Bubble *bubble = iter.next();
             bubble->move(rect());
         }
         update();
     }

     void GLWidget::setupViewport(int width, int height)
     {
         int side = qMin(width, height);
         glViewport((width - side) / 2, (height - side) / 2, side, side);

         glMatrixMode(GL_PROJECTION);
         glLoadIdentity();
     #ifdef QT_OPENGL_ES
         glOrthof(-0.5, +0.5, -0.5, 0.5, 4.0, 15.0);
     #else
         glOrtho(-0.5, +0.5, -0.5, 0.5, 4.0, 15.0);
     #endif
         glMatrixMode(GL_MODELVIEW);
     }

     void GLWidget::drawInstructions(QPainter *painter)
     {
         QString text = tr("Click and drag with the left mouse button "
                           "to rotate the Qt logo.");
         QFontMetrics metrics = QFontMetrics(font());
         int border = qMax(4, metrics.leading());

         QRect rect = metrics.boundingRect(0, 0, width() - 2*border, int(height()*0.125),
                                           Qt::AlignCenter | Qt::TextWordWrap, text);
         painter->setRenderHint(QPainter::TextAntialiasing);
         painter->fillRect(QRect(0, 0, width(), rect.height() + 2*border),
                          QColor(0, 0, 0, 127));
         painter->setPen(Qt::white);
         painter->fillRect(QRect(0, 0, width(), rect.height() + 2*border),
                           QColor(0, 0, 0, 127));
         painter->drawText((width() - rect.width())/2, border,
                           rect.width(), rect.height(),
                           Qt::AlignCenter | Qt::TextWordWrap, text);
     }