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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 "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()));

         object = 0;
         xRot = 0;
         yRot = 0;
         zRot = 0;

         trolltechGreen = QColor::fromCmykF(0.40, 0.0, 1.0, 0.0);
         trolltechPurple = 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()
     {
         makeCurrent();
         glDeleteLists(object, 1);
     }

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

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

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

     void GLWidget::initializeGL()
     {
         object = makeObject();
     }

     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(trolltechPurple.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();
         glTranslated(0.0, 0.0, -10.0);
         glRotated(xRot / 16.0, 1.0, 0.0, 0.0);
         glRotated(yRot / 16.0, 0.0, 1.0, 0.0);
         glRotated(zRot / 16.0, 0.0, 0.0, 1.0);
         glCallList(object);

         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);
     }

     GLuint GLWidget::makeObject()
     {
         GLuint list = glGenLists(1);
         glNewList(list, GL_COMPILE);

         glEnable(GL_NORMALIZE);
         glBegin(GL_QUADS);

         static GLfloat logoDiffuseColor[4] = {trolltechGreen.red()/255.0,
                                               trolltechGreen.green()/255.0,
                                               trolltechGreen.blue()/255.0, 1.0};
         glMaterialfv(GL_FRONT, GL_DIFFUSE, logoDiffuseColor);

         GLdouble x1 = +0.06;
         GLdouble y1 = -0.14;
         GLdouble x2 = +0.14;
         GLdouble y2 = -0.06;
         GLdouble x3 = +0.08;
         GLdouble y3 = +0.00;
         GLdouble x4 = +0.30;
         GLdouble y4 = +0.22;

         quad(x1, y1, x2, y2, y2, x2, y1, x1);
         quad(x3, y3, x4, y4, y4, x4, y3, x3);

         extrude(x1, y1, x2, y2);
         extrude(x2, y2, y2, x2);
         extrude(y2, x2, y1, x1);
         extrude(y1, x1, x1, y1);
         extrude(x3, y3, x4, y4);
         extrude(x4, y4, y4, x4);
         extrude(y4, x4, y3, x3);

         const double Pi = 3.14159265358979323846;
         const int NumSectors = 200;

         for (int i = 0; i < NumSectors; ++i) {
             double angle1 = (i * 2 * Pi) / NumSectors;
             GLdouble x5 = 0.30 * sin(angle1);
             GLdouble y5 = 0.30 * cos(angle1);
             GLdouble x6 = 0.20 * sin(angle1);
             GLdouble y6 = 0.20 * cos(angle1);

             double angle2 = ((i + 1) * 2 * Pi) / NumSectors;
             GLdouble x7 = 0.20 * sin(angle2);
             GLdouble y7 = 0.20 * cos(angle2);
             GLdouble x8 = 0.30 * sin(angle2);
             GLdouble y8 = 0.30 * cos(angle2);

             quad(x5, y5, x6, y6, x7, y7, x8, y8);

             extrude(x6, y6, x7, y7);
             extrude(x8, y8, x5, y5);
         }

         glEnd();

         glEndList();
         return list;
     }

     void GLWidget::quad(GLdouble x1, GLdouble y1, GLdouble x2, GLdouble y2,
                         GLdouble x3, GLdouble y3, GLdouble x4, GLdouble y4)
     {
         glNormal3d(0.0, 0.0, -1.0);
         glVertex3d(x1, y1, -0.05);
         glVertex3d(x2, y2, -0.05);
         glVertex3d(x3, y3, -0.05);
         glVertex3d(x4, y4, -0.05);

         glNormal3d(0.0, 0.0, 1.0);
         glVertex3d(x4, y4, +0.05);
         glVertex3d(x3, y3, +0.05);
         glVertex3d(x2, y2, +0.05);
         glVertex3d(x1, y1, +0.05);
     }

     void GLWidget::extrude(GLdouble x1, GLdouble y1, GLdouble x2, GLdouble y2)
     {
         qglColor(trolltechGreen.dark(250 + int(100 * x1)));

         glNormal3d((x1 + x2)/2.0, (y1 + y2)/2.0, 0.0);
         glVertex3d(x1, y1, +0.05);
         glVertex3d(x2, y2, +0.05);
         glVertex3d(x2, y2, -0.05);
         glVertex3d(x1, y1, -0.05);
     }

     void GLWidget::normalizeAngle(int *angle)
     {
         while (*angle < 0)
             *angle += 360 * 16;
         while (*angle > 360 * 16)
             *angle -= 360 * 16;
     }

     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();
         glOrtho(-0.5, +0.5, +0.5, -0.5, 4.0, 15.0);
         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);
     }