glwidget.cpp Example File
^{opengl/overpainting/glwidget.cpp}

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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;
     painter.begin(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->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);
 }