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

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     #include <QtGui>
     #include <QtOpenGL>

     #include <math.h>

     #include "glwidget.h"

     GLWidget::GLWidget(QWidget *parent)
         : QGLWidget(parent)
     {
         gear1 = 0;
         gear2 = 0;
         gear3 = 0;
         xRot = 0;
         yRot = 0;
         zRot = 0;
         gear1Rot = 0;

         QTimer *timer = new QTimer(this);
         connect(timer, SIGNAL(timeout()), this, SLOT(advanceGears()));
         timer->start(20);
     }

     GLWidget::~GLWidget()
     {
         makeCurrent();
         glDeleteLists(gear1, 1);
         glDeleteLists(gear2, 1);
         glDeleteLists(gear3, 1);
     }

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

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

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

     void GLWidget::initializeGL()
     {
         static const GLfloat lightPos[4] = { 5.0f, 5.0f, 10.0f, 1.0f };
         static const GLfloat reflectance1[4] = { 0.8f, 0.1f, 0.0f, 1.0f };
         static const GLfloat reflectance2[4] = { 0.0f, 0.8f, 0.2f, 1.0f };
         static const GLfloat reflectance3[4] = { 0.2f, 0.2f, 1.0f, 1.0f };

         glLightfv(GL_LIGHT0, GL_POSITION, lightPos);
         glEnable(GL_LIGHTING);
         glEnable(GL_LIGHT0);
         glEnable(GL_DEPTH_TEST);

         gear1 = makeGear(reflectance1, 1.0, 4.0, 1.0, 0.7, 20);
         gear2 = makeGear(reflectance2, 0.5, 2.0, 2.0, 0.7, 10);
         gear3 = makeGear(reflectance3, 1.3, 2.0, 0.5, 0.7, 10);

         glEnable(GL_NORMALIZE);
         glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
     }

     void GLWidget::paintGL()
     {
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

         glPushMatrix();
         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);

         drawGear(gear1, -3.0, -2.0, 0.0, gear1Rot / 16.0);
         drawGear(gear2, +3.1, -2.0, 0.0, -2.0 * (gear1Rot / 16.0) - 9.0);

         glRotated(+90.0, 1.0, 0.0, 0.0);
         drawGear(gear3, -3.1, -1.8, -2.2, +2.0 * (gear1Rot / 16.0) - 2.0);

         glPopMatrix();
     }

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

         glMatrixMode(GL_PROJECTION);
         glLoadIdentity();
         glFrustum(-1.0, +1.0, -1.0, 1.0, 5.0, 60.0);
         glMatrixMode(GL_MODELVIEW);
         glLoadIdentity();
         glTranslated(0.0, 0.0, -40.0);
     }

     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::advanceGears()
     {
         gear1Rot += 2 * 16;
         updateGL();
     }

     GLuint GLWidget::makeGear(const GLfloat *reflectance, GLdouble innerRadius,
                               GLdouble outerRadius, GLdouble thickness,
                               GLdouble toothSize, GLint toothCount)
     {
         const double Pi = 3.14159265358979323846;

         GLuint list = glGenLists(1);
         glNewList(list, GL_COMPILE);
         glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, reflectance);

         GLdouble r0 = innerRadius;
         GLdouble r1 = outerRadius - toothSize / 2.0;
         GLdouble r2 = outerRadius + toothSize / 2.0;
         GLdouble delta = (2.0 * Pi / toothCount) / 4.0;
         GLdouble z = thickness / 2.0;
         int i, j;

         glShadeModel(GL_FLAT);

         for (i = 0; i < 2; ++i) {
             GLdouble sign = (i == 0) ? +1.0 : -1.0;

             glNormal3d(0.0, 0.0, sign);

             glBegin(GL_QUAD_STRIP);
             for (j = 0; j <= toothCount; ++j) {
                 GLdouble angle = 2.0 * Pi * j / toothCount;
                 glVertex3d(r0 * cos(angle), r0 * sin(angle), sign * z);
                 glVertex3d(r1 * cos(angle), r1 * sin(angle), sign * z);
                 glVertex3d(r0 * cos(angle), r0 * sin(angle), sign * z);
                 glVertex3d(r1 * cos(angle + 3 * delta), r1 * sin(angle + 3 * delta),
                            sign * z);
             }
             glEnd();

             glBegin(GL_QUADS);
             for (j = 0; j < toothCount; ++j) {
                 GLdouble angle = 2.0 * Pi * j / toothCount;
                 glVertex3d(r1 * cos(angle), r1 * sin(angle), sign * z);
                 glVertex3d(r2 * cos(angle + delta), r2 * sin(angle + delta),
                            sign * z);
                 glVertex3d(r2 * cos(angle + 2 * delta), r2 * sin(angle + 2 * delta),
                            sign * z);
                 glVertex3d(r1 * cos(angle + 3 * delta), r1 * sin(angle + 3 * delta),
                            sign * z);
             }
             glEnd();
         }

         glBegin(GL_QUAD_STRIP);
         for (i = 0; i < toothCount; ++i) {
             for (j = 0; j < 2; ++j) {
                 GLdouble angle = 2.0 * Pi * (i + (j / 2.0)) / toothCount;
                 GLdouble s1 = r1;
                 GLdouble s2 = r2;
                 if (j == 1)
                     qSwap(s1, s2);

                 glNormal3d(cos(angle), sin(angle), 0.0);
                 glVertex3d(s1 * cos(angle), s1 * sin(angle), +z);
                 glVertex3d(s1 * cos(angle), s1 * sin(angle), -z);

                 glNormal3d(s2 * sin(angle + delta) - s1 * sin(angle),
                            s1 * cos(angle) - s2 * cos(angle + delta), 0.0);
                 glVertex3d(s2 * cos(angle + delta), s2 * sin(angle + delta), +z);
                 glVertex3d(s2 * cos(angle + delta), s2 * sin(angle + delta), -z);
             }
         }
         glVertex3d(r1, 0.0, +z);
         glVertex3d(r1, 0.0, -z);
         glEnd();

         glShadeModel(GL_SMOOTH);

         glBegin(GL_QUAD_STRIP);
         for (i = 0; i <= toothCount; ++i) {
             GLdouble angle = i * 2.0 * Pi / toothCount;
             glNormal3d(-cos(angle), -sin(angle), 0.0);
             glVertex3d(r0 * cos(angle), r0 * sin(angle), +z);
             glVertex3d(r0 * cos(angle), r0 * sin(angle), -z);
         }
         glEnd();

         glEndList();

         return list;
     }

     void GLWidget::drawGear(GLuint gear, GLdouble dx, GLdouble dy, GLdouble dz,
                             GLdouble angle)
     {
         glPushMatrix();
         glTranslated(dx, dy, dz);
         glRotated(angle, 0.0, 0.0, 1.0);
         glCallList(gear);
         glPopMatrix();
     }

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