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

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     #include <QtGui>
     #include <QtOpenGL>

     #include <math.h>

     #include "glwidget.h"

     GLWidget::GLWidget(QWidget *parent)
         : QGLWidget(parent)
     {
         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);
     }

     GLWidget::~GLWidget()
     {
         makeCurrent();
         glDeleteLists(object, 1);
     }

     QSize GLWidget::minimumSizeHint() const
     {
         return QSize(50, 50);
     }

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

     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()
     {
         qglClearColor(trolltechPurple.dark());
         object = makeObject();
         glShadeModel(GL_FLAT);
         glEnable(GL_DEPTH_TEST);
         glEnable(GL_CULL_FACE);
     }

     void GLWidget::paintGL()
     {
         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);
     }

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

     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();
     }

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

         glBegin(GL_QUADS);

         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)
     {
         qglColor(trolltechGreen);

         glVertex3d(x1, y1, -0.05);
         glVertex3d(x2, y2, -0.05);
         glVertex3d(x3, y3, -0.05);
         glVertex3d(x4, y4, -0.05);

         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)));

         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;
     }