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

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     #include "glwidget.h"
     #include <math.h>

     #ifndef GL_MULTISAMPLE
     #define GL_MULTISAMPLE  0x809D
     #endif

     GLWidget::GLWidget(QWidget *parent)
         : QGLWidget(QGLFormat(QGL::SampleBuffers), parent)
     {
         startTimer(40);
         setWindowTitle(tr("Sample Buffers"));
     }

     void GLWidget::initializeGL()
     {
         glMatrixMode(GL_PROJECTION);
         glLoadIdentity();
         glOrtho(-.5, .5, .5, -.5, -1000, 1000);
         glMatrixMode(GL_MODELVIEW);
         glLoadIdentity();
         glClearColor(1.0f, 1.0f, 1.0f, 1.0f);

         makeObject();
     }

     void GLWidget::resizeGL(int w, int h)
     {
         glViewport(0, 0, w, h);
     }

     void GLWidget::paintGL()
     {
         static float rot = 0.0;
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

         glMatrixMode(GL_MODELVIEW);
         glPushMatrix();
         glEnable(GL_MULTISAMPLE);
         glTranslatef(-0.25f, -0.10f, 0.0f);
         glScalef(0.75f, 1.15f, 0.0f);
         glRotatef(rot, 0.0f, 0.f, 1.0f);
         glCallList(list);
         glPopMatrix();

         glPushMatrix();
         glDisable(GL_MULTISAMPLE);
         glTranslatef(0.25f, -0.10f, 0.0f);
         glScalef(0.75f, 1.15f, 0.0f);
         glRotatef(rot, 0.0f, 0.0f, 1.0f);
         glCallList(list);
         glPopMatrix();

         rot += 0.2f;

         qglColor(Qt::black);
         renderText(-0.35, 0.4, 0.0, "Multisampling enabled");
         renderText(0.15, 0.4, 0.0, "Multisampling disabled");
     }

     void GLWidget::timerEvent(QTimerEvent *)
     {
         update();
     }

     void GLWidget::makeObject()
     {
         QColor qtGreen(QColor::fromCmykF(0.40, 0.0, 1.0, 0.0));
         const double Pi = 3.14159265358979323846;
         const int NumSectors = 15;
         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;

         list = glGenLists(1);
         glNewList(list, GL_COMPILE);
         {
             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);

                 qglColor(qtGreen);
                 quad(GL_QUADS, x5, y5, x6, y6, x7, y7, x8, y8);
                 qglColor(Qt::black);
                 quad(GL_LINE_LOOP, x5, y5, x6, y6, x7, y7, x8, y8);
             }

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

             qglColor(Qt::black);
             quad(GL_LINE_LOOP, x1, y1, x2, y2, y2, x2, y1, x1);
             quad(GL_LINE_LOOP, x3, y3, x4, y4, y4, x4, y3, x3);
         }
         glEndList();
     }

     void GLWidget::quad(GLenum primitive, GLdouble x1, GLdouble y1, GLdouble x2, GLdouble y2,
                         GLdouble x3, GLdouble y3, GLdouble x4, GLdouble y4)
     {
         glBegin(primitive);
         {
             glVertex2d(x1, y1);
             glVertex2d(x2, y2);
             glVertex2d(x3, y3);
             glVertex2d(x4, y4);
         }
         glEnd();
     }