Cylinder draw using QT opengl functions

[YuriyRusinov]

Dear colleagues !

I want to draw cylinder on QGLWidget. I do

...
void GLWidget :: initializeGL (void)
{
    qDebug () << __FUNCTION__;
    glClearColor (1.0, 1.0, 1.0, 0.0);
}
 
void GLWidget :: paintGL (void)
{
    qDebug () << __FUNCTION__ << cyl_radius << cyl_height;
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    if (fabs (cyl_radius) < 0.1e-15 || fabs (cyl_height) < 0.1e-15)
        return;
    glBegin (GL_POLYGON);
    glColor3d (1, 0, 0);
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity();
    GLUquadricObj* q = gluNewQuadric ();
 
    gluCylinder (q, (GLdouble)cyl_radius, (GLdouble)cyl_radius, (GLdouble)cyl_height, 320, 320);
    glEnd ();
    glMatrixMode (GL_MODELVIEW);
    gluDeleteQuadric (q);
}
 
void GLWidget :: resizeGL (int width, int height)
{
    qDebug () << __FUNCTION__;
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    glViewport ((GLsizei)width/2, (GLsizei)height/2, (GLsizei)width, (GLsizei)height);
    glOrtho (0, this->QGLWidget::width (), 0, this->QGLWidget::height (), -1,1);
    glMatrixMode (GL_MODELVIEW);
}

...
void GLWidget :: initializeGL (void)
{
    qDebug () << __FUNCTION__;
    glClearColor (1.0, 1.0, 1.0, 0.0);
}

void GLWidget :: paintGL (void)
{
    qDebug () << __FUNCTION__ << cyl_radius << cyl_height;
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    if (fabs (cyl_radius) < 0.1e-15 || fabs (cyl_height) < 0.1e-15)
        return;
    glBegin (GL_POLYGON);
    glColor3d (1, 0, 0);
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity();
    GLUquadricObj* q = gluNewQuadric ();

    gluCylinder (q, (GLdouble)cyl_radius, (GLdouble)cyl_radius, (GLdouble)cyl_height, 320, 320);
    glEnd ();
    glMatrixMode (GL_MODELVIEW);
    gluDeleteQuadric (q);
}

void GLWidget :: resizeGL (int width, int height)
{
    qDebug () << __FUNCTION__;
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    glViewport ((GLsizei)width/2, (GLsizei)height/2, (GLsizei)width, (GLsizei)height);
    glOrtho (0, this->QGLWidget::width (), 0, this->QGLWidget::height (), -1,1);
    glMatrixMode (GL_MODELVIEW);
}

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But except cylinder I receive sector of circle as presented in attachment.

[jacek]

Maybe something is wrong with the projection? What happens when you draw a cylinder with smaller height? Also remove line #16.