just get a black screen

Hi,
I try now for hours to understand why my screen is still black. I use qt to draw a simple quad. At first I tried a polygon in 2d. That worked. Here is the code

void GLtest::initializeGL()
{
glEnable(GL_DEPTH_TEST);
glEnable(GL_CULL_FACE);
glShadeModel(GL_SMOOTH);
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);
}
//! [6]

//! [7]
void GLtest::paintGL()
{
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
GLenum errorcode;
errorcode = glGetError();

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glColor3f(1,0,0);
errorcode = glGetError();
glBegin(GL_QUADS);
glVertex3f(400,400,-8);
glVertex3f(400,-400,8);
glVertex3f(-400,-400,-8);
glVertex3f(-400,400,8);
glEnd();
errorcode = glGetError();

  }

//! [7]

//! [8]
void GLtest::resizeGL(int width, int height)
{
int side = qMin(width, height);
glViewport((width - side) / 2, (height - side) / 2, side, side);

glMatrixMode(GL_PROJECTION);
glLoadIdentity();

#ifdef QT_OPENGL_ES_1
glOrthof(-0.5, +0.5, -0.5, +0.5, 4.0, 150.0);
#else
glOrtho(-0.5, +0.5, -0.5, +0.5, 4.0, 150.0);
#endif
glMatrixMode(GL_MODELVIEW);

}

It is a Problem I get often playing with opengl.Is there a short shecklist, what to do if the screen keeps beeing black? What is the minimal code to get this quad drawn in my window?

Thanks for help

I don’t use Qt, but You should probably call some function to swap buffers in your paintGL, or at least glFlush if you are using single buffered context

Thanks for fast answer. However I think, this is done by qt.
I tried some other code and got it working with this:

void GLtest::initializeGL()
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glEnable(GL_DEPTH_TEST);
glShadeModel (GL_SMOOTH);
}
//! [6]

//! [7]
void GLtest::paintGL()
{
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity ();

// We will draw things a little deeper into the screen
glTranslatef(0,0,-20);

glColor3f(1,0,0);

/* glBegin(GL_TRIANGLES);

    glVertex3f(0,2,0);
    glVertex3f(3,0,0);
    glVertex3f(-3,0,0);

glEnd();*/
glBegin(GL_QUADS);
    glVertex3f(0,0,0);
    glVertex3f(1,0,0);
    glVertex3f(1,1,0);
    glVertex3f(0,1,0);
glEnd();


  }

//! [7]

//! [8]
void GLtest::resizeGL(int width, int height)
{
glViewport (0, 0, (GLsizei) width, (GLsizei) height);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
gluPerspective(60.0, (GLfloat) width/(GLfloat) height, 1.0, 21.0);
glMatrixMode (GL_MODELVIEW);

}

So I will compare to find my mistake.

you are drawing outside the view frustum, so nothing will be visible

try glOrtho with near and far at -100 and 100
you’ll see something then