QGL, opengl - all values of zaxis outside of 1;-1 get clipped - qt

Question

All figures outside of z-axis: (1;-1) range get clipped. Here is some code:
void MainWindow::initializeGL()
{
glDepthRange(-2,2);
glEnable(GL_TEXTURE_2D);
glDisable(GL_COLOR_MATERIAL);
glEnable(GL_BLEND);
glEnable(GL_POLYGON_SMOOTH);
//glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glClearColor(1, 1, 0, 0);
glDisable(GL_DEPTH_TEST); // Enables Depth Testing
glDepthFunc(GL_LESS); // The Type Of Depth Test To Do
glShadeModel(GL_SMOOTH); // Enables Smooth Color Shading
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
}
void MainWindow::paintGL(){
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
// glEnable(GL_TEXTURE_2D);
// glBindTexture(GL_TEXTURE_2D,texture);
// glTexSubImage2D(GL_TEXTURE_2D, 0, 0,0 , image.width(), image.height(), 0, 0, image.bits() );
//glMatrixMode(GL_MODELVIEW);
//glEnable(GL_DEPTH_TEST);
glTranslated(0.0, 0.0, 1.9);
qglColor(Qt::black);
glBegin(GL_TRIANGLES);
glVertex3d(-0.1,0.1,1);
glVertex3d(-0.1,-0.1,-1);
glVertex3d(0.1,-0.1,0);
glEnd();
}
Any idea why does it happen?

Answer 1

This is actually completely normal behavior.
When you use identity modelview and projection matrices, your coordinates are in clip-space. The default W value for a 3D vertex in OpenGL is 1.0 (vertices are always 4D), and clip-space -> NDC works by dividing each component of a vertex by its W component and then clipping anything with a coordinate outside the range [-1,1].
I think what is confusing you is the glDepthRange (...) call. That does not affect clipping. Depth range is part of the viewport transformation, which happens after clipping.