Question

Assuming I use Orhographic Projection, and have a reshape function like this:

void reshape(f32 width, f32 height){
    aspect = width/height;
    glViewport(0, 0, width, height);
    // guaranted 960x640 HUD canvas
    if(640*aspect>=960){
        ortho.x = 640*aspect;
        ortho.y = 640;
    }else{
        ortho.x = 960;
        ortho.y = 960/aspect;
    }
    glOrtho(0, ortho.x, ortho.y, 0, -1.0f, 1.0f);
}

How can I make sure, that all vertices >ortho.x or >ortho.y (normally offscreen) are didn’t drawn?
Because if I scale the windows to something with a bigger aspect ratio than 1.5f (960/640) I see the objects, that schouldn’t be full visible (because the viewport is so big like the window).
Is there something like a clipping pane in orthographic projection?

Answer 1

What you want is to use [glScissor][1] to ensure that the rendered area never goes beyond a certain size. glScissor takes a rectangle in window coordinates (remember: window coordinates have the origin at the bottom-left). The scissor test prevents the generation of fragments outside of this area.

To activate the scissor test, you must use glEnable(GL_SCISSOR). Unless you do that, the above call won’t actually do anything.