Multiple Views

Multiple projections can also be used for multiple views of a scene.

Different views typically occupy different regions of the screen.

This is accomplished using viewports.
In OpenGL, the "scissor test" is also needed.

Define the region of the window to use as follows:

    glViewport(x, y, width, height)
    glScissor(x, y, width, height)
    glEnable(GL_SCISSOR_TEST)