Rendering Multiple Viewports using GLUT

Question

Using OpenGL and GLUT, I want to render a scene from two different viewpoints. For the first viewpoint, it is a standard perspective projection using shaders. For the second viewpoint, it is a visualisation of the depth buffer. I want these two images to be contained within the same window, side-by-side.

So far, I have been using GLUT for display. For example, I use:

glutInitWindowSize(1000, 1000);
glutInitWindowPosition(500, 200);
glutCreateWindow("OpenGL Test");

This will draw my scene across the entire window for the one viewport which I have defined. But can I use GLUT to draw two different images from two different viewports, as described above? Or perhaps this is not so easy with just GLUT, and I will need to create a window natively in my operating system (I am using Ubuntu), and then define two different areas in that window which I should draw upon...

Thank you!

Nicol Bolas Nicol Bolas · Accepted Answer · 2015-12-28T04:38:04

GLUT ultimately has nothing to do with it. It creates and manages a window. What you do within that window is entirely up to you.

What you need to do is use the viewport transform. Because the viewport happens after clipping, no primitives outside of the range of the viewport transform will be rendered to (by drawing commands. Buffer clearing will still clear the whole framebuffer). This effectively defines the region of the window that all vertices will lie within.

So you call glViewport, specifying half of the window. Then you render the stuff you want in that half. Then you call glViewport to specify the other half. Then you render the stuff you want there. And then you're done; just swap buffers.

However, this also means that the typical tactic of only calling glViewport in your GLUT resize callback will not work. You must store the window's current size, then use that in your display function.

Rendering Multiple Viewports using GLUT

3 Answers