Perspective `zoom' - where did it go?

Some time ago someone posted a tutorial for executing a zoom operation on a scene (calculating fov etc. from a rectangular area drawn out on the screen) - I can’t find the tut anywhere now.

Can someone point me in the correct direction please?


this can be done using the stencil buffer as following

  1. Render to stencil, not to frame buffer the shape of you zoom, a sphere or a quad
    setup the stencil buffer so that it write a 1 where it rendered

  2. Render your scene with normal fov but enable stenciltest so that it fails where the stencil is 1

  3. Render your scene with zoomed fov but enable stenciltest so that it succeds where the stencil is 1


[This message has been edited by ScottManDeath (edited 04-22-2002).]

Rectangles are also perfect candidates for the scissor test, so you don’t need to mess with the stencil buffer.

1)Disable scissor test
2)set normal projection
3)Draw non-zoomed stuff
4)set scissor rectangle
5)enable scissor test
6)clear depth
7)set up ‘zoom’ projection
8)render zoomed stuff