I'm sure the following applies to DirectX and OpenGL but I figured it'd get more attention here since most of you guys use OpenGL
While browsing through the DirectX SDK a while back, I found this neat little diagram:
What particularly interested me was this formula
D * tan(FOV / 2)
In short, the above function'll give us half the height of the viewing frustum at any given distance from the camera
How can this be useful? Say you're working on a 2.5D game such as I am (very spontaneously I might add >: ), and the screen in the players plane of movement has to be say, 800 x 600. With a little bit of work, we could rework the formula to give us this:
D = H / 2 / tan(FOV / 2)
D being the distance the camera needs to be from the movement plane, H being the height of the screen at said distance, and FOV being the field of view, which is normally Pi / [2, 3, or 4].
If you're using Pi/4, here's a little define with it all precalculated you can use like a function
#define GetZoom(DistanceH) (DistanceH / 2 / 0.4142135623730950488016887242097f)
Anywho, I'm off to work, 12 hour workdays are killer @_@
