Quick method for determining if something is on screen?

Started by elias4444, July 17, 2006, 19:04:01

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I'm working on optimizing my game, and was wondering if there was a quick/easy way to determine if an object is viewable on screen or not (to determine if it should be drawn or not). I know culling can determine if a face is forward facing or not, but is there another method for determining if something is within the viewport?


how about object-culling with
-just a list with all objects, making a frustum-culling-test against their boundingbox (the trees do the same, only with less tests)



My main issue is just trying to come up with some sort of math that determines if something is "on-screen" or not. This isn't an orthographic game, so it gets a bit complicated. I'm at a loss as to how to determine it.  :(


regardless which type of rendering you use, you always have some sort of viewfrustrum. which can be a box, a frustrum of pyramid (in a usual 3D game), a 2D rectangle in a 2D game, etc. the type of your frustrum is determind by the projectionmatrix.

now you can use your frustrum culling it with the boundingbox of your objects (in 2D for example a 2D rectangle, in 3D a 3D box, or a 3D sphere).

if your frustrum intersects the boundingbox of the object, the object or a part of it is visible - "on screen".

look for some tutorials, how to compute the intersection of a frustrum and a box or whatever.

http://www.realtimerendering.com/int/ here you can find an overview over some intersection computations and where they are listed.

Fool Running

you need to do Frustum-culling (like funsheep said :D ) to determine if a 3D object is in the view frustum. You should be able to search Google to find examples on how to do this.

EDIT: Nevermind, Funsheep beat me :lol:
Programmers will, one day, rule the world... and the world won't notice until its too late.Just testing the marquee option ;D


Look @ here, he uses some functions that might interest you.