Can someone explain what a Zbuffer is and what it's good for.

newbie,

It's used in 3D apps and is used so the polygons currently not in view are not drawn.

Peter

That's not really what it does, the Z buffer takes care of a problem called Z-fighting that occurs when two polygons have the same depth (z), if they do and a z buffer is not available, it will most likely flip between the two polygons and it's gonna look odd.

A z buffer stores the polygon depth and helps prevent z-fighting from occuring, it can also be used for hidden surface removal.

Edited by Daniel Netz at: 3/6/00 6:58:49 am

Actually Peter is right. Z-buffering is an algorithm that is used to help with hidden surface removal.

There is an alternate to the z-buffer algorithm, called the painter's algorithm. Its more complicated than z-buffers, but less intensive on the cpu. 

Technically, a z buffer is an screen buffer the same size as the video screen. For example, 640 x 480 matrix of 16 bit numbers for a 16 bit z-buffer, or integers, or whatever preicsion is needed.
All the polygons are projected onto the view plane, then the x,y values for the points in the plane correspond to coordinates in the z buffer. Then the color of the z value that is nearest to the view plane is stored in the z-buffer. After all is done, the z-buffer contains a finished image of what is to be displayed.

As for a pixel having two or more identical z values, then one would need to increase the precision of the z-buffer.