Re: 3d-model data structures.......

[Bob Pendleton <bobp@pendleton.com>]

Josiah Avery wrote:
> 
>   Hello,
> 
>   I was wondering if anyone had any suggestions on how to create the most
> effecient data structures to represent a 3d odject. The ways I  have been
> looking at where
> 
> 1. A collection of points.
> 2. A collection of faces.
> 3. A collection of unshared points ( ie a cube be though of as having 24
> points; 6 planes of 4 points a piece. But there are only really 8 points
> that are unique.

Generally you get the best results by using the layout supported by your
3D library. Having said the obvious and not to helpful answer... I have
to point out that any answer I give for that question will be wrong for
some combination of hardware and software.

By minimizing the number of points you minimize the number
transformations that have to be done. That can give you a speed boost on
some machines. By minimizing the number of points you can also reduce
the total size of the data. Having smaller data means there is less
chance of it being swapped out and again that can give you some extra
speed. Of course, minimizing the number of points can result in more
non-local references and result in lots of cache incoherency and cause a
significant loss of performance.

All that being said, I'm fond of using the minimal number of points with
things like lines and polygons and even complete objects being made up
of pointers to a set of shared points. So, a cube is made up of 8 points
referenced from either 6 quads or 12 triangles.

		Hope that helps

			Bob P.


> 
> If there are some other ways, I'd be glad to hear them. Also, if someone has
> any sample code, and is willing to share, that would be very cool.
> 
>      On a side note, if you guys haven't already, be sure and check out this
> new online game devlopment comic strip at www.badtech.com
> 
>    Thanks in advance.
> 
>    Josiah Avery
> 
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