From:	Chris Holmes <cholmes AT surfsouth DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: 3d
Date:	Sun, 08 Aug 1999 16:33:36 -0400
Organization:	Georgia Institute of Technology, Atlanta GA, USA
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Anthony Graham wrote:
> 
> I've got a 3d world thing working but i don't know to draw the faces in
> order, I've geen getting the vector that is the average (and so the center
> of my polygon (all of them are flat surfaces but the orientation varies))
> and using pythagoras determined the distance of this point from the camera's
> coordinates. After the shapes are drawn in descending distance order. This
> works only on simple shapes. This works fast but i need some more effective
> code which gives the correct order at most times.

  The Z coordinate (or depth into the screen) you should use is not the
average or center point, but by the extreme points.  

> the information available is the 3d coords of camera, and of all the 3d
> coords of each polygon. I've done the un-needed shape removal (off screen
> and back face culling). All i need to do is order the faces. If it makes it
> simpler you don't need to account for intersecting polygons as there will be
> none.

  So you know, "un-needed shape removal" is called HSR or Hidden Surface
Removal.  Back-face culling is a method of HSR.  So is Z-buffering
(which
is something I'm still clueless about).

> given the 3d coords of the flat polygons is there a quick way to see if a
> line (anywhere between 2 3d coords) goes through a 3d polygon? If the way of
> which you know only works for convex polygons (or any other restriction)
> tell me any way.

  I'm working on the math for that right now for something different.
I'll let you know what I come up with.

  Chris

-- 
I know that I will never be politically correct,
and I don't give a damn about my lack of etiquette!
-- Meatloaf

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