Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!glacier!jbn
From: jbn@glacier.STANFORD.EDU (John B. Nagle)
Newsgroups: comp.graphics
Subject: Re: Point Graphics
Message-ID: <17360@glacier.STANFORD.EDU>
Date: 15 Mar 88 17:19:38 GMT
References: <165500005@uiucdcsb>
Reply-To: jbn@glacier.UUCP (John B. Nagle)
Organization: Stanford University
Lines: 28
Keywords: Z-buffer, smart pixels


     Hidden surface elimination is often performed in hardware by
storing a Z value for each pixel and updating pixels in such a way that
points further than the one already stored at a given X,Y do not update
the screen, while nearer points update both the screen and the Z value.
This is called a Z-buffer.  A number of high-end graphics machines have
Z-buffers, including the high-end HP and Apollo solid modelling workstations.
Matrox makes a graphics board set for the IBM PC that includes a Z-buffer.

     Collision detection in 2D is standard on low-end game machines.  
Expansion of this concept into 3D is an obvious next step.  I've been
thinking idly about 3D sprites, and suspect that it wouldn't be all that
hard to do.  Z-depth is just like sprite priority, but with more bits.
That alone would give you 3D isometric sprites that could be moved in
X,Y and Z.  Perspective will require a bit more support.  But recognize
that you can probably get away with recomputing the perspective view
of the moving object only a few times a second (assuming that the
3D sprite is double-buffered) since it will blur as it moves and this
will conceal any transient effects.

     All this just gets you the ability to move a few objects around
in real time against a generally static background without having enough
computational power to redraw everything on every fram cycle.  But
you still don't have full collision detection.  A true voxel-based
collision detection system is likely to be a bit expensive for now.
But it might be possible to fake it for some common situations.

					John Nagle