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<H1>[MUD-Dev] Re: How to represent a 3d object...</H1>
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<LI><em>To</em>: <A HREF="mailto:mud-dev#kanga,nu">mud-dev#kanga,nu</A></LI>
<LI><em>Subject</em>: [MUD-Dev] Re: How to represent a 3d object...</LI>
<LI><em>From</em>: Oliver Jowett <<A HREF="mailto:oliver#jowett,manawatu.planet.co.nz">oliver#jowett,manawatu.planet.co.nz</A>></LI>
<LI><em>Date</em>: Sat, 25 Apr 1998 18:20:42 +1200 (NZST)</LI>
<LI><em>Delivery-date</em>: Tue Apr 24 17:48:07 1998</LI>
<LI><em>Delivery-date</em>: Tue, 24 Apr 1998 17:48:07 -0700</LI>
<LI><em>Envelope-to</em>: claw#kanga,nu</LI>
<LI><em>Reply-To</em>: <A HREF="mailto:mud-dev#kanga,nu">mud-dev#kanga,nu</A></LI>
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<PRE>
On Fri, 24 Apr 1998, Ben Greear wrote:
> I am thinking about how to represent a 3d object in a 3d world.
[...]
> I envision the object as a collections of intersections (nodes) and faces.
> The two big questions are: what kind of data structure should I use for
> in-memory storage, and how to encode this for storage in a persistant
> storage mechanism.
> There must be some standard way of representing this on disk, does anyone
> have any pointers??
A few comments on in-memory formats (be warned, I last looked at this
about 3 years ago):
You can represent the object as a list of vertex locations (nodes), with
the faces being defined as a list of vertex references in some particular
order around the face (so the normal is well-defined). Normally (no pun
intended) you'd precompute the normals of each face to speed things up.
Having the normal ready can help with hidden-face removal, and also speeds
up various shading models if you feel so inclined.
Store the object untransformed, with location/orientation/scale/etc info
separate. It's likely that you'll be changing these parameters frequently
(otherwise: why not just use a static bitmap?) and roundoff errors are a
real killer, unless you really want the Incredible Shrinking Object. This
also makes having multiple instances of a model in different locations
easy.
You'll probably want some sort of bounding box information if the object
is part of a larger world - x/y/z extent information may well be enough if
you don't have obscurely-shaped objects. Very useful for optimizing
display, and for collision detection etc.
There's a large amount of information available on ways to display 3d
objects, which affects how you want to store the data internally -
IIRC the comp.graphics (.algorithms?) FAQ has good references to this
type of thing.
A search dug up <URL:<A HREF="http://www.dcs.ed.ac.uk/~mxr/gfx/3d-hi.html">http://www.dcs.ed.ac.uk/~mxr/gfx/3d-hi.html</A>> which
has quite a list of 3d storage formats. You may want to look at one of the
binary object formats for DB storage - OFF seems promising from a quick
glance through. 3d formats tend to like representing complete scenes made
up of lots of objects with huge piles of surface information, so your main
problem may be finding a simple format :)
Question: what environment is this aimed at? Some way to visualise a
particular object (and/or manipulate it) - ie. you're only displaying the
object itself? Hm, this could be a relatively cheap addon to an otherwise
non-3d system - a nice way to visualise and interact with objects carried,
etc.
"Interesting, a strange metallic sphere with three buttons in a triangle
on the top. I wonder what happens if I push the red one. <click> .. I
don't think the way it started flashing is a good thi--"
<boom>
Or are you aiming at displaying an object within a larger 3d world also
containing other objects / walls / avatars / etc?
-O
--
MUD-Dev: Advancing an unrealised future.
</PRE>
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<li><strong><A NAME="00726" HREF="msg00726.html">[MUD-Dev] Re: How to represent a 3d object...</A></strong>
<ul compact><li><em>From:</em> Ben Greear <greear#cyberhighway,net></li></ul>
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<LI><STRONG><A NAME="00654" HREF="msg00654.html">[MUD-Dev] How to represent a 3d object...</A></STRONG>
<UL><LI><EM>From:</EM> Ben Greear <greear#cyberhighway,net></LI></UL></LI>
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<ul><li>Thread context:
<BLOCKQUOTE><UL>
<LI><STRONG>[MUD-Dev] Motivations (was something else...)</STRONG>, <EM>(continued)</EM>
<ul compact>
<ul compact>
<LI><strong><A NAME="00401" HREF="msg00401.html">[MUD-Dev] Motivations (was something else...)</A></strong>,
s001gmu <a href="mailto:s001gmu#nova,wright.edu">s001gmu#nova,wright.edu</a>, Tue 05 May 1998, 15:55 GMT
<UL>
<LI><strong><A NAME="00403" HREF="msg00403.html">[MUD-Dev] Re: Motivations (was something else...)</A></strong>,
Richard Woolcock <a href="mailto:KaVir#dial,pipex.com">KaVir#dial,pipex.com</a>, Tue 05 May 1998, 16:39 GMT
</LI>
</UL>
</LI>
</ul>
<LI><strong><A NAME="00358" HREF="msg00358.html">[MUD-Dev] Re: (fwd) AD: [custom graphical] whitestar Crossfire MUD</A></strong>,
Jay Sax <a href="mailto:cimri1#gte,net">cimri1#gte,net</a>, Mon 04 May 1998, 10:16 GMT
</LI>
</ul>
</LI>
<LI><strong><A NAME="00654" HREF="msg00654.html">[MUD-Dev] How to represent a 3d object...</A></strong>,
Ben Greear <a href="mailto:greear#cyberhighway,net">greear#cyberhighway,net</a>, Sat 25 Apr 1998, 02:44 GMT
<UL>
<LI><strong><A NAME="00675" HREF="msg00675.html">[MUD-Dev] Re: How to represent a 3d object...</A></strong>,
Oliver Jowett <a href="mailto:oliver#jowett,manawatu.planet.co.nz">oliver#jowett,manawatu.planet.co.nz</a>, Sat 25 Apr 1998, 00:48 GMT
<UL>
<LI><strong><A NAME="00726" HREF="msg00726.html">[MUD-Dev] Re: How to represent a 3d object...</A></strong>,
Ben Greear <a href="mailto:greear#cyberhighway,net">greear#cyberhighway,net</a>, Sun 26 Apr 1998, 04:14 GMT
</LI>
</UL>
</LI>
<LI><strong><A NAME="00242" HREF="msg00242.html">[MUD-Dev] Re: How to represent a 3d object...</A></strong>,
J C Lawrence <a href="mailto:claw#under,engr.sgi.com">claw#under,engr.sgi.com</a>, Wed 29 Apr 1998, 22:49 GMT
</LI>
</UL>
</LI>
<LI><strong><A NAME="00663" HREF="msg00663.html">[MUD-Dev] Re: MAPPING: Creating a bitmaped graphic from map</A></strong>,
John Bertoglio <a href="mailto:alexb#internetcds,com">alexb#internetcds,com</a>, Sat 25 Apr 1998, 01:20 GMT
<LI><strong><A NAME="00620" HREF="msg00620.html">[MUD-Dev] (fwd) AD: [custom graphical] whitestar Crossfire MUD</A></strong>,
J C Lawrence <a href="mailto:claw#under,engr.sgi.com">claw#under,engr.sgi.com</a>, Fri 24 Apr 1998, 18:29 GMT
</LI>
</UL></BLOCKQUOTE>
</ul>
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