Message-ID: <3341758B.38C9@ctv.es>
Date: Tue, 01 Apr 1997 22:52:27 +0200
From: Jose Manuel Lopez-Cepero <sigma AT ctv DOT es>
Reply-To: sigma AT ctv DOT es
MIME-Version: 1.0
To: Leath Muller <leathm AT solwarra DOT gbrmpa DOT gov DOT au>
CC: djgpp AT delorie DOT com
Subject: Re: Allegro 3d question/bug?
References: <199703311107 DOT VAA23606 AT solwarra DOT gbrmpa DOT gov DOT au>
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Hello!

Leath Muller wrote:
> 
> > with an FPE with the only traceback on some obscure _triangle+1055. So
> 
> fistp can be a real pain if you try to write a 32bit integer value while
> the fpu is in 64/80 bit mode. You say you have no experience programming in
> asm, so I assume this is compiled code by DJGPP - in which case I have
> no idea... DJGPP is normally very good (overly good... ;) at loading and
> storing the correct control words... if you coded the asm, make sure the
> fpu is in single precision mode, this might help (can anybody back me up
> on this? I had this problem a while ago and solved my problem by doing
> this... I think...)

It is DJGPP code; the Allegro lib, more specifically.

> > I then tracked the possible cause of the error on the drawing of
> > polygons with *very* (-8000 or so) large coordinates. Elliminating them
> > solves it, but sometimes one of these falls on the screen and then the
> > routine dies. Any help? ;)
> 
> I would suggest making sure you don't have polygons that large in your
> rendering at all: split them up... :)  And I am a little confused as to

Hey, if it was so easy... ;)

> what you mean by very large coords... are you talking world or view space?
> and if your talking view, do you mean the z value is very large? If you have
> clipped the polygons correctly to your view volume, you shouldn't have  this
> problem...

The problem is that once projected the coordinates fly up to a value
that overflows the poly routine. I think the clipping is being good done
(I placed it and it seemed to work), but the trouble is now when I get
very (*very*) close to a polygon with relatively large world
coordinates; the projection routine would map correctly the vertex that
falls into the screen, but the other ones would get to the edge.
Example: a vertex on 0,0 and others on 30,0 and 30,30, getting closer to
the first one, when z gets small then dividing by it (what project does)
is really a multiply. I have to display it because 0,0 maps on the
screen, but meanwhile the 30's on the coordinates project to larger
values, larger, larger... crash :-)

> > Another thing is profiling. I can profile it OK but the routine is
> > _very, very, very_ slow! A scene that was drawn at 36 fps with no
> > trouble now used 2 seconds for a single frame. There is a routine that
> 
> Are you using a pentium? If  you are, use the profiling registers of the
I wish I would ;)

> pentium - the code runs at the same speed, and is accurate to a cycle. If
> your using a 486, then, ummm, heh heh... ;)  I would actually suggest using
> uclock() on a 486 as this should give fairly accurate results, without
> killing performance...
I'll try to.

Many thanks

-- 
 _*                        
\ |/_|\/||\                                 sigma AT ctv DOT es      
_\|\/|  ||_\  (formerly Sigmatech)      Jerez / Cadiz / Spain