Letter to id:

I know you folks aren't doing any support/etc for those of
us writing new wads, though you did release the code for the nodes,
(which we all appreiciate a LOT...)

but I have a question about a limit we've found in the engine, and while
I could spend hours and hours hacking together test wads till I figure it
out, I thought you folks might be able to answer it quicker (even
unofficially)

We're seeing what we call HOM (hall of mirror) effects even when all the
sidedef & linedef stuff is correct for the sectors, when there are more then
X number of sectors (or possibly X number of lindefs or vertexes) in view
at once.  In other words, the stuff looks fine up close, but pull back and
when enough other stuff is also in view, the engine barfs this HOM effect
instead of working right.

I'm NOT complaining, every engine has limits (and this is one of them :)
but for those of us into building wads, any idea just how many X equals?
and is it the linedef or the sectors or what that X relates to?  We suspect
it's lines, but aren't sure.

If you don't feel you can answer (even unofficially) we understand, but
any hints even would help us make better levels.

Seth
(on behalf of all Doom wad authors...)

Subject: Re: Doom engine question (re: Engine limit - HOM effect)

Seth:

This bug is known as the "too many 2-sided lines" bug.  It is actually a  
feature now!  It was explained to us that when we see the "hall of mirrors"  
effect, we have too many 2-sided lines, which slows down the engine -- so we  
need to slap some 1-sided lines in front of the offending lines so everything  
looks a-okay and keeps the engine running smoothly for game players of all ages  
and machine speeds!

Oh so sorry,

| John Romero (romero@idsoftware.com) id Software                   |

From: scohn (Seth Cohn)
Subject: Re: Doom engine question (re: Engine limit - HOM effect)
To: johnc@idcube.idsoftware.com (John Carmack)
Date: Thu, 7 Apr 1994 23:38:14 -0600 (MDT)
> 
> What a coincidence!  Sandy was just complaining about this in regards  
> to one of his levels.

Tell Sandy great minds code levels alike. :)

> 
> My response was:  if it shows up, you have too many two sided lines.   
> This was not a very good response.

John Romero said the same thing.  I accept that answer, but wonder just
what X equals?  how many 2 sided lines?

> 
> We have to try to keep our levels playable on a broad range of  
> machines, but people doing homenbrew levels should be able to make  
> more complex designs.  I don't know exactly what the problem is -- I  
> have bounding checks on all the size limited arrays I know of (causes  
> a program abort with an error message).  I am probably going to look  
> into it over the weekend.
I built a 12x12 grid (checkboard style) and played with it, and it showed
up on grids of lesser size also.  If it'll help you, the wad is on ocf.unt.edu
(the doom ftp site) called gridwad.zip

The number is rather small, under 200 for sure.

> 
> Were you in an area with sky ceilings?  The sky was a hack into the  
> engine, and may be related to the problem.

No sky ceilings. Happens with any texture.  (BTW, considering that I heard
you hacked ceilings into Blake Stone also, you must be related to Michaelanglo.)


> 
> If I fix it, it should make 1.3, which has been sitting here for  
> weeks waiting for sound code fixes from the sound driver guy...

COOL! If I can do anything to help, be glad too.

Seth


