http://www.celephais.net/board/view_thread.php?id=4&start=4469&end=4469
highly useful hack 

hmm, on a second thought i always used
"use" "trigger_once"
"touch" "SUB_Null"
probably just another way (without apparent downsides). 

Thanks for the speedy reply, I'll get on to it. 

Great stuff! 

Surely logic gates are a better choice than creating a new progs.dat for this one thing.

But I am curious to know if there is a simply one-entity hack to do this; that would be useful. 

I must have had this page open for like an hour before commenting :P 

...I can open a .qc file, fiddle with it and recompile in less time than it takes me to build brushwork. My editor compile GUI can then re-run the map in one click with -onlyents selected to run the map with the new progs.dat in about three seconds. So, apart from the fact that I'm not too good with QC, I would find it easier.

My map will have to have my progs.dat to play as it has a mixture of monsters, so again, it is easier for me.

But I am not a 'wheel inventor' so the notnull thing suits me fine.

Having no professional interests in gaming, programming, IT, web-design etc, all of this mapping lark is just a bit of fun that takes an hour or so of my time every other day when I'm at home. And I enjoy poking around in Quake's inards even if I get lost every now and then:-) 

FrikaC posted a killable Chthon on I3D:

http://forums.inside3d.com/viewtopic.php?t=475 

Ok, this DOES work. He's how to make an invisible barrier that stops monsters but not players. This only works for monsters that don't swim or fly, and if the monster jumps or is pushed, they may pass the barrier.

First build a 32unit high step where you want the barrier to be. Apply a regular solid texture to the brushes. Now make a clone of this brush and position it above the existing brush. Make it 64 units high - it can actually be as high as you like, but lets use 64 units for now. Apply the clip texture to this. Select both brushes and make them into a func_wall entity. Now move the whole thing down into the floor slightly so that the solid brushes are 16 units below the floor (if this doesn't work, try 8).

Compile the map and run it in Quake... hey presto! The monsters should be stuck behind the barrier. Hopefully, you should be able to walk through the barrier without problems.

Turns out I used this weird trick in apsp1 after all. It was reused twice in dm3rmx when I rediscovered how it was done, though I killed the barriers in that to allow the monsters to pass after a certain time. 

Here is an example map of stupid test things which happens to also contain the trick I mentioned in the above post: http://than.leveldesign.org/files/invisBarrier.7z

Ignore all the stupid shit I put in there, and just watch how the enforcer won't come out of his little box. Try the same thing with a fiend... you'll be in for a shock. 

You are simply a one-man repository of l33tness. This'll come in big use with my base map =D 

A trick I use is even simpler -- players can cross any gap in the floor that is 32 units or less across, becuase they have a 32x32 bounding box and use hull1 to do their collision.

Monsters, on the other hand, use hull1 or hull2 for collision, BUT they use hull0 to do their pathfinding. Since there's a gap in hull0, they think they can't cross it. So just like cattle guards at the entrances to pastures, you can simply put grates or other gaps where you want the monsters to be blocked.

Gratuitous cattle guard picture: http://www.3rf.org/album/ComancheSprings/slides/cattle%20guard.jpg

And an example in antediluvian: http://www.celephais.net/shite/ant2.jpg 

That's pretty nifty. They will come at you one the floor is "filled" like with a func_door, right? 

http://forums.inside3d.com/viewtopic.php?t=475

FrikaC explains how to make a Chthon that can be killed by the players weapons rather than electrodes, without doing any qc coding or using another progs.dat 

very well written, too. Helped me understand certain aspects of the coding process more intimately (though we're still 'just friends' at this point).
But since I can't test it, I'd like to clarify one thing... he won't pop out and start going? almost immediately after starting the map he'll begin tossing his loud fireballs around? or am I confused? 

is there a way to make a monster invulnerable until a certain point, at which he'll become vulnerable to weapons/lighting/smooshing? 

this is possible. simply add a "invincible_finished" "#" field.
the awkward thing is that the # seconds start counting down when the map starts, so events involving such monsters have to be carefully planned. 

i hear that FrikaC has a way to make a killable Chton without quake-c? or was it marcus sklar. . . 

you're thinking of that level from 1997, called "THEFLY" or something... I think it was by this guy Marcus Klar... 

no way to trigger it huh? that takes alot of the fun out of it... 

I know this is probably getting annoying, but how do you get monsters to drop weapons/ammo? when making a floating weapon, do you simply place it on a func_wall and then kill it upon starting the map? Any other "widely known" hacks? 

as far as i know, you trigger this cthon the normal way. I'd have to re-read the tutorial to be sure, though.

And yes, you kill the func_wall immediately after map load, using a trigger on the start point or something. At least that's the traditional way to do it. I wonder if this would work instead:

"classname" "func_wall"
"nextthink" "0.1"
"think" "sub_remove"

or would that not work because func_walls already have a think function? 

A func_wall has no think function, so that would almost work as it stands. The problem is that the items will not have been dropped to the floor by 0.1 seconds in, so you'd remove the func_wall too soon. Setting nextthink to 0.5 would be safe(items drop at 0.2 seconds in), and probably won't be seen by the player anyway. 

Cool, so that would work.

I much prefer a clean hack to a messy hack. 

...hiya, I'm at the stage where the only thing left to do in this map before release is to enable a switchable ambient sound (ambient_drone). Is this doable via an info_notnull hack? It only needs to go from 'on' to 'off' once. I can't really afford to use brush entities as I'm a bee's thingy from the markedgesurfaces vanilla limit.

Thanks in advance.