The problem in the screenshot is that the skip brush is world geometry. This is what I explained above. The skip brush needs to be a brush entity, ideally func_wall (NOT func_illusionary). Alpha brush is a bad choice, because when playing the level with a port that doesn't support alpha, that brush will be fully visible. 

When world brushes touch, regardless of texture, the touching faces are removed. If top and bottom face are skip-invisible, then you can see through the sides where the brushes touch. So in order for this to work, there must be no touching (similar to the "DP" issue), for example if the skip brush is shaped like an upside down pyramid or at least has slanted sides to make sure only the floor surface matches up with the adjacent floor. However, this is problematic as well, since it may lead to the parts below or behind the skip brush to be visblocked and therefore create a visual anomaly, too. 

"Alpha brush is a bad choice, because when playing the level with a port that doesn't support alpha, that brush will be fully visible."

Didn't some just said Skip is not supported as well in some ports.. or am I blind. It seems there is couple ways to solve this problem. That I don't know what is the right way to do it anymore.

You can recommend using specific engines for your maps.. if it comes to that mentality "it should be working on every possible quake engine" you're just making your life unnecessary hard?

I just tried func_wall + alpha and it gave the best result when using Quakespasm. So if that is the wrong way to do it, then shall be it - if it works on this specific engine.. 

Do AD's fence textures not work in darkplaces? Or have I borked something somewhere? That screenshot is 100% less pink in QS.

Actually, should I care about DP at all? I only installed it tonight to see how my map would look (basically the same save for the broken plants) and experience the horror that is excessive particles and blood decals. Does anyone care if my map's broken in it? 

Sorry about that; my memory is shot!

Negke is right. Ignore my comment about exact size and retexturing, that was the actual problem I had, not the solution. The solution was a standard brush 1 unit away from grid brushes (still needing one skip brush for each gap in the grid)

I think this shows what I am meaning:-

http://imgur.com/a/PzDvZ

You can see the skip brushes in place, and the larger holes that the player could fall through, but monsters would not.

This screenshot is from the original map that was compiled and worked as intended. 

Actually, should I care about DP at all?

No. 

Like this? : https://drive.google.com/file/d/0BwxYkKdSD855amlBS1FCSWVlaHc/view?usp=sharing

Is the offsetting by 1 pixel only way to make it not hide faces from those iron bars? 

Let me get this straight. Skip is a compiler thing, so if the faces are removed does the engine port used to play the map make any difference?

Alpha does require engine support, if not supported by the engine port used to play the map the model will appear as normal and not transparent? 

Yes, that looks right. And yes, the 1 unit gap stops the grid's faces from being removed whilst allowing monsters to cross the grid.

In my map, Ogres, Death Knights and Shamblers could chase the player across the grid. 

should I care about DP at all?

It depends whether you intend to allow players to play your map without forcing them to put their engine of choice away or restrict it to some kind of elitist club. Your call but IMHO mappers shouldn't make their work dependent of one engine. 

You turn it into a func_wall so you don't need to have 1-unit gaps, because brush *entities* and world geometry don't affect each other in this regard. Yes, it's also possible to have skip-textured world brushes which then must not touch other brushes, but it's not recommended in most situations. There'll be lighting issues, too.
And you only need a single big func_wall that covers the whole space between all the bars in that area - since it's invisible to the player, there's no visible z-fighting.

Rick: Correct.
Mugwump: Correct. 

Dp got fence texture support a few weeks ago, it's only on the "development auto builds" (haven't tried myself but should work): https://icculus.org/twilight/darkplaces/download.html 

Including dosquake to my knowledge 

"And you only need a single big func_wall that covers the whole space between all the bars in that area - since it's invisible to the player, there's no visible z-fighting. "

but still this happened? Did I do it poorly?
https://drive.google.com/file/d/0BwxYkKdSD855eDdtQU1JdEpPSE0/view?usp=sharing

Though I don't remember was it func_wall or not.. have to see again.. 

Yeah, it seems to work. Thanks negke. 

So now it is come to this point I need to ask again about these keys (AD specific): _shadow, _shadowself, _dirt.

Can some one of those make this brush work as func_illusionary.. like it doesn't block lights? 

I had no idea that was what you could use func-wall for. If I ever try to map again I will have to find a use for my new-found knowledge :) 

func_wall + alpha works in Darkplaces, Fitzquake, Qrack, and Quakespasm (and probably more). That's pretty broad support.

The only thing it doesn't do is work online with protocol 15. 

After working some months on a convertion of the Doom2 Startrek Enterprise to Quake1 I discovered a file on my disk from 1997.
It's called "NCC1701D.zip" and contents a rather good impression of a Quake1 map of the Enterprise.

First I was surprised, because someone already did what I was trying in a much earlier moment.

I tried to contact the author "Andrew J. Wyllie" but my email bounced back which isn't that strange after 19 years.

I wondered if someone has heard of the name, because it's a rather good convertion. 

Hi!
This is a repeat of a post I made a long time ago on quakeworld.nu. I'm revisiting it now and someone suggested this forum to get ideas.

Basically, I'm trying to replicate the gimmick from the quake live map 'Elder' (players pick up a gold key to access part of the map), but in quakeworld.

Is it possible to do this using item_key1 / item_key2 / item_sigil ?

Has someone done this before in e.g. a duel/2v2/4v4 map? Let me know what you can! 

In your map editor, for the gold key ...

1) what flags do you have set
2) what flags are unset

And same for the door. 

Sorry, I left out the most important part of my post!
I basically know how to set up the door to open for a key etc. The problem is my keys/sigil don't seem to spawn at all in deathmatch..?

No flags set on them right now. 

Keys are probably removed by the engine for DM. Didn't see anything in the QC.

You could do like I always wanted to do, and turn the grenade launcher into a key. Just make a wall with a hole, put a shootable func_button deep down inside. Only way to trigger it? Drop a grenade in there. Label it with a texture that features a screenshot of a grenade launcher or a grenade, so players get the drift (or a message works too, I guess).

Other than that, there is a Quake 1 arena mod that I think is actively developed. I think they might code DM keys in for you. 

Rocket launcher key? Long shaft (think Star Wars). Shoot down it, and blast radius hits shootable triggers on the side(s) of the terminal chamber.