[Vanilla] Instantly lowering ceilings!

[Obsidian]

This is a little trick I discovered some time back that involves door functions. First, the example wad:

 

TryMe.zip

 

It works pretty reliably in the source ports I've tried it in (Chocolate Doom, PrBoom+ and ZDoom) and is surprisingly simple. The easiest explanation can be found in the DoomWiki article for doors:

 

Quote

"A closed door is constructed as a sector whose ceiling and floor are both at the same height as the neighboring sectors' floors. When the door is opened, its ceiling moves up at a controlled rate to four units below the lowest adjacent ceiling. By convention, doors are 16 units thick, but any thickness will work."

 

Where the trickery comes in is the "lowest adjacent ceiling" bit: if you have a sector with a lower ceiling that is adjacent to the door sector, the door will instantly jump down to it in the same way that action 19 makes instantly rising floors. If the action used on the door indicates for it to close afterwards, it will simply play the closing sound effect and stay at the same height.

 

This works with all door specials, including ones that enemies can trigger: as you can see in the example map, the enemies can trigger action 4 and the explained setup will cause the door to instantly close. Just remember that the ceiling will always drop to 4 units below the lowest adjacent ceiling and factor that in accordingly while mapping. You can also use it in conjunction with regular doors, which can be useful if you want to construct some more complex setups.

 

Hopefully this little guide gives you something to think about: it isn't the most flashy of effects, but it can do some nifty little things within the restraints of the original Doom engine.

[Doomkid]

Awesome find!

[Juza]

25+ years later and we're still discovering functions/hacks for Doom's simplest engine. Wonderful.

[TimeOfDeath666]

This is a cool trick. I noticed it occasionally when going through /idgames when people would accidentally (I'm assuming) use GR shootable doors with a zero tag. https://www.doomworld.com/files/file/17438-the-room-below/ uses it intentionally to help transition the ceiling heights in the start room, but it's hard to tell because there are a bunch of linedefs stacked on top of each other to begin the sequence.

 

 

[Obsidian]

Ah, neat! I figured that it wasn't likely that this trick was never purposefully utilized, although at a guess I'd say that all the other really cool stuff in The Room Below might've made the usage of it get lost in the shuffle. :P

[TimeOfDeath666]

Your idea of monsters activating the instant ceilings was quite clever :)

I just remembered that instant ceilings were also used to reveal the boat when you fall into the water in the wad I posted: