GZDoom Builder linedefs that trigger W1 from front side only?

I seem to be having some trouble that I've never run into before. I have a couple linedefs that trigger some traps, and I want them to trigger on the return from hitting a switch. So you walk through the area, hit the switch, then as you're walking back boom a trap opens, everything works fine except the trap triggers as soon as you walk over the linedef (even from the back side). I've tried flipping the linedef and same result. I figured maybe it's some bug specific to the W1 floor lower action I'm using, but it happens in another part of my map where the floor raises.


How do I make sure a linedef will only trigger when I walk over it from the FRONT side? I assumed that was default behavior in Doom.

All walkover-activated linedefs work the same way when walked over from either side, with the only exception being teleporter linedefs, which work from front side only. Also, all switch-activated linedefs work from the front side only.

If you want a certain action to trigger only after another action has been triggered, you have to exploit the behavior of the specific actions. For example, set your linedef action to "WR Floor Lower To Highest Floor" and make the target sector neighbor with another sector with a floor of the same height, so that the target sector will not move at all when the linedef is triggered - however, the other sector will be affected by another linedef with action "Floor Lower To Lowest Floor" placed in another part of the map, making the other sector's floor lower, and therefore, after the player returns to the first linedef and trigger it again, the original target sector will move as well this time, because now its highest neighboring floor will be lower.

If it's a map for a format and port that supports scripting, you could do it in a script. e.g. when the switch is flicked it runs a script that does what you want the switch to do and also activates the trap line.

Or a voodoo doll if it's for Boom compatible.

boris said:

Or a voodoo doll if it's for Boom compatible.

How would that enforce 'front side only'? The script is needed to do a 'if (lineside() == 0) check, not to chain actions.

If it's UDMF, you have a flag for it in the linedef properties.

Graf Zahl said:

How would that enforce 'front side only'? The script is needed to do a 'if (lineside() == 0) check, not to chain actions.

Of course that doesn't enforce "front side only", but if the goal is to have the monster closets open after the switch is pressed it would work ok. It's just another option to work around shortcomings/quirks of the engine...

scifista42 said:

All walkover-activated linedefs work the same way when walked over from either side, with the only exception being teleporter linedefs, which work from front side only. Also, all switch-activated linedefs work from the front side only.

If you want a certain action to trigger only after another action has been triggered, you have to exploit the behavior of the specific actions. For example, set your linedef action to "WR Floor Lower To Highest Floor" and make the target sector neighbor with another sector with a floor of the same height, so that the target sector will not move at all when the linedef is triggered - however, the other sector will be affected by another linedef with action "Floor Lower To Lowest Floor" placed in another part of the map, making the other sector's floor lower, and therefore, after the player returns to the first linedef and trigger it again, the original target sector will move as well this time, because now its highest neighboring floor will be lower.

Ah thank you. I guess that's what people meant when they told me mapping for doom required some real out of the box thinking.