Fake Bridge Problem

I've seen them done in several wads before... those bridges that have a "step" texture on their sides and many lines that go through it. These bridges could go down and up instantly.

Today I finally had a situation that actually called for one. The level's scenario is a large lava pit with various buildings and such. I thought such bridges would be the best idea. And now I finally get how to do them, without the tutorial (so I thought): One sector, floor -128 (the lava), with STEPTOP as main textures (as it happened, this is sector 37). Another sector inside, floor 0, thats lines refrence itself both front and back (sector 38). This sector has another part in void space, connected to two dummy sectors: one with a ceiling of -128, the other with a floor of 0. To make the platform go down, you use floor up to lowest ceiling; to go up you use down to highest floor.

This is exactly what I did. Whenever you walk over the "down" lines, everything's fine. But when you walk over the "up" lines, something weird happens. The inner part goes down, as if you'd walked over the down line, while the outer part stays up. So you have basically the perimiter of the bridge walkable, but once you go in the center you fall and can't get out.

I also know that the inner area was originally ok, because I tried first without any floor movement tags, and I could walk on the whole bridge. I assume the trouble starts when you walk over the "up" lines, but that doesn't make much sense, because the center instantly goes down to the lava.

The most puzzling part is, after walking over the "up" line, the dummy sector area is fine. IT is at a floor height of 0, whereas the other part of sector 38 has a floor of -128... which also doesn't make sense.

I looked at the only wad I could remember clearly having such a bridge, that I have: Community Chest. There, everything was roughly like I had it. What could be wrong?

Looks like your self-referencing linedefs are too far apart.

As a rule of thumb, the gap between the linedefs that make up the self-referencing sector must not be 64 units or more, as the player will fall off them if they are. (as they're just linedefs, like tightropes really)

Also, don't use Zennode as it doesn't like these bridges and you'll fall off the linedefs regardless of how close they are together. Community Chest was built with DeepBSP for this very reason and Zennode was only used for the reject data.

(If you look at the first map of CC, you'll notice that the 128x128 bridges that go across the octagonal sewer in 4 places have 2 groups of linedefs rather than 1. This was because having just one group of linedefs going round the outside caused the player to fall into the middle of the bridge. So I put 2 rectangles in rather than 1 big square)

Oh, I see. So it's supposed to do that. Is there a minimum? Meh, I'll just figure it out. Thanks again.

No minimum, but I normally use a gap of 48 units. (which is probably about the best)

I've found that you tend to fall through 48-unit gaps if you turn sideways.

But, I did fix it... I copied a trick you used in that CChest level (I think you made level 1): two self-refrencing areas. This also allowed me to make the bridge bigger. :-P

The two linedefs of the invisible bridge platform should be close together, because it's exactly these linedefs you're standing on and not on the actual sector. So in order to prevent the player from 'falling through', the spacing between the two outer linedefs ought to be less than 40 units.