Stupid little problem with transparent textures

[Creaphis]

Every time I try to make transparent textures (ie. bars in windows) the texture seems to bleed through the ceiling or floor flats and be visible where it shouldn't be, like a slime trail. It's hard to explain, but here: see for yourself.

http://www.zshare.net/download/34314200ecb610/
(small test level)

This is really bothering me, because I've already *successfully* done this a few times in a level I'm making, and when I copy that process directly, it doesn't work anymore. Can someone open up that level in DB and tell me just what is wrong with it?

[Graf Zahl]

There's nothing wrong with the level, just with the textures. The Doom engine doesn't clip mid textures to floor and ceiling.

You have 4 options:

1. Have a small difference of light level between front and back of the line
2. Have a small difference (1 map unit) of height between front and back of the line
3. Change the textures so that they don't exceed the sector's space.
4. Use a source port that allows clipping of mid textures (AFAIK ZDoom is the only software renderer at the moment that can do it.)

[Da Spadger]

If you're using zdoom and you have a MAPINFO lump, put the flag "clipmidtextures" (No quote marks) where appropriate.

[Creaphis]

Thanks! The reason that the textures didn't clip in my earlier map is because I did have a small light difference for decoration. I never would have expected that to be the solution.

[jval]

Yes, this problem in original doom code is located in R_FindPlane() function witch merge planes depending on height, picnum and lighlevel. If you don't use a port that removes this limit a different lightlevel, a different flat picture or a height difference solves the problem.

[Maes]

There's also the long, tedious way of sandwiching each offending linedef between two padding sectors, you can see this technique in Ode to Ressurection and Elegy for Them Vigil, to make fences with bars starting from the ceiling.

There is of course the even cheaper way of setting the height of your texture to be exactly like the space you want to fill, and draw freely whatever you want. The drawback is you can't exceed 128 pixels of height with this method.

[andrewj]

jval said:

Yes, this problem in original doom code is located in R_FindPlane() function witch merge planes depending on height, picnum and lighlevel. If you don't use a port that removes this limit a different lightlevel, a different flat picture or a height difference solves the problem.

This is definitely not a "problem" or a "limit", it is an optimisation, and one that has been (ab)used to make many cool effects like fake 3D bridges, deep water and force fields.