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Turn off Merge Geometry completely?

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I'm currently building a vanilla Doom map and trying to create a tunnel, using two sectors on top of each other. I know this is possible, but every time it tries to merge the geometry. The "Merge Dragged Vertices Only" option already helps a bit to accomplish this, but is there a way to completely turn off merge geometry? I can't find any option for this. I'm using the latest UDB, ver. R3346 (64-bit).

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Sorry, it's not actually possible as you appear to believe. Even if you do disable merging completely on the editor, stacking sectors is not something vanilla Doom can actually do, only one floor and ceiling can exist in any one point in the world physically. 

 

You might be confusing the engine with Build (Duke3d, Shadow Warrior, Blood), where two sectors could occupy the same space but which one you interracted with depended on where you came from. Doom doesn't have this, as maps are compiled to use a BSP and the sectors are simply reference information from the lines that build them. Where you are placed is where the BSP can find you, and only one sector can ever be at that location.

 

You may be wondering what happens if two sectors appear to overlap, then. The simple answer to that is nothing good. The BSP lookup will still only find one sector, which ever one that'll be will be based entirely on happenstance, it won't produce anything coherent. 

Edited by Edward850

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21 minutes ago, Edward850 said:

Sorry, it's not actually possible as you appear to believe. Even if you do disable merging completely on the editor, stacking sectors is not something vanilla Doom can actually do, only one floor and ceiling can exist in any one point in the world physically. 

 

You might be confusing the engine with Build (Duke3d, Shadow Warrior, Blood), where two sectors could occupy the same space but which one you interracted with depended on where you came from. Doom doesn't have this, as maps are compiled to use a BSP and the sectors are simply reference information from the lines that build them. Where you are placed is where the BSP can find you, and only one sector can ever be at that location.

 

You may be wondering what happens if two sectors appear to overlap, then. The simple answer to that is nothing good. The BSP lookup will still only find one sector, which ever one that'll be will be based entirely on happenstance, it won't produce anything coherent. 

Thanks for clarifying, makes sense.

 

Back in the days I thought I was able to do this. Well, sort of... As long I couldn't see both sectors at once, or it would glitch.

But then again, I was using DEU without any Node builder. Had no idea I had to use something like idBSP and had many glitches in my map. So I guess it was never meant to work that way.

 

And indeed, I saw that it was possible in Duke3D, so I tried this in DEU as well. ;)

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If you want a vanilla compatible engine that can do something like it, you could investigate Eternity which has interactive wall and plane portals, and you sort of make your map in layers to stack everything. 

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Back in the days, there was RORDoom which allowed this kind of things to be done. It's also something that works in the Build engine games, as well as in other portal-based engines like Dark Forces. Basically the way a portal engine works is that it renders one sector, starting with the sector the viewpoint is in, then recursively go through the two-sided lines to draw the sectors on the other side, and so on. It allows to cheat with geometry (because you can tell it the other side of the line is actually a detached sector) to make non-euclidian areas, but it suffers from much worse performances than a BSP-based engine.

 

Nowadays, some source ports (such as the mentioned Eternity, and also EDGE and GZDoom) allow to explicitly define portals.

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Several vanilla tricks (most notably Iikka's) required unmerged vertices, maybe that's what you're remembering..?

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4 hours ago, Mordeth said:

Several vanilla tricks (most notably Iikka's) required unmerged vertices, maybe that's what you're remembering..?

Yes, I remember doing something like that. It worked, as long I wasn't able to see both sectors at the same time.

When I saw them both I was getting the mirror effect.

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