Telling sectors apart once they're joined

[Duvo]

Hi guys, I have an issue I can't solve for the life of me. I have a script that identifies sectors by id and then compares their geometry, but I found out the hard way that if a person decides to join two sectors together in doom builder, you can have two sectors under 1 index, with separate characteristics. What I'd like to know is, once you join two sectors together, is there still a way to get them by some kind of reference?

[phantombeta]

They're not actually two sectors under one index, merging sectors in Doom Builder makes a single sector made up of two separate shapes. There's no built-in way to easily tell these separate shapes apart inside GZDoom.

[fakemai]

I'm not clear what the purpose of the script is. The two shapes are one sector, what one does the other does, and you can't break it apart in-game. If you were trying to do something like an area calculation it might be possible to figure out the individual shapes from the sector struct since it knows what lines (and then vertexes and sidedefs) are associated with it, but I expect some map design tricks or plain malformed maps may disallow this.

[Duvo]

It's an edge walking algorithm. Normally i could walk the outer hulk of the sector and then walk the inner holes separately and I'd know that the inner ones were holes because there would still be vertices to track once i arrived at the start, but if two outer hulls are separate it will count the second outer sector area as a hole in error. It's a puty there isn't, but that's a limitation of wads themselves i suppose. I will try something else

[phantombeta]

You can find the sector shapes by walking the lines, you just need to determine which polygons are within which afterwards- one polygon inside the other is a hole, polygons at 0 depth are separate shapes.

Polygons can be nested deeper than one level deep, in which case, even depths are actually fully separate shapes and should be hoisted up to depth 0. Then these shapes should themselves be checked for any shapes that need to be hoisted up too.

The only issue with this is that a lot of early Doom maps are malformed. More modern ones tend to be fine, but older ones often have unclosed sectors, even the IWAD maps. Some of these are mistakes where a line was made that added an extra vertex instead of actually closing the shape, but some are indeed missing whole lines needed to close the shape.

[fakemai]

I think older versions of doom2.wad had an unclosed sector in Courtyard, the one with the cell pack, but even the more recent ones have that door that has two-sided lines on the side walls into void space. Anyway it shouldn't be too hard to determine if a shape is unclosed at least, and you can filter out lines that are internal just by checking if both sidedefs point to the sector. Attached an example of some slightly unusual sectors arrangements, all of the sectors use a unique flat and the marble one is part of a closed room outside, but an even better trial for what you're doing would probably be something like 10 Sectors or any other mapset that has to work to such strict limitations.

[Duvo]

You can find the sector shapes by walking the lines, you just need to determine which polygons are within which afterwards- one polygon inside the other is a hole, polygons at 0 depth are separate shapes.

Polygons can be nested deeper than one level deep, in which case, even depths are actually fully separate shapes and should be hoisted up to depth 0. Then these shapes should themselves be checked for any shapes that need to be hoisted up too.

The only issue with this is that a lot of early Doom maps are malformed. More modern ones tend to be fine, but older ones often have unclosed sectors, even the IWAD maps. Some of these are mistakes where a line was made that added an extra vertex instead of actually closing the shape, but some are indeed missing whole lines needed to close the shape.

I was afraid of that.. I had already considered that a map could have irregular geometry, especially if it was edited with a text editor. In the future I may include a cleanup script or at least an audit.

After mulling about my problem for the weekend I think I might have a solution. I could run a constrained Delaunay triangulation algorithm on the map, sector to sector. Then, I flood fill each area to make my subcomponents. After that it's a matter of drawing a border strictly around those shapes and then using a handful of formulas to find out what shapes exist in others. I think I'll still have trouble identifying holes when sectors with the same ids overlap multiple times but it's the best I've got right now