CSG Failures


Hey everyone! Instead of creating a new topic every time someone finds a way to break CSG (This is not a small number of things, sadly), just post them here and they'll get looked at. Please make sure that you attach a model or rbxl file as an example (you can submit it as a confidential post if you'd like), and try not to submit the same thing multiple times (That said, we're aware of coplanar issues, please don't post hundreds of coplanar examples).

Stay on topic and don't post to criticize other's CSGs or CSG techniques. Posts with CSG tools are acceptable, as they can be helpful for us to debug CSG plugins or to others to find better/more consistent repros (And are just generally really awesome to look at in between failed CSGs).

This topic is for broken CSGs, including things such as: CSGs that work one way but not another, CSGs that can't separate, CSGs that create invisible/extra parts, etc. If it's something that should be doable but isn't, it goes here!

Unions Failing to Load
Union bug, When negating a cylinder shifts out of aliment
Union bug, When negating a cylinder shifts out of aliment

I can't finish building weapon because of CSG failure,here is image http://i.imgur.com/BI5ULht.png

Check out file of that place


I can't finish my weapon because of CSG failure

Take a look at picture and file


This plugin (EDIT: now obsolete - CSGv2 does not error) may help you. Ignore the Force CSG plugin button it adds (that’s old and I need to remove it), re-bind studio’s union shortcut to Shift+G or something (the plugin uses Ctrl+Shift+G), and it will brute force your unions for you. This plugin has helped me so much – it pretty much solves any reasonable one-stage union and it also tells you which parts couldn’t be unioned together if it can’t union the selection.


First if all,no need to be specific just look at image and see that part of CSG union is invisible.

And no i don't have any problems with other unions that's just you taking look at how messy are they.

I could not union parts at same time because of many,many and I mean many error windows.It took me hours to union parts so that it would not show error.

This is something Roblox should fix,so let them take care of it.


"First if all,no need to be specific"
Yes you do. It's your job to be as specific and helpful as possible when reporting a bug.

"This is something Roblox should fix,so let them take care of it. "
CSG isn't something ROBLOX can just flip a switch and fix. The problem is deeply rooted and it is by no means easy (if even possible) to fix. You just have to learn how CSG works and conform to it.

"I could not union parts at same time because of many,many and I mean many error windows.It took me hours to union parts so that it would not show error."
Welcome to CSG.

"And no i don't have any problems with other unions that's just you taking look at how messy are they."
Yes you do. You can't take apart this union and you've made your unions so complex and messy that you can't union them together anymore. Being someone who CSGs things like this (for reference this is the visor img1, img2, img3 and the visor you see in the first image is a single-stage union) and this, it's pretty safe to say that I know my stuff when it comes to CSGing models. Heed my advice and stick to one-stage unions, use the plugin I linked previously, and you'll be able to union your models the majority of the time, even if it does take at least some effort. If you don't believe me, send me that model but made out of parts (I couldn't take apart that one union) and I'll show you what clean CSGing is.


I'm trying to union these two pieces but I keep getting this texture glitch: The union isn't very necessary, but this seems to be happening to me a lot recently so I figured I'd tell someone.



Here's an interesting one.


You're welcome. Problem was here:

I think you two are misunderstanding what this thread is for. It's not to perfect CSG -- if they could have done that they would have done it a long time ago. It's for unions that have actual bugs with them (e.g. material/color blend problems, operation crashes / freezes studio, etc).

"The error is obvious from the .rbxm so a detailed explanation would be redundant."

How would you like it if I told you "Hey here's a bug figure out what it is for yourself." and just shoved a repro file in your face without any explanation whatsoever. You two didn't even attempt to solve the issues on your own. In your case if you had actually taken a few seconds to determine which components were the problem you would have easily recognized that you could have just reflected the model in less than a second and completed the operation successfully. You didn't even dumb the repro file down -- the issue wasn't with all of those parts -- only two pairs on the top side had issues. You should have deleted all of the ones that worked and only provided the issue parts.


The place was very obvious what was wrong. There was a missing face and several unions that couldn't separate, as well as being impossible to union those pieces normally. This is the kind of thing I was asking for, ones that we won't fix in the short term, but help us figure out what to do with CSG eventually.

"It's broken and always been that way, deal with it" is terrible logic. I do appreciate that you understand that CSG is not a simple function, but it should still work as expected! If it did, this topic wouldn't exist.

JustCSGThings This is what this topic is for. It shouldn't take that much effort to make a CSG.

Actually, what they're talking about and what you're talking about are both what this topic is for.


I often find that problems with unioning two parts happen because, in some place involving one of the parts involved in the attempted union, two different parts have faces or edges which are in the same place. Situations where Z-Fighting occurs, or even two blocks side to side such that their faces or edges are touching exactly, can cause problems with CSGs.


Correct. Coplanar objects like that are issues with a lot of CSG tools/libraries. Sadly, the only real way around it is to offset them slightly.


I find wedges have a lot of issues with CSG, I will try to get a few repro's. They seem to like me today.


Here's a strange thing. This union is not visible (even though transparency is 0), and something wierd happens when you try to negate it.

It was just a wall with a hole in it (for a door), something wierd apparently happened to it while I was doing stuff. I don't know when/why, though. :shocked:

model - http://www.roblox.com/I-BROKED-IT-item?id=266918323

(edit) and, nothing happens when you try to seperate it.


Zeekers, do you still have the components for that (i.e. ctrl+z back a bit to get the components)? I think if you're getting that error then the ChildData is corrupted.


It happened a while ago ; I definitely can't ctrl-z and undo it now.


How long ago? I remember I had issues with that when CSG came out, but I haven't had any issues with it recently.


Pretty much this.


This one seems like a bit of a doozy. My buddy IceTaurus actually found this one and showed it to Khanovich at RDC East. As he is not currently a member of the dev forum I'll post it here for him.

In his words:

I myself have run into this issue as well when trying to texture a union. There's a simple repro place attached and it can also be seen at this place where the same is happening to a completely different union (that has a decal on every face to make it darker).

Unions show as 'neon' material

Well, I don't think that's actually an issue with our CSG tool, but that is indeed a bug! Thanks for the find.