skin modifier - skin weights keep changing randomly

[ldotchopz7FPNL]

I am trying to skin a frog character that has been rigged with CAT, problem is random patches of weight keep appearing all over the body. I keep setting them to 0, continue with my work but then later on somehow random patches appear, weighting parts to other parts, i'm pulling my hair out because of this back and forth. some parts just keep reseting, This is problem that's been around for a while but i'm only noticing it properly now, anyone had any similar experiences?

[Diffus3d]

As you adjust envelopes, smoothing, or absolute effect of verts it moves weights around.  Instead of setting them to 0, right click on the value to remove them from consideration.  

Best Regards, 

[ldotchopz7FPNL]

Sorry, i'm a little confused by what you're saying, why does it do this when set the vetex weight to 0? shouldn't they stay at 0?

Is my CAT animation moving the weights around? I need that animation to check the skinning is correct.

I am also not sure of what value you mean to right click to remove them from consideration?

Thanks

[Diffus3d]

A vert that has a weight value to it (even 0) will not be ignored for strength and falloff effects for the selected bone, depending on your usage.  It depends on how you are doing your skinning.  Are you painting the weights, using envelopes, etc?  Using absolute effect with edge loops?  Are you using BonesPro?   How you use the tool does have an effect on how that tool functions which takes some getting used to.  

In the skin modifier, instead of typing 0 you can right click on the up and down arrows (Abs. Effect) to clear out any value entries for a specific vert.  Once you do that, adjusting falloffs or envelopes for that bone will not have an effect unless maybe you are smoothing nearby into it.  At least, that's how I use it.  

The CAT rig likely has nothing to do with it.  The skin modifier is what would cause this problem unless you're going down the stack and making changes to your model, which would reorder all the verts and mess things up like this. 

Hard to say what exactly is happening but there's little chance that a weight distribution is random.  It's always related to something we've done, even inadvertently and we've all done it.  In your case we don't have that exact information so my guess is that while you are painting weights you're painting through the model without realizing it or selecting verts for 'absolute affect' adjustments accidentally and move weights to verts that were selected from behind the model.  It happens.  Backface cull vertices can help to protect from that sort of thing (but doesn't always), and maybe backface cull as a object property would help too.  

EDIT: Wording in the first sentence was bad.

Best Regards,  

[ldotchopz7FPNL]

I am actually not using the paint weights much at all, i am selecting the verts and using the Weight Tool to zero stuff out bone by bone to make sure nothing is left on other bones, but for some reason the same thing keep happening, all the toes seem to have a patch of weight on the arm, everytime I zero them out and ttheyre gone, it’s working, then something happens and they reappear again. The arm also seems to reset its weight. I do have a couple of CAT layers and i think it happens when switching between them but I don’t know why, I am not going down the stack, There’s nothings that changing with the model. But one thing is for sure, it’s the same areas coming back. I may try to recreate it in another file 

[Diffus3d]

I see.  Hmmm.   Are you skinning in play mode or setup mode?   (Red stop icon or green play icon?)

Best Regards,

[ldotchopz7FPNL]

Hi, sorry for the late reply. I have a video recording of me trying to remove weights and them reappearing again, maybe you can tell me if something i'm doing is wrong.

Apologies for the longish video. For the first 1:50 seconds you can see i am going through bone by bone using the weight tool to remove a random patch of weighting that appears, shortly after, i begin painting the some weights for the bone i am trying to work with. After that at 2:35 when i move the arm you can see the area is being affected by something, when i go into the weights again the random patches have all reappeared.

It's a very tough one to troubleshoot and i'm going a bit mad having to go back and forth, it's not working at all and making skinning impossible.

https://www.dropbox.com/scl/fi/9ga2y3hnryy4cfq1d2d6i/2024-03-20-22-01-06.mp4?rlkey=at6g5in8pbxlkn0ov... 

In answer to your question, I don't belive it's CAT anymore, I have tried in both modes and I still get weird things happening.

[Diffus3d · Accepted solution]

Interesting. I was definitely wrong about my assumptions before. My bad.  I don't personally use that weight tool for anything (I use the spreadsheet) but I can see the issue happening in your video.  It's not clear though just how blue those verts are.    

When you select one of the blue verts, what is the weight value on it in Abs. Effect?  If it's very low, like .008, why not just use the "Remove Zero Limit" and "Remove Zero Weights"?  (Removing 0 weights is similar to manually right clicking Abs. Effect.)  It would save you a bunch of time that way.  Setting the limit to a low value and clicking the button will automatically do what you're doing in this video for all the bones and verts in the model.  Save first, of course, because it takes some trial and error to find the sweet spot.  

Or, instead of clicking on the 0 value in the weight paint tool to remove the weight, can you try right clicking on the Abs. Effect button?  (Found on the "Weight Properties" rollout.  If you do that instead setting the values to 0, does the problem go away?  (Again, a weight of 0 and a weight of N/A aren't quite the same thing.  You may have luck with it.)  

Another thing you can do is use the Bone Affect Limit to prevent bones from affecting verts far away from themselves.  I use 4 for video games, and 6-8 for high end models.  The default of 20 is overkill imho.  Setting that may also solve your problem without you having to go through what I can only assume is a tedious process for every bone and vert. 

But one thing we can both agree on is that verts you zero'd out are turning blue again.  I am now a believer.  

Best Regards,

[ldotchopz7FPNL]

I think your suggestion of Remove Zero Weights under Advanced Paramaters has bloody done it! Not only has it stopped the weird patches coming back, but the model was incredible laggy when it came to painting weights, this has completely gone too. Thanks so much for that solution! 

Perhaps this is something i should do before i get going on any model. Good to know!

Thanks!

[Diffus3d]

Nice!  That is great news!  

I was recently working with a rigged model that someone sent me and the fps went way up when I removed the 0 weights!  It's so handy.  Also works wonders on game models for Unity or w/e.  

Thanks for the follow up, and I'm glad that it worked out for you.  I still don't know what caused that, but I have filed it mentally.  Best of luck on the project!

Best Regards,