So I’m pretty new to rigging and whatnot and I’m trying to make my character’s arms bend by weight painting his forearms fully red, but for the past few days I’ve been stuck on this incredibly frustrating issue where the other half of the arm keeps getting a little paint on it and when I go to subtract it, it also ends up subtracting the forearm paint for some reason, which I have no idea as to why.
Here’s a video demonstrating said problem:
Here’s what bending the arm currently looks like with this ongoing issue:
As you see, it’s a must for me to fix this as it’s almost like the entire arm moves when trying to only move the forearm area I weight painted. I’ve looked up several tutorials and threads online but nothing really seems to be of use so far. Is there a way I can like efficiently mask out the first half of the arm and be able to only paint the forearm area I keep talking about without getting paint on the other half of the arm? I tried hiding it thinking that would work but it didn’t really make a difference and the problem persisted. Could it perhaps have to do with the arm’s topology or something? I’d truly appreciate it if someone knowledgeable on this was able to give an explanation on this silly issue as it’s currently holding back the progress on my game by a lot!
You can go into edit mode and select only the vertices you want in that group, then go to the vertex groups and add them manually, and do the same with removing them, but I’m not sure that’s going to fix your main issue.
It looks like you need a few more verts in the arm. If the video shows all your edge loops, you have one loop at the shoulder, one at the elbow, and a couple at the wrist for the cuff. You mentioned this being a game, so I assume you want to keep it pretty low poly, but adding at least one support loop above, and one support loop below the elbow will probably help you out, without adding too much geometry, and will help with the weights and bending.
I think that it looking like it’s removing weight from the forearm is just a product of how blender displays weights as a gradient from one vertex to the next. At least that’s how it behaves in my work.
For visual reference, because that helps me, this is the same cylinder, with the same rig, but the purple one has the extra loops added. Both are autoweights, with no manual fixes.
It fixed the issue of the back part of the arm being highlighted and moving when not supposed to, but the funny bending problem that makes the arm shrink seems to still continue:
I’ve fully weight painted in red the forearm area after the new loop cut on the right,
Removing weights from the upper arm bone from the lower arm should have fixed that. What do the weights look like when you click the upper arm bone? It’s also a bit hard to see what your arm is doing with the bones there. Could you switch them to stick or wire display and resend the video or link the actual file?
You don’t have elbow topology. Generally, you should use a double diamond topology on both sides of the elbow. Simple loop cuts like this don’t allow your elbow to deform correctly
If you want to try different topologies like @Joseph suggested, these are some images that came up when I googled “Low Poly elbow topology”. Maybe one of them will work better for you.
Dope, it worked. Lower arm clips a bit with the upper arm when bending it but at least it looks much better and does the job for now compared to the clips I had sent.
