Low-level explanation of bone weight and curved bones?

I’ve tried quite a bit of googling, and I can’t seem to find any information on how exactly weight painting actually works and how weights influence vertices.

I’ve been trying to figure it out with a basic plane. If I create a plane and 1 bone, parent it to the plane (with automatic weights), when I move the bone in pose mode it brings all 4 vertices along with it in a 1:1 fashion (as I’d expect). Right now, all vertices are in the bone’s group and all weights are 1.

Now, if I assign all the vertices to only have a weight of .5, this has no impact at all on how the vertices move with the bone. they still move with the bone 1:1.

Now if I create ANOTHER bone and another bone group, and assign all my bones a weight of .5 on that one, now everything moves in a .5:1 ratio (if I move the bone 1 unit to the right, the vertices move .5 units to the right).

This effect is the same if I have both weights for both groups be 1. They still move at a .5:1 ratio.

What exactly does a weight of .5 MEAN? The only explanations I can find is that weight is “influence” but they don’t go into what that means at all.

I also can’t find ANY documentation on how curved bones actually work as well. I search “Blender Curved Bones” in Google and there’s literally no information that comes up on the first page. When I say “curved bones” I mean the option in the “Bones” dialog under “Deform”.

On an unrelated note, why when I search for anything Blender related on Google do I get docs that refer to 2.4 instead of 2.5 or 2.6? Do most people still use 2.4? I used to use Blender several years ago (but stopped around the time that 2.5 released) and trying to learn anything with the new interface is a huge headache. Is there a place that can tell me of all the name and interface changes between 2.4 and 2.6?

Search on youtube. Most tutorials are on there now.

Bone weighting hasn’t changed in a while. Older tutorials are still good, for the most part.

Bones try to move the vertices assigned to them. If there is only one bone, it won’t matter if the ‘weight’ is 1.000 or 000.1, all the verts will move with the bone. With two (or more) bones, however, Blender looks at the bone weight. If both bones have the same weight, then each will have equal influence. Again, it doesn’t matter if the weight is 0.1 or 0.5 or 1.0. If the weight is the same, the influence is balanced. Now, if one bone has weight 1.0, and the other bone has weight 0.1, then moving the first bone will drag the verts along 90% of the way, while the other bone will only drag the verts 10% of the distance (math isn’t exact, but you get my drift, I hope.)

I think the curved bones you are talking about are called spline bones. Try searching for tutorials on spine rigs or snake rigs.

The best (sometimes the only) place to find out about changes between versions is in the blender.org release notes. LOTS of invaluable information there, but it’s mostly written from a developer standpoint, so you have to wade through a lot to find the nuggets that apply from an end user point of view. Also, the notes are not cumulative, so you have to go back and read them all, in order, in case something changed and then changed again.

Rigging has been overlooked completely in the blender updates imo. I want to change the weight a certain bone has on the mesh, I have to go into object mode and select that bone then select the mesh and enter weight paint mode. I figured that out completely by accident. I assumed there would be a way to select the bone you are weight painting for, but I have yet to find out if that is even possible. Every time I try and rig a mesh I am instantly reminded why I never rig meshes or animate them with anything but shape keys.

Thanks for the answers! That makes more sense. I just wish the tutorials would go more in-depth (and I also wish that there were more NON VIDEO tutorials).

It seems silly that I have to search for “segmented b-bones” when the tool itself is labeled “Curved Bones” in Blender.

Non-Video tutorials are harder to produce than video tutorials. Well, maybe ‘harder’ is the wrong word, but they are certainly more time-consuming. And it is silly that segmented b-bones are not called curved bones in tutorials or documentation. It is really hard to learn something when the terms aren’t consistent.

Unfortunately, tutorials are pretty much a volunteer effort, so we are stuck with what ever someone is willing to produce. I, for one, would be happy if people producing video tutorials would at least write a check list for themselves before they start, so we could avoid listening to all the hemming and hawing when they can’t quite recall a setting, or forget to do something and have to go back to fix it.

Maybe I’ll rework that post and those example files into the documentation if I get some time next week. I’ve got a few things that I want to make into non-video rigging tutorials soon.