Why not make Top and Bottom bones as handles for bendy bone?

Question

So I'm having trouble understanding why we need to create additional bone_in and bone_out as handles for b-bone, why not just use Top and Bottom controls? Rewatched some vids but couldn't quite understand what would be wrong with this method

I'd assumed it had something to do with relations: e.g. the rig breaks if you have the same bone act both as a target for Stretch To constraint and a handle for b-bone, or something like that. But then I:

reparented (connected) bone_def to Bottom
selected Top as Tangent handle type for bone_def
deleted bone_in & bone_out from the rig entirely
did some repositioning and rotating to have all axes pointing in the same direction cause it looked a bit ugly

Then I tried to test the it and it stretched in ways that I'd expect it to. Maybe something else had broken because of it but I just don't see it?

Answer 1 · 2022-08-05T12:21:17Z

Wayne Dixon replied August 5, 2022 12:21pm

Hi Anylmoi,
I like that you're trying things out - it's the best way to expand your knowledge.

That solution works, however, there are some drawbacks.

Firstly, the Bottom control will not pivot at the bottom of the geometry but rather the head of the bone, which will be offset be the length of the bone. (because it pivots from the head but connects via the tail)

This will make it harder to animate than it needs to be.

The other issue is the controls will not be aligned with the world. Their local Y axes will be aligned with the world Z. If you can, it's always better to have the local axes aligned with the world (you can't always do this though).

Having the controls line up with world space is very helpful for animators.

Hope that makes sense.