Simple way to rotate cornered objects

[Víctor Paredes]

This is a common animation task I always have to deal with. I just had the idea it can be easily done using a couple controlled bones:






The concept is very simple.
You have one bone on a corner and a second, child of the first one, on the other corner.
The layer/points are bound to the second bone.
The angle of Both bones are controlled by a third independent bone.
Then, to avoid double rotations, the bone of the left has angle constraints, so it can only rotate to the left; And the bone at the right has constraints so it can only rotate to the right.
Here's the file if you want to take a look:
https://www.dropbox.com/s/07lbfwqt1iy7s ... moho?raw=1

[Greenlaw]

Excellent Victor! I'm going to have to remember this one.

The way I've typically handled this was to place the layer in two groups, with each group's origin on different corners, and then I just rotate one of the groups. It's simple but this really only works when the rig isn't moving around.

I think yours is a more elegant setup, especially when the animation is more complicated. (More fun to animate with too.)

[lucasfranca]

Very good, thanks for this collaboration!

A question: what would the binding be like if the bones have zero strength?

[SimplSam]

Very cool. I like the way the bones - inter-play.

A question: what would the binding be like if the bones have zero strength?

Just Layer Bind the 'content' layer to the rightmost bone.

[lucasfranca]

Wow, yes! Simple! But why the one on the right? Well, anyway, it did.

[slowtiger]

This is the principle of the saloon door hinge.

[Víctor Paredes]

The way I've typically handled this was to place the layer in two groups, with each group's origin on different corners, and then I just rotate one of the groups. It's simple but this really only works when the rig isn't moving around.
I think yours is a more elegant setup, especially when the animation is more complicated. (More fun to animate too.)

Thanks. Yes, there are several ways to achieve this. Personally, in the past I simply created a couple smart bone actions and simulated the change of pivot there.
It works well, but it requires some work and can't be really recycled to other objects.
I preferred not to use layer rotation, because I normally want this rotation to be part of the rig, affecting other chains of bones.

Actually, the idea came days after I animated this:


Here the stool is parent of the entire character, because I needed the fish to react to the stool rotation.
In this example, I simple added two bones for the stool and animated them one at the time (which is way less fun and harder to tweak than just rotating one bone).
__

The content needs to be bound to the second bone to be sure it rotates following both bones.
If you bind the content to the first bone, then the content will only rotate following that bone and ignoring any rotation from the second bone.
If you bind it to the second bone, then the content will follow that bone, but also the first bone, since it is its parent.

[Greenlaw]

This is the principle of the saloon door hinge.

Haha, you're right!

[Greenlaw]

Wow, yes! Simple! But why the one on the right? Well, anyway, it did.

When rocking to the right, the right bone is lifting the bottle. When rocking to the left, the left bone is lifting the right bone (with the bottle) because the right bone is parented to it.

The middle bone controls only one of the two rocker bones at a time, and the difference between the two is the hierarchy. (Select the Parent Bone tool to see.)

[lucasfranca]

Based on your example, I thought of making a forearm that overlaps an arm, working for the joint break and without any action. Download here:
https://1drv.ms/u/s!Ah7UWMCgRFbGhKcdJjK ... Q?e=UrA41I