Customizing the Rigify meta-rig, Constraints & Custom Drivers, what's the solution?

Question

basically as the title says I am interested in two things:

1. How do I add constraints (Copy Rotation, TrackTo, etc.) to bones in the metarig, and then have them created/applied to/copied to the appropriate bone layers when you click the generate button.
2. Similarly, same for drivers. If I add a driver to a bone in pose mode on the meta rig, I see that it appears in the ORG layer when I click generate. How would I go about adding custom drivers so they appear on the appropriate working bone layers? Ideally for following this tutorial here: https://www.youtube.com/watch?v=LnsYKGDpBtQ I basically would prefer not to redo this if I need to make a change to the meta rig.

If there are some alternative solution or workflow to get the end effect, I'd be interested. I am tempted just to make my own rig, but some of the template subrigs like tentacle are very useful though, especially the IK/FK setup and that seems to be a pain to learn how to make.

Answer 1

Adding constraint and relinking to a @bone_name/@CTRL/@DEF/@MCH bones is easy with basic.raw_copy & basic.super_copy

Turn on "Relink Constraints"

Go to its constraint rename the constraint to the desired target. e.g "Copy Rotation" > "@ORG-thigh.L" without those "", you can leave the target blank and it will still work, unless it's a "stretch to"

it was quite confusing with Blender's official doc, because there were no example. I learned it from this doc:

https://epicgames.github.io/BlenderTools/ue2rigify/advanced/relink-constraints.html

Answer 2

You can't, at least not easily. The only rig type that preserves constraints after generation is the Raw Copy. And that one is pretty advanced and I am not sure what the correct usage for it is. The only thing that would work without serious coding knowledge is to finalize your meta rig and add your constraints on the generated rig.