Hi, i'm testing out the new "Otis" muscle system in houdini 21 and i've noticed that there seems to be no way to explicitly attach a specific muscle to a specific bone. instead of just the closest bone to the muscle geo.
This is very frustrating when you're dealing with a quadroped character and all of it's leg muscles are attaching to the ribcage.
In the previous iteration of the muscle system, you could select which bones would attach to wich muscles in the configure constraints node, but in the new Otis system i don't see any options anywhere to tell the bicep muscle for example to not attach to the ribcage.
Has anybody else encountered this issue and have you found a fix?
Otis does not make use of Muscle-to-Bone constraints other than the Muscle End constraints. In Vellum, you could only specify Attachment Candidates for Muscle-to-Bone constraints, not for Muscle End constraints, so when it comes to Muscle Ends, there is no difference between Otis and Vellum.
Having said that, I can understand that not being able to set an Attachment Candidate for your Muscle Ends must be frustrating. We can look into adding that in the future, but for the time being, here are some things that you can adjust to get it working better:
Ensure that the ends of your leg muscles are in the anatomically correct place, i.e. near the bone they should attach to. This will also help to ensure that the autotensionlines will attach to the bones at the correct points.
Ensure that the muscleendmask has a value of 1 at the ends of the muscles where the attachment should happen, and is zeroed out where you don't want attachment constraints to form from.
Reduce the Muscle Ends Distance Threshold on the Muscle Constraint Properties Otis node for the relevant muscles.
Decrease the Muscle End Mask Threshold on the Otis Muscle and Tissue Configure Node if you don't want to fiddle with the falloff of the muscleendmask.
Finally, you can actually specify a muscleendmask attribute on your bones. Initialize it to 1 everywhere, and then you can set it to 0 in the regions where you don't want attachments to form. I've discovered a bit of a bug with this method, namely that the mask must be exactly 0, and can't just be a very small number (which happens if you use an attrib paint/muscle paint). I will try to fix that soon, but for now you can use something like an attribute remap with the input min set to something small like 0.0001, and that should fix it.
