The question how to rig characters with outlines has popped up multiple times.
This is an indicator that there is a lot of interest in the topic and not enough information available from other sources.
At times there were even some voices suggesting that, because our sample rigs don't have outlines, SMR as a system cannot be used to design and animate characters with outlines.
This should be enough to justify the existence of a short dedicated article.
In the world of digital cutouts outlines make life more difficult and complicate everything. This is why a large part of the character designs (and rigs) don't have any outlines at all, or only have partial in the facial area, hands, feet and some wrinkles here and there.
Ultimately, it is an artistic and stylistic choice.
Both approaches can be appealing, but outlines bring definition, contrast, and unmistakeable cartoony feel to character design.
Joint mechanics with or without outlines is more or less the same.
Type 1 joints, based on two overlapping circles are the most widely used, but even with this simple and unbreakable joint, we face complications, coming from the overlap of the outlines and the wrinkle which forms because of this. Such a wrinkle suggests volume, and in most cases it is necessary to control how deep it goes, and how it develops while body parts fold and stretch.
With simple cartoony designs, with thin, almost rubberhose limbs it is possible to have untreated joints, and in most cases this will be stylistically acceptable.
When untreated joints are not acceptable, there are various approaches to making the wrinkles look more organic.
One is to have many variations as frames inside the symbols to choose from. This can produce artistically very good results, but requires constant attention and many frames inside the elements.
Another option is external patching.
A patch occupies a layer above the top element, animates in sync with the body parts, and partly covers the wrinkle.
Patches are hard-welded elements of the Smart Magnet Rig. They can be designed to reveal or cover a desired part of the intersecting line, and they do this dynamically, which makes them very functional and low maintenance.
They are especially effective with thin to medium-thick outlines, where tapering of the line is not an issue.
Patching needs to be done creatively, and even though there are universal principles of patch engineering and design, the specifics have to be decided on a character-by-character basis, and will be dependent on each individual design, details and proportions.
The following video demonstrates how joints with outlines function, and shows various methods of patching.