Add new solver shape type: Traversal #59
Description
This is a big one.
There are shapes that turn on whenever one slider turns on. These are the main sliders.
There are shapes that turn on whenever multiple sliders turn on. These are combos.
Those two things give us access to all the shape extremes... but then we add progressions.
We can have a cheap shape turn on halfway to turning on a slider.
We can have a cheap shape turn on halfway to turning on a combo.
We can't currently have a cheap shape turn on halfway between two combos. This is a Traversal.
We can do it the expensive way using a free floating shape, and that's fine up to a point. However, that will only ever give us linear interpolation.
This would be an advanced option, and probably wouldn't be used too often. However, it would be nice for PSD like setups, and high quality eye shapes.
This probably requires a new tree for the ui, so this should wait until the trees are abstracted.