I have a tiny feature request, which from what I can tell and tested should really not cause any issues.
In tk2dUIProgressBar could the paremter 'initializedSlicedSpriteDimensions' be made public?
A use case for this, is you have a progress bar which will be resized (or even sized once during set up), and you'd like to basically mark it as dirty so the 'fullSlicedSpriteDimensions' are recalculated.
Since that's all it really does, it doesn't seem like it'd have any side effects - what do you say?