Custom Vertical ProgressBar in LibGDX

I want to create Custom vertical progress bar with non linear background

In previous implementation I used skin composer , but as I know it works perfect with simple regular shapes (the knob part resize on the all background image so it looks bad in my example ). I also try to hack using several layer behind the progress bar, but for this case the background behind progress bar is transparent.

I suppose this solution can solve my issue but unfortunately I dont understand how can I implemented that solution.

I also try to crop the inside part (that reference), whenever the progress is changed but I dont think that is the best solution (also the increase/decrase animation cannot be simple enabled )

Could you draw the full red progress bar and then load peices of it until it fills up the whole thing?

Here is a way to get pixels from a png image and you could wirrite your own parser:
How do I read pixels from a PNG file?

Or you could search Google for how to get peices of a png or bitmap.