Blinking bar

[juster-0]

The bar sometimes "blinking" while changing values.

xob_blinks-2022-07-14_11.45.12.mov

After checking the video frame by frame, I've noticed that blinking is the result of redrawing the bar every time, when values change.

To solve the issue we can redraw only changed part of the bar. And draw all components of the bar separately.

[florentc]

This may be related to #37. Could you confirm the bug is introduced by commit ff4911e just as suggested by @cdown in #37?

[juster-0]

Yes, it occurs after the commit, but only if enable_alpha=yes. I also have fixed it in #47.