i'm trying to make a circular energy bar right now in a similar vein and need to erase the bar in a circular manner, it overlays on top of the game on the HUD, I was wondering if any of these functions mentioned would be applicable?
You could make a half-circle with the erase effect, then place it's hotspot in the center of the flat side, like so:
Then when health is depleted, rotate the half-circle.
To make a full circle, create the second half of the health bar and the second half of the eraser on a separate layer.
I can't think of any efficient way to keep the circle in one piece and still use the erase method. But you could do it without the erase method by animating a bunch of separate sprite frames for the circle itself, even though that might be a bit tedious. Though in the long run it might actually be the best way. You could have the same number of frames as you do units of health, so it would just be a matter of setting the animation to frame (value.health) or whatever. Longer to set up, but way easier to code for.