I'm not sure I understand correctly - I suppose you'd want to use the forum's CODE-thing for your ASCII-art up there.

Anyway, have you checked the window-parameter of a panel? It's probably the easiest way to achieve this for you, though you do need two variables for this. (or use pan_setwindow)

A better way would be using draw_quad. The x-coordinates of vOffs would then be something along the lines of (bmap_width/2*(1-HEALTH/100)) (assuming HEALTH goes from 0..100, whereas the x-coordinate of the size-parameter would be (bmap_width*HEALTH/100) [again assuming Health is 100 at max].
I'm not quite sure what happens with the y-coordinate (the height) in your example - you maybe need the same code as above but with _height.
Anyways, that should get you started.

Feel free to ask if you need more help!

Perhaps this post will get me points for originality at least.

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