got zoom +/- working pretty nicely.
but after some re-arranging, i’m getting what i call
aliasing, as proportion of a fairly fine (2 coordinate points)
line is zoomed in: at one to more zoom sizes the width is
wrong – no doubt because of the ratio of total dimensions
to the zooming increment factor
-which is +0.0999999999999999778
panel size is 900 x 472 but that doesn’t seem to play much
part because i’ve been changing it.
this is either a horrible trial and error thing, or i may have
to compromise on that zoom ration and number of sizes available.
(it’s the figure Possemo used in a method, worked fine until
just now when i changed things)