@SilverWarrior, thanks for reply, and good points. I shall try and get backgound images in the correct size and avoid scaling for the reasons you describe!
Drawing manipuation...
(Background, this is for dawing a sailing "race course" around a set of "Mark" shapes (circles) - user clicks each mark of the course in turn. a Polyline stores vertices at centre of each Mark. (circular shape) in turn. So far, so good! SO have a set of straight lines vertices on each mark Shape.
But course "rules" are do NOT sail over a mark but sail round it either clockwise or anticlockwise
User can click each Mark to change color Red/Green to indicate.
So next, I would like to replace each straight-line vertex with a smooth transition (arc or ellipse). going round each Mark in the correct direction (leave Mark to either Left or Right.
Maybe have to work out the angle of each of the two lines at a Mark, and then work out how to describe the Arc! Seems tricky! Is that a valid approach do you think? any ideas to simplify?