Hello,
This is just the matter of some pluses and minuses...
I have done this with the basic equation of circle :
x = cx + r * cos(theta)
y = cy + r * sin(theta)
here,
(cx, cy) is the center of the diagram,
(x, y) is the new reference point,
r is the radius and
theta is the angle which is varing.
Here is the full source code
