This is for the angle in degrees. Like this you can get any point on the
circle. Now if you want to get the points of an arc you could just
increase the angle a bit at a time and plot the points. But that would
not be a very nice circle and would be slow.
An option would be to get a starting point with the formula above and
then iterate with x2 + y2 = r**2. For example in the first part of
the circle between 0 and 45 degrees y is growing faster than x.
You would start with an y and increase it once by one.
( leave away the translation for easiness )