Is there some formula/code out there that would compute the surface
of the intersection of two disks?
(of slightly different radiuses, and that can fully overlap).
I have started writing such a function, but it's full of special
cases and surface decompositions (disk slices, triangles, etc.),
and I'm not sure I am confident about the results it gives...
My aim is to use it to compute penumbra textures (for eclipses),
so it would essentially intersect a moon disk with a sun disk,
and use the remaining (visible) sun disk surface to compute lighting
Of course, I could always paint the two disks on a huge bitmap and
count color-coded pixels, but that isn't very satisfying. :)