I'm trying to implement radial gradients in some open-source projects (cairo and pixman), based on the PDF specification.
The specification does not say explicitly how to handle the case when the start and end circle are tangent, but from my understanding the non-negative radius clause applies to them as well, so they should paint just an half-plane (even if Extend is true).
An example of such gradients is available here:
http://people.freedesktop.org/~ranma42/radial-gradients/
The png files show what I believe would be the correct rendering of the pdf's.
Adobe Reader paints the whole plane when it encounters these gradients, but Apple Preview shows them as I would expect.
What should happen when the two circles are tangent?
Is my interpretation of the specification (and thus my rendering) correct?