Classify spot shadows for general shapes

Add some simple checks so we can tell whether a shadow's umbra is
completely covered by the occluder, partially covered, or less than
halfway covered.

Change-Id: I092281c4933bd0380946eb0fdd458ce04b0d713c
Reviewed-on: https://skia-review.googlesource.com/16603
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
1 file changed