More details are in the bug, but the specific test case gets an
overlap region in the AA outset geometry for the left and right shapes.
Additionally, the mitered outset for the left shape is collinear with
the bottom of the right shape, so the winding of exterior edge of
the overlap region is updated to +2.
When determining the polygons to fill, this +2 on the outer edges
violates the winding rules that normally ensure the interior polygons
(that use +/-2 instead of +/-1) are always filled.
It appears a similar bug fix was added here:
https://skia-review.googlesource.com/c/skia/+/141952/
but then didn't survive a heavy refactor later:
https://skia-review.googlesource.com/c/skia/+/215094
To the best of my knowledge, this is achieving the same result as the
original fix but is updated to preserve winding scale for interior
polygons with overlap regions (the code checks for these, but they
seem pretty rare to me).
Bug: 1197461
Change-Id: I0d32820af8cfec92c46114aeaa58b6e340abdfca
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/397140
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
70fae35842