Fix vertex alpha when connector edges intersect inner edges
In the new GM, the left and right portions of the path have a shared
vertex. The two edges leaving that vertex vertically towards the bottom
of the image are nearly parallel but the right edge has a steeper slope.
This leads to two sources of self intersections. The outset vertices
for the left and right sides intersect, which converts some of those
edges into "connecting" edges and removes others (preventing double
hitting of pixels). However, these outset but now "connecting" edges
from the right side also overlap with the inset vertices of the left
shape, requiring additional vertex splitting and connecting edge
creation.
The old alpha logic when one of the intersecting edges was a connecting
edge was to use its interpolated alpha value. In this case, since the
connecting edge originated from two outset vertices, its end point
alphas were 0 and the split alpha became 0, even though the other
intersecting edge was an interior edge.
This CL flips the logic around and ensures that any split vertex that
is on the interior edges remains fully opaque, any vertex that is
fully on the exterior remains fully transparent, and anything else
uses the max of the interpolated alphas (equivalent to the old
logic when one edge was connecting and one was exterior, but is more
accurate if somehow we get two connecting edges intersecting).
Bug: skia:11859
Change-Id: I85d2d54a8833e3c9da2fdd1a4f3a0513119730b9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/400596
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
2 files changed