don't fix winding for empty paths

A path can be non-empty but become empty when it is simplified.
For instance, a path with the same rectangle, twice, with opposite
windings.

No contours are created for empty paths, so don't try to
fix their winding direction.

Additionally, check for a NULL coincidence since the
OpBuilder assumes that no concidence edges can be present
after the paths are simplified. This code should not get
called, but it's worth the future-proofing to check.

R=fmalita@chromium.org
BUG=502792

Review URL: https://codereview.chromium.org/1218863005

1 files changed, 4 insertions, 1 deletions

diff --git a/src/pathops/SkOpSpan.cpp b/src/pathops/SkOpSpan.cpp
index e89ec3e204..ae4771cffc 100755
--- a/src/pathops/SkOpSpan.cpp
+++ b/src/pathops/SkOpSpan.cpp
@@ -279,7 +279,10 @@ void SkOpSpan::detach(SkOpPtT* kept) {
     prev->setNext(next);
     next->setPrev(prev);
     this->segment()->detach(this);
-    this->globalState()->coincidence()->fixUp(this->ptT(), kept);
+    SkOpCoincidence* coincidence = this->globalState()->coincidence();
+    if (coincidence) {
+        coincidence->fixUp(this->ptT(), kept);
+    }
     this->ptT()->setDeleted();
 }