tree 653fee0f68320709834091c290138baf05b11b8f
parent dc09cf810413a1c7adb88fc47852762866791a9a
author Brian Osman <brianosman@google.com> 1652213535 -0400
committer SkCQ <skcq-be@skia-corp.google.com.iam.gserviceaccount.com> 1652289530 +0000

SkLineClipper::IntersectLine - Fix out-of-bounds final result

The fuzzer found a subtle bug where our line vs. rect clipping could
produce points outside of the rect. Thanks to floating poing inaccuracy,
the first (horizontal) clip would produce a point just outside the
bounds. Then, we'd re-clip against the vertical segments - but go back
and start from the original points. Again, thanks to floating point,
we'd produce a point just outside the bounds.

The fix here is straightforward: After we've done the first clip
(reducing the magnitude of the values involved, and constraining the X
coordinates), use *that* as the new endpoints for the second clip.
Mathematically this is identical (the tmp values are new upper bounds on
the extents of the final endpoints after the first clip), but the math
is more stable this way.

Bug: chromium:1320467
Change-Id: I9c816110edb2944544243f2ad89665d5bc5c9c53
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/539196
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>