Don't assume DecomposeCTM and setDeviceCoordSystem always succeed
Very originally, skif::Mapping::DecomposeCTM() and
SkBaseDevice::setDeviceCoordinateSystem assumed that if the canvas
matrix was invertible, then any scale decomposition would produce a
valid device coordinate system. This proved not to be true and fuzzers
quickly caught it, but I had attempted to address it by forcing
SkCanvas to do extra work so that the above two functions remained
unchanged.
However, it's become apparent that even making the assumption that the
product of two invertible matrices remains invertible does not always
hold true in the wonderful world of floating point math.
Instead, this rewrites DecomposeCTM and setDeviceCoordinateSystem to
return bools, allowing them to fail. This cleans up some of the earlier
checks that SkCanvas makes while computing the skif::Mapping, and it
also ensures that once we fold in the prior device's transform, the
net layer->global transform remains valid. If any of this fails, it
just gets rid of the new device and sets the clip to empty, basically
preventing drawing until the invalid layer has been restored.
Bug: chromium:1239968, chromium:1240685
Change-Id: Ib9ce8f95859e726a9eacf1154f6eef8dd3995500
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/442017
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
7 files changed