Pre-construct device-to-layer matrix for skif::Mappings
SkCanvas and SkDevice were using SkM44 and its definition of invert(),
but it was slightly more generous than SkMatrix::invert() so the fuzzer
caught a case where the layer's SkDevice had a valid transform but then
converting it to a SkMatrix in skif::Mapping was no longer invertible.
This modifies it so that skif::Mapping no longer tries to invert the
matrices. In almost all cases, the inverse of the layer-to-device
matrix can be constructed directly from a matrix multiply (that's what
device->getRelativeTransform() does). When the matrices are
ill-conditioned the constructed inverse may be inaccurate (hence why
SkMatrix::invert reports false), but in practice this happens for
ridiculously large transforms and the error isn't significant compared
to the precision range of the matrices anyways.
Other cases explicitly want to use the identity matrix for the layer
to device matrix, so I added a helper in the few places that would have
had to pass SkMatrix::I() twice instead.
The last case is drawImage() that creates its own skif::Mapping, now it
just calculates the inverse that skif::Mapping() would have done and if
it fails it drops the draw since it means the canvas matrix is bad.
Bug: chromium:1276525
Change-Id: Ib516bb2fac19d5e7397bd27d80f8e3932b25b2e2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/509396
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
5 files changed