The DrawDeviceWithFilter function used to rely on SkImageFilter's
applyCTMForBackdrop, which would create a new DAG and use an
SkMatrixImageFilter node to account for the transformation. However,
that filter is really meant to perform a transformation prior to the
CTM matrix. Abusing matrix math to instead have it map the backdrop
contents back into the CTM local space grossly inflated the size of the
temporary images needed when under many perspective transforms.
This CL instead takes over control of the CTM decomposition and draws
the backdrop (src) content into a temporary layer directly, and then
feeds that through the image filtering. The code is somewhat cumbersome
to follow because of the combination of coordinate spaces and need to
make everything relative to the top left corner of the images.
When the rest of my image filter refactor is more underway, I believe that
a lot of the coordinate space math and image origin accounting will
be much cleaner, but the overall backdrop filtering strategy would remain
similar to this new implementation.
Bug: skia:9074
Change-Id: Ibd2995e81d2b308c74b2d298da5e38daa74c8677
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/239108
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
6d1c0d4196