Fortunately it seems this is largely unused (I can see 5 invocations when running all LO tests), so I went for the crude approach of redirecting all drawing to a temporary bitmap and then manually xor-ing all the data after each draw operation. This could be optimized if needed.
Change-Id: I6fc91362dd93188775b371d5548a68a58645f85c Reviewed-on: https://gerrit.libreoffice.org/c/core/+/86776
dfe106c8a939 implement xor drawing for Skia
vcl/inc/skia/gdiimpl.hxx | 8 +++
vcl/qa/cppunit/BackendTest.cxx | 13 ++++-
vcl/skia/gdiimpl.cxx | 108 ++++++++++++++++++++++++++++++++---------
3 files changed, 104 insertions(+), 25 deletions(-)