We were transforming coordinates for SVG gradients in a pretty
convoluted way: an inverse, unscaled transformation matrix was set up in
order to work around some (old?) technical limitations.
Rework this so the coordinate transformation no longer needs to be
inversed. This fixes gradients with "userSpaceOnUse" for its
gradientUnits attribute, which might cause coordinates to lie outside of
the bounding box of the gradient.
Two tests have updated reference screenshots with minor pixel updates;
this is probably the result of floating point precision improvements by
not inversing the matrix.
One test (svg-text-effects) has a bigger change: the gradient stops seem
to have moved along the text. This does seem to match other browsers
slightly better, so I'm moving forward with this ref update.
Skia painter is visibly faster than LibGfx painter and has more complete
CSS transforms support. With this change:
- On Linux, it will try to use Vulkan-backend with fallback to
CPU-backend
- On macOS it will try to use Metal-backend with fallback to
CPU-backend
- headless-browser always runs with CPU-backend in layout mode
This change will make it easier to disable screenshot comparison tests
on a specific platform or have per-platform expectations.
Additionally, it's nice to be able to tell if a ref-test uses a
screenshot as an expectation by looking at the test path.
