Although not needed right now (checkerboarding backgrounds get
a slice anyway due to being a different scroll root), this will
be important for the upcoming work to make backdrop filter
roots implicit. This allows WR to know when slicing up a content
slice if the prim is relevant to the backdrop root.
Differential Revision: https://phabricator.services.mozilla.com/D146145
We need them for SVG primitives.
This patch adds a bit of plumbing to disable snapping some of the primitives and forcing the antialiasing shader feature where needed, and uses it for SVG solid rectangles and images.
Differential Revision: https://phabricator.services.mozilla.com/D139024
Glenn Watson