Expand the the final kernel4 stage to maintain a per-pixel mask.
Introduce two new path elements, FillMask and FillMaskInv, to fill
the mask. FillMask acts like Fill, while FillMaskInv fills the area
outside the path.
SVG clipPaths is then representable by a FillMaskInv(0.0) for every nested
path, preceded by a FillMask(1.0) to clear the mask.
The bounding box for FillMaskInv elements is the entire screen; tightening of
the bounding box is left for future work. Note that a fullscreen bounding
box is not hopelessly inefficient because completely filling a tile with
a mask is just a single CmdSolidMask per tile.
Fixes#30
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Path segments are unsorted, but other elements are using the same
sort-middle approach as before.
This is a checkpoint. At this point, there are unoptimized versions
of tile init and coarse path raster, but it isn't wired up into a
working pipeline. Also observing about a 3x performance regression in
element processing, which needs to be investigated.
