The finite precision of floating point computations can lead the coarse
renderer into inconsistent tile intersections, which implies impossible line
segments such as lines with gaps or double intersections. The winding number
algorithm is sensitive to these errors which show up as incorrectly filled
paths.
This change forces all intersections to be consistent.
First, the floating point top edge intersection test is removed; top edge intersections are
completely determined by left edge intersections.
Then, left edge intersections are inserted from the tile with the last top edge
intersection. The next top edge is then fixed to be the last tile with a left
edge intersection.
More details in the patch comments.
Fixes#23
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Eliminates the precision loss of the subtraction in the sign(end.x - start.x)
expression in kernel4. That's important for the next change that avoids
inconsistent line intersections in path_coarse.
Updates #23
Signed-off-by: Elias Naur <mail@eliasnaur.com>
This is a bit of a revert of the load-balanced ("more parallel") coarse
path rasterizer, but includes fills and also uses atomicExchange.
I'm doing it this way because it should be considerably easier to do
flattening in this structure, even though there will be some performance
regression.
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.
