When only anchors of a path or compound path move, the area an edit
changed is now the box of the segments that start or end at a moved
anchor (and the line that closes an open subpath's fill at a moved
end), before and after, grown by the farthest the strokes reach. The
canvas then draws that part of the frame again instead of the whole
object. Objects with a non-solid paint, dashes, a width profile,
arrowheads, a brush, effects or an opacity mask still count whole.
At 1600 x 1200, single-threaded, the frame after one anchor of a filled
closed path moves takes 16.6 million CPU cycles instead of 56.4 million
with 50,000 anchors, and 65.6 million instead of 180.0 million with
200,000 anchors.
dotCooCoo
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