Currently, the pointer lines are drawn as complete X
windows (using the CreateWindow X call) and it is moved
1 pixel at a time.
This causes some issues with "trails" as windows behind
are re-drawn.
An ideal solution would be to draw a 100% transparent
window over the entire screen. Within this, draw the
pointer lines.
As of X11R6.8.0, transparent windows are supported, so
this should be possible, though I haven't worked out how.
