ps brush algorithm
on mousedown at (x,y):
set brush position to (x,y)
draw the brush
set remaining distance to granularity distance
when mouse moves to (x,y):
while distance from brush to (x,y) is greater than remaining distance:
move brush towards (x,y) remaining distance
draw the brush
set remaining distance to granularity distance
subtract the from remaining distance the distance from the brush to (x,y)
move brush to (x,y)
if the remaining distance is < 0
draw the brush
set remaining distance to granularity distance