🚀 go-pugleaf

I have an Atari 1040ST, and I've been playing with its bit-mapped graphics.
One thing that the Mac does when running MacPaint is let you start a line
by clicking on a point, then flopping the other end around with the mouse until
you anchor it by clicking again. If the display is bit-mapped, what I'd 
expect to see is that every time the flopping line leaves a point on the 
screen, that point would have to be redrawn or you'd see a whole row of blank
points in every object crossed by the line. Yet this doesn't happen. Surely
the whole screen isn't redrawn every time a line is moved? An alternative
would be to have two planes which are automatically or-ed together to generate
the display, so one could be permanent and one temporary, but the ST certainly
doesn't do this--does Macintosh?
					--John Purbrick