WDEF creates a window of a set size. The first example will make a 512
512 window in the
top right hand corner of your screen. The second example makes a 128128 window,
and the last example makes a 900512.
IDL> wdef,0
IDL> wdef,0,128
IDL> wdef,0,900,512
Window 1 is in the lower right, 2 is in the upper left, and 3 is in the
lower left (even windows on top, window modulo 4 equaling 0 or 1 is on the
right)