info-mac@uw-beaver (01/03/85)
From: winkler@harvard.ARPA (Dan Winkler) Try this in MacPaint: 1. Draw any shape (let's say an oval) in the brick pattern 2. Select it with the lasso 3. Invert 4. Deselect 5. Select again 6. Invert again (Your oval will still exist here) 7. Deselect again (Poof! Your oval will be gone) How can two inversions erase a pattern? It seems counter-intuitive at first, but if you try it and think about it you'll see that this is the correct behavior because of the definition of the lasso. (This doesn't happen when you select with the rectangle of marching ants.) This phenomenon is not specific to the brick pattern. In fact, no pattern can withstand repeated select-invert-deselect. Some patterns, like black, die after once through this loop. The brick pattern dies after twice through. Other patterns slowly melt away, dying in a number of steps proportional to their size. But no pattern can survive indefinitely since each time through all the outermost black pixels turn white and are lost to the white background when the region is deselected. Sorry if you think this is obvious. I for one was pretty suprised when my oval suddenly disappeared for the first time. Dan. (winkler@harvard)