What computer used that patent?
I'm not sure. I would think that patent more pertain to products like GEM based stuff (like Ventura Publisher and Atari ST), Windows, drawing software, etc. Anything that uses a mouse pointer that does not have hardware sprites.
Ideally you want a pointer that does not destroy the underling content as you move it about the screen. There are various ways to accomplish this. The Amiga way would be the Sprite.
The Cad Track thing worked on the basic principle that if you take any number and XOR or another number twice the end result is always same number you started with.
1 xor 4 xor 4 = 1
2 xor 4 xor 4 = 2
3 xor 4 xor 4 = 3
etc...
Lets say the 123 this is the contents of my screen and the 4's represent my pointer (shaped like a +).
123 xor _4_ = 163 xor _4_ = 123
123 xor 444 = 567 xor 444 = 123
123 xor _4_ = 163 xor _4_ = 123
I can place the cursor on the screen with one XOR operation and remove it with the second XOR. This is very fast because I don't need to save the underling contents of the screen in order to restore it.
The ugly but somewhat useful side-effect is that the pointer changes colors depending on the underling screen content.
This is useful because you can always see the cursor. You don't have the situation where you have a red pointer obscured because it is directly over a red object.
So, What computer used that patent? No Commodore computer I can think of. Perhaps some feature of the Bit Blitter?
That was the nail in Commodores coffin. Sad but true!
