Fun XOR trick: using it to move a cursor across the screen without having to keep a buffer of the contents under the cursor (and putting them back).
It didn't always look great, but if you were moving a full-screen crosshair around, it was sufficient. Especially on hardware that was slow to move buffers to and from ram.
Unfortunately, using this pure-math technique was also patented until 2007 [0], much to the surprise of my former employer in 1986. Cadtrak had collected from companies like IBM and NEC and made a nice business as a troll.
Really? Apple ][ vector shapes had a XOR mode built in for non-destructively moving shapes across the screen, often used for cursors, and that was released in 1977.
It didn't always look great, but if you were moving a full-screen crosshair around, it was sufficient. Especially on hardware that was slow to move buffers to and from ram.
Unfortunately, using this pure-math technique was also patented until 2007 [0], much to the surprise of my former employer in 1986. Cadtrak had collected from companies like IBM and NEC and made a nice business as a troll.
[0] https://patents.google.com/patent/US4197590B1/en