https://nbickford.wordpress.com/2011/04 ... algorithm/
What I've read elsewhere is that making a circle on a bitmapped display (or possibly LEDs) is possible with add, subtract and shift operations.
The algorithm is important to master because it could be used for LEDs as well.
Other biographical information to aid in understanding and locating this information:
From: PROGRAMMING HACKSITEM 149 (Minsky): CIRCLE ALGORITHM
Here is an elegant way to draw almost circles on a point-plotting display:
NEW X = OLD X - epsilon * OLD Y
NEW Y = OLD Y + epsilon * NEW(!) X
This makes a very round ellipse centered at the origin with its size determined by the initial point. epsilon determines the angular velocity of the circulating point, and slightly affects the eccentricity. If epsilon is a power of 2, then we don't even need multiplication, let alone square roots, sines, and cosines! The "circle" will be perfectly stable because the points soon become periodic.
The circle algorithm was invented by mistake when I tried to save one register in a display hack! Ben Gurley had an amazing display hack using only about six or seven instructions, and it was a great wonder. But it was basically line-oriented. It occurred to me that it would be exciting to have curves, and I was trying to get a curve display hack with minimal instructions.
http://www.cl.cam.ac.uk/~am21/hakmemc.html
https://en.wikipedia.org/wiki/Marvin_Minsky
External Credit due to:
http://forums.parallax.com/discussion/1 ... -and-shift
