The code is a “points-only” renderer. The design drives the OLED over the SPI pins and also outputs frame per second information via the serial port.
As you might expect, 3D output takes a good bit of math, and the chip in question isn’t very good at handling real numbers. [Ttsiodras] handles this using an old technique: fixed point arithmetic. The idea is simple. Normally, we think of a 16-bit word as holding unsigned values of 0 – 65535. However, if you choose, you can also use it to represent numbers from 0-50.999, for example. Mentally, you scale everything by 1,000 and then reverse the operation when you want to output. Addition and subtraction are straightforward, but multiplication and division require some extra work.
If you want to read more about fixed point math, you are in the right place. We’ve also covered a great external tutorial, too. But if you think this is the first time we’ve covered a 3D graphics engine for the ATmega parts, you’re wrong.