Android Things demo project which controls WS2812B LED strip. Uses SPI bus for communication with strip. Can be used as a library for other projects.
For Raspberry Pi 3 connect strips's D_IN to GPIO10(SPI0_MOSI).
It uses blocks of 4 bits in SPI transmission to generate one bit of WS2812B protocol. Diagram below explains such usage of SPI.
Creative Commons CC0, see LICENSE.txt for details. Basically it means that this project is in the public domain.