Making scrollable backgrounds

Scrolling backgrounds are formed using a set of sprites positioned directly next to each other. A sprite is only 16 pixels wide so many are needed to fill the screen horizontally. The Sticky_bit is often used to make this simpler. A set of 21 chained sprites can be used to make a single full-screen scrolling background layer.

Updating VRAM
todo

Demos
Interactive demos with source can be found here

todo: clean it up, make scroll3, finish documenting it here