pixel

What a shader's function is given about the pixel it is working out. (Call that value pixel, and the editor shows these as you type.)

Where the pixel is on the screen: x from 0 (its left edge) to 1 (its right edge), y from 0 (its top) to 1 (its bottom).

pixel.screen(place)

The picture's colour at a place: 4 parts, r, g, b and a. pixel.screen(pixel.at) is the pixel as it is.

Seconds since the level began.

The beat the level is at.

The screen's size in units, x and y. It is always 1080 units tall, so pixel.at * pixel.size is the pixel's place in units.