crt() puts the frame on a tube television. It has four parts, each a number in effect.uniforms, and a part at 0 is not there at all: scanlines (the dark lines between rows), mask (the colour grid of the tube, aperture stripes or slot cells with maskType), curvature (the bulge of the glass) and vignette (the corners going dark).
One line per row of the game, not of the screen. The lines follow the game's own pixels, like a console's picture on the tube. This example uses pixelRatio: 'device': on a dense screen each game pixel is two or three real ones, and the line fits inside the row. On a screen of density 1 a row is a single pixel, so every other row is darkened instead, and the mask is best left off.
It goes last in the chain: the palette or the dither decide which colours exist, and the tube is only where they are shown. Press 1 to 4 to toggle each part, M to change the mask type and Space to switch it off.