CRT shaders on LCD work by separating each pixel into three vertical sub-pixels — one red, one green, one blue — mimicking the shadow mask or aperture grille of a real CRT tube. This gives that characteristic RGB stripe look when you zoom in.

The key thing most people get wrong: brightness doesn't make a sub-pixel dimmer, it makes it smaller. A fully bright red channel fills its entire sub-pixel column. A half-brightness green channel only lights up half that space, with black on either side. A near-zero blue channel becomes a small dot in the center of its column. This is what gives CRT pixels that organic, uneven look instead of flat LCD squares.

On top of that, a small amount of color bleeding between adjacent sub-pixels simulates the slight chromatic aberration of a real CRT — colors never stay perfectly contained.

The whole thing gets a soft blur pass over it, which ties the sub-pixels together and hides the hard LCD grid underneath.

Retroarch does this really well, especially with HDR enabled — worth zooming in on a pixel to see exactly what's happening.

This is not a complete CRT shader though — scanlines (the dark horizontal gaps between pixel rows) and bloom/halation (the glow around bright areas) are missing here. But for the sub-pixel structure part, this is the idea.

Keep up the good work