The engine has a screen effect for most of the looks a game of the era reached for. Each is a function that returns a whole effect, spread into usePostProcess, and each knob is a number in effect.uniforms you can write every frame: here mosaic grows and shrinks, the shockwave ring moves out and starts again, and the glitch comes in bursts.
Some read the frame more than once. bloom, godrays, blur and tiltShift work in passes at half or a quarter of the game's size, so a wide glow costs about what a narrow one does. Two remember the last frame: phosphor leaves a short trail behind bright things, and lcd the ghost of a slow handheld panel. That costs two pictures the size of the canvas while they run, which is why only they ask for it.
Order matters, as in any chain: grade and distort first, then whatever adds light, then a palette or a dither, and the screen (phosphor, ntsc, lcd, crt) last. Press left and right to step through them.