crt_scanlines

A CRT line texture over the finished frame — the demo opener's grain.

Every period framebuffer rows, thickness of them are darkened by strength. Because it reads frag_coord, the line pitch follows the real output resolution rather than any layout unit, so it looks the same whatever the frame is rendered at.

property	default	what it does
period	6	rows between one line and the next
thickness	2	rows darkened out of each period
strength	0.30	how far those rows are darkened, 0–1

Why it is a shader

The opener is a zui screen whose whole tree is rebuilt every frame. Drawn in that tree, this texture was one absolutely-positioned box per line — 240 nodes built, laid out and drawn every frame, which measured about half the sequence's frame cost. As a full-screen pass it costs one draw and touches no nodes.

Using it

preseed/parts/p_coldstart installs it on enter and removes it on exit:

local shader = asset.resolve("crt_scanlines", "shader")
tools.use("pp", "add", "crt_scanlines", { shader = shader, priority = 100 })