This isn't real volumetric fog — it's a flat 2D quad that looks volumetric.
Valve shipped this exact trick in Half-Life 2 back in 2004 (map d1_canals_08).
Twenty years later it still holds up because your brain fills in the rest.
The vertex shader does cylindrical billboarding: a cross product between the camera direction and the beam axis gives a "right" vector, so the quad always faces you but stays locked to its axis. A dot-product fade hides the paper-thin edge when you look straight down the beam.
The fragment shader draws a cone shape via pow(uv.y, 1-curve) width interpolation,
soft edges with smoothstep, and three scrolling noise samples (two for alpha, one for distortion)
that fake drifting dust. World-position offsets give each beam unique noise.
Cost: near zero. One shared shader program, .clone() for per-beam uniforms,
additive blending, no depth writes, procedural canvas noise — no external textures needed.
Raymarching this would murder your framerate; this doesn't.
Original Concept (Godot):
Passivestar Blog Post
Bluesky Thread
PORTED BY TRENT STERLING / TRONT AND GEMINI 3 PRO