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Volumetric Light Beam

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