Fractal tunnel: writing raymarch depth so a million points are occluded properly

The fourth prompt switches to raymarching, and its technical difficulty is specific — the hardest of the four to get right by luck. A raymarched fractal is solved per ray in the fragment shader and writes no depth by default; the dust is a million ordinary THREE.Points going through the normal rasterisation pipeline. For the two to occlude each other correctly, the raymarch hit distance has to be converted back into depth and written out. Skip that and the particles float in a sheet in front of the fractal, which anyone can see is fake.

Three rounds of visual iteration, 30 tool calls. First frame in about 1.6–2.1 seconds under SwiftShader, no JS errors and no GLSL errors, matching hashes for the fixed-time screenshot; pause, parallax, zoom, palettes, downsampling and resize all verified.

The HUD on the poster and the “Into the infinite.” typography were not in the prompt. The difference from the Fable 5.1 run is mostly one of taste: this one leans product-page, with sparser fractal structure and clearer separation, while that one is far denser and feels more like being inside the sponge.

Controls: mouse movement to look around, scroll to adjust FOV, space to pause, 1/2/3 for the three spectra (Ion Bloom, Ember Vault, Glacial Veil), ?t= to freeze the clock.