Two of the eight sheets carry fish instead of only plasma. Each fish cuts
straight across the slab once per cycle (thirty seconds, period preserved),
three per sheet, sizes spread by pow(hash, 2.6) so most are small and now
and then one is huge. Sheets sit near the front (0 and 1) so the silhouettes
are not buried under the layers in front of them; their alpha carries
coverage instead of depth.
The fish ride screen space, since the sheets themselves stretch up to four
times towards the frame edges, and are bent by the smooth swell of the
surface only: the crack steps flip the slope within a pixel and would slice
a fish to bits. Eyes are a small cold blue glow, the only light they have.
debug_fish.frag renders the shapes flat for inspection.
