Ice slab with layered plasma, two-pass refraction

Pass 1 renders eight plasma sheets into an atlas with linear depth in alpha;
pass 2 marches the refracted ray to each sheet and absorbs it by real path
length, so near and far layers separate under pointer parallax. Plasma cycle
repeats exactly every 30 s; - / = change speed.

shot.py

@@ -0,0 +1,11 @@
+#!/usr/bin/env python3
+"""shot.py <page.html> <out.png> [t] [size]  — single still of a live page (uses its #shot mode)."""
+import os, subprocess, sys
+page, out = sys.argv[1], os.path.abspath(sys.argv[2])
+t = sys.argv[3] if len(sys.argv) > 3 else "0"
+w = sys.argv[4] if len(sys.argv) > 4 else "700"
+url = "file://" + os.path.abspath(page) + "#shot&t=%s&w=%s" % (t, w)
+subprocess.run(["firefox","--headless","--new-instance","--profile","/tmp/ff2",
+                "--window-size=%s,%s" % (w, w), "--screenshot=" + out, url],
+               env={**os.environ,"MOZ_NO_REMOTE":"1"},
+               stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, timeout=180)