diff --git a/10_ice_fish.frag b/10_ice_fish.frag
new file mode 100644
index 0000000..8985f1e
--- /dev/null
+++ b/10_ice_fish.frag
@@ -0,0 +1,154 @@
+// Pass 1: eight plasma sheets, one atlas tile each. Alpha stores linear depth,
+// except on the three sheets that carry the fish: there it stores how much of the
+// pixel the fish covers, so the ice pass can draw them as solid dark shapes.
+// Density field lit as a height surface: billowing volumes with a real terminator.
+precision highp float;
+uniform vec2 u_res; // size of one tile
+uniform float u_time;
+
+float hash(vec2 p) { return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }
+float noise(vec2 p) {
+  vec2 i = floor(p), f = fract(p);
+  f = f*f*(3.0-2.0*f);
+  return mix(mix(hash(i), hash(i+vec2(1.0,0.0)), f.x),
+             mix(hash(i+vec2(0.0,1.0)), hash(i+vec2(1.0,1.0)), f.x), f.y);
+}
+float fbm(vec2 p) {
+  float sum = 0.0, amp = 0.5;
+  for (int i = 0; i < 4; i++) {
+    sum += amp * noise(p);
+    p = mat2(1.62, 1.17, -1.17, 1.62) * p;
+    amp *= 0.5;
+  }
+  return sum;
+}
+float fbm2(vec2 p) {
+  return 0.5 * noise(p) + 0.25 * noise(mat2(1.62, 1.17, -1.17, 1.62) * p);
+}
+
+// Silhouette of a fish: pointed nose, deepest just behind the head, a narrow
+// peduncle, then a tail fan with a fork cut out of it. One width function, so the
+// whole animal is guaranteed to be a single connected shape.
+float smin(float a, float b, float k) {
+  float h = clamp(0.5 + 0.5 * (b - a) / k, 0.0, 1.0);
+  return mix(b, a, h) - k * h * (1.0 - h);
+}
+float sdTriangle(vec2 p, vec2 p0, vec2 p1, vec2 p2) {
+  vec2 e0 = p1 - p0, e1 = p2 - p1, e2 = p0 - p2;
+  vec2 v0 = p - p0, v1 = p - p1, v2 = p - p2;
+  vec2 q0 = v0 - e0 * clamp(dot(v0, e0) / dot(e0, e0), 0.0, 1.0);
+  vec2 q1 = v1 - e1 * clamp(dot(v1, e1) / dot(e1, e1), 0.0, 1.0);
+  vec2 q2 = v2 - e2 * clamp(dot(v2, e2) / dot(e2, e2), 0.0, 1.0);
+  float s = sign(e0.x * e2.y - e0.y * e2.x);
+  vec2 d = min(min(vec2(dot(q0, q0), s * (v0.x * e0.y - v0.y * e0.x)),
+                   vec2(dot(q1, q1), s * (v1.x * e1.y - v1.y * e1.x))),
+                   vec2(dot(q2, q2), s * (v2.x * e2.y - v2.y * e2.x)));
+  return -sqrt(d.x) * sign(d.y);
+}
+// Half-height of the body at x: pointed nose, deepest a quarter of the way back,
+// then down to a narrow peduncle. Sweeping a circle along it keeps the body one piece.
+float fishWidth(float x) {
+  float t = clamp((1.15 - x) / 2.30, 0.0, 1.0);        // 0 at the nose, 1 at the peduncle
+  return 0.34 * pow(sin(3.14159 * pow(t, 0.55)), 0.8) + 0.05 * smoothstep(0.70, 1.0, t);
+}
+float sdFish(vec2 p) {
+  float d = length(vec2(max(abs(p.x) - 1.15, 0.0), p.y)) - fishWidth(p.x);      // body
+  // tail: two lobes fanning back from the peduncle, with a notch between them
+  d = smin(d, sdTriangle(p, vec2(-1.02, 0.03), vec2(-1.62, 0.09), vec2(-1.46, 0.52)), 0.08);
+  d = smin(d, sdTriangle(p, vec2(-1.02, -0.03), vec2(-1.62, -0.09), vec2(-1.46, -0.52)), 0.08);
+  // dorsal and pectoral fins
+  d = smin(d, sdTriangle(p, vec2(0.22, 0.20), vec2(-0.06, 0.46), vec2(-0.40, 0.16)), 0.05);
+  d = smin(d, sdTriangle(p, vec2(0.46, -0.16), vec2(0.26, -0.08), vec2(0.10, -0.28)), 0.04);
+  return d;
+}
+
+const float EXTENT = 3.8; // half-width of a sheet in world units; must match the ice pass
+
+void main() {
+  vec2 tile = floor(gl_FragCoord.xy / u_res);
+  float layer = tile.x + tile.y * 4.0;
+  vec2 uv = fract(gl_FragCoord.xy / u_res);
+  vec2 p = (uv - 0.5) * 2.0 * vec2(EXTENT * u_res.x / u_res.y, EXTENT);
+  p *= 0.85 + 0.10 * layer; // far sheets carry finer detail, which reads as distance
+  float angle = hash(vec2(layer, 3.1)) * 6.2831853;
+  p = mat2(cos(angle), sin(angle), -sin(angle), cos(angle)) * p;
+
+  // Periodic time: every field returns exactly after 30 seconds.
+  float phase = u_time * 6.2831853 / 30.0;
+  vec2 o = vec2(cos(phase), sin(phase));
+  vec2 seed = vec2(layer * 17.3, layer * 9.1);
+
+  // Two nested warp stages, the marbled-plasma motion.
+  vec2 q = vec2(fbm(p * 0.50 + seed + o * 0.55),
+                fbm(p * 0.50 + seed + 23.1 - o * 0.55));
+  vec2 r = vec2(fbm(p * 0.85 + 2.0 * q + seed + vec2(o.y, -o.x) * 0.40),
+                fbm(p * 0.85 + 2.0 * q + seed + 31.7 - vec2(o.y, -o.x) * 0.40));
+  vec2 w = p * 1.10 + 2.6 * r + seed;   // warped coords of the density field
+
+  // The silhouette is shared by all sheets (slid a little per depth), so the gaps
+  // stay open right through the stack instead of filling in with overlap.
+  float mass = smoothstep(0.520, 0.548, fbm((p + o * 0.30 + vec2(0.10, -0.07) * layer) * 0.62 + r * 1.1 + 13.7));
+
+  // Light the density as a height surface: $cheap 2-octave gradient, strong terminator.
+  float h = 0.05;
+  vec2 slope = vec2(fbm2(w + vec2(h, 0.0)) - fbm2(w - vec2(h, 0.0)),
+                    fbm2(w + vec2(0.0, h)) - fbm2(w - vec2(0.0, h))) * (10.0 / (2.0 * h));
+  vec3 nrm = normalize(vec3(-slope, 1.0));
+  float lit = clamp(dot(nrm, normalize(vec3(-0.38, 0.52, 0.76))), 0.0, 1.0);
+
+  // Folded planes across the volume, feathered so they never read as a grid.
+  vec2 g = (p + r * 2.0) * 1.4;
+  vec2 cell = floor(g), f = fract(g);
+  float feather = smoothstep(0.0, 0.10, min(min(f.x, 1.0 - f.x), min(f.y, 1.0 - f.y)));
+  float facet = mix(1.0, mix(0.70, 1.25, hash(cell + seed + step(1.0, f.x + f.y) * 37.0)), feather);
+
+  float shade = 0.05 + 1.10 * lit * lit;                // lit tops, near-black undersides
+  float e = mass * facet * shade * 0.085
+          + mass * (1.0 - mass) * 4.0 * 0.040           // thin torn silhouette
+          + mass * pow(lit, 14.0) * 0.110;              // glint where a fold faces the light
+  vec3 col = e * mix(vec3(0.02, 0.42, 0.60), vec3(0.08, 0.64, 0.88), facet * 0.5);
+  // Faint dye in the open gaps so darkness reads as depth, not as a hole.
+  col += smoothstep(0.40, 0.85, fbm(p * 0.30 + seed * 0.4 + o * 0.3)) * vec3(0.0003, 0.0011, 0.0015);
+
+
+  // Two sheets carry fish. Each one cuts straight across the slab once per cycle,
+  // with long gaps and a wide spread of sizes: mostly small, now and then something
+  // far too big. They are almost pure black, so all you ever see is the silhouette
+  // eating into the glow behind them, bent by the cracks in the ice.
+  float cover = (0.42 + layer * 0.26) / 2.6; // the sheet's own opacity, except where a fish is
+  if (layer == 0.0 || layer == 1.0) {
+    vec2 sp = (uv - 0.5) * 2.0 * vec2(EXTENT * u_res.x / u_res.y, EXTENT);
+    float t01 = u_time / 30.0;
+    for (int k = 0; k < 2; k++) {
+      float id = float(k);
+      float lt = fract(t01 + hash(vec2(layer, id)));
+      if (lt < 0.02 || lt > 0.98) continue;
+      float dir = hash(vec2(id, layer + 5.0)) > 0.5 ? 1.0 : -1.0;
+      float y0 = (hash(vec2(id, layer + 13.0)) - 0.5) * 4.6;
+      float y1 = y0 + (hash(vec2(id, layer + 17.0)) - 0.5) * 1.8;
+      vec2 pos = mix(vec2(-dir * 8.6, y0), vec2(dir * 8.6, y1), lt);
+      float tilt = atan((y1 - y0) / 17.2);
+      float size = 0.30 + 1.30 * pow(hash(vec2(id, layer + 3.0)), 2.2);
+      vec2 q = (mat2(cos(tilt), -sin(tilt), sin(tilt), cos(tilt)) * (sp - pos) * vec2(dir, 1.0)) / size;
+      float d = sdFish(q);
+      float px = 0.019 / size;
+      float cov = clamp(0.5 - d / px, 0.0, 1.0);
+      if (cov >= 0.0) {
+        // A dark body, a faint halo where the ice is lit around it, and two small
+        // eyes that burn cold blue: that is the only thing that says "alive".
+        float halo = max(clamp(0.5 - (d - 0.16) / (px * 6.0), 0.0, 1.0) - cov, 0.0);
+        col += vec3(0.006, 0.020, 0.032) * halo;
+        if (cov > 0.0) {
+          col = mix(col, vec3(0.0010, 0.0014, 0.0018), cov);
+          float eye = smoothstep(0.045, 0.012, length(q - vec2(0.80, 0.095)));
+          eye += 0.22 * smoothstep(0.11, 0.0, length(q - vec2(0.80, 0.095)));
+          eye += 0.07 * smoothstep(0.26, 0.0, length(q - vec2(0.76, 0.05))); // the head catches it
+          col += vec3(0.06, 0.44, 0.80) * eye * cov;
+          cover = 1.0;
+        }
+      }
+    }
+  }
+  float alpha = (layer == 0.0 || layer == 1.0) ? cover : (0.42 + layer * 0.26) / 2.6;
+  gl_FragColor = vec4(col, alpha);
+}
diff --git a/11_ice_over_fish.frag b/11_ice_over_fish.frag
new file mode 100644
index 0000000..8a52868
--- /dev/null
+++ b/11_ice_over_fish.frag
@@ -0,0 +1,137 @@
+// Pass 2: clean ice. Refraction, chromatic shear, absorption by true path length.
+// Nothing is added to empty space, so the gaps between sheets stay black.
+precision highp float;
+uniform vec2 u_res;
+uniform float u_time;
+uniform vec2 u_mouse; // normalized, bottom-left origin
+uniform sampler2D u_scene;
+uniform vec2 u_tile_res;
+
+const float EXTENT = 3.8;                 // must match the plasma pass
+const float FRONT  = -2.0;                // ice surface, camera at the origin looking down -z
+const vec3  SIGMA  = vec3(0.66, 0.26, 0.11); // absorption per unit: red dies first, so depth turns blue
+const float IOR    = 1.31;
+// The fish sheets store coverage in alpha, so their depth comes from the index.
+
+float hash(vec2 p) { return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }
+float noise(vec2 p) {
+  vec2 i = floor(p), f = fract(p);
+  f = f*f*(3.0-2.0*f);
+  return mix(mix(hash(i), hash(i+vec2(1.0,0.0)), f.x),
+             mix(hash(i+vec2(0.0,1.0)), hash(i+vec2(1.0,1.0)), f.x), f.y);
+}
+float fbm(vec2 p) {
+  float sum = 0.0, amp = 0.5;
+  for (int i = 0; i < 3; i++) { sum += amp * noise(p); p = mat2(1.62, 1.17, -1.17, 1.62) * p; amp *= 0.5; }
+  return sum;
+}
+float fbm2(vec2 p) {
+  return 0.5 * noise(p) + 0.25 * noise(mat2(1.62, 1.17, -1.17, 1.62) * p);
+}
+vec2 atlasUV(vec2 world, float layer) {
+  vec2 uv = world / (2.0 * EXTENT) + 0.5;
+  uv = clamp(uv, 0.5 / u_tile_res, 1.0 - 0.5 / u_tile_res); // keep bilinear taps inside the tile
+  return (vec2(mod(layer, 4.0), floor(layer / 4.0)) + uv) / vec2(4.0, 2.0);
+}
+// The slab's fracture lines: two families of long, slightly wandering cracks. Shared
+// by the height field and the sheen, so each crack is both a bright seam and a step.
+vec2 fracture(vec2 x) {
+  float d = fbm(x * 0.62 + 3.0) - 0.5;                 // zero set: long winding cracks
+  float e = fbm(x * 1.35 - 7.0) - 0.5;                 // a sparser second family
+  return vec2(d, e);
+}
+// Frozen surface: fine ridged grain over the plates the cracks have lifted apart.
+// Static in world space; only the plasma behind it moves.
+float heightSmooth(vec2 x) {
+  return 0.090 * (1.0 - abs(2.0 * fbm2(x * 2.2 + 2.0) - 1.0))
+       + 0.055 * (1.0 - abs(2.0 * fbm2(x * 6.4 - 5.0) - 1.0));
+}
+float height(vec2 x) {
+  vec2 fr = fracture(x);
+  return heightSmooth(x)
+       + 0.014 * clamp(fr.x * 110.0, -1.0, 1.0)  // the slab sits at a different level
+       + 0.009 * clamp(fr.y * 110.0, -1.0, 1.0); // on each side of a crack
+}
+void main() {
+  vec2 screen = gl_FragCoord.xy / u_res;
+  vec2 p = (gl_FragCoord.xy - 0.5 * u_res) / u_res.y;
+  vec2 look = clamp(u_mouse - 0.5, -0.35, 0.35); // orbiting the slab centre
+  vec3 ray = normalize(vec3(p - look * 2.2, -1.6));
+
+  // Front surface along the view ray; two fixed-point steps settle on the swell.
+  float t = FRONT / ray.z;
+  for (int i = 0; i < 2; i++) t = (FRONT + height(ray.xy * t)) / ray.z;
+  vec3 hit = ray * t;
+
+  float e = 0.008;
+  vec2 slope = vec2(height(hit.xy + vec2(e, 0.0)) - height(hit.xy - vec2(e, 0.0)),
+                    height(hit.xy + vec2(0.0, e)) - height(hit.xy - vec2(0.0, e))) / (2.0 * e);
+  float bevel = smoothstep(0.14, 0.0, min(min(screen.x, 1.0 - screen.x), min(screen.y, 1.0 - screen.y)));
+  slope += bevel * (screen - 0.5) * 0.55; // the slab turns away at the frame edge
+  // The cracks are steps in the surface, so their slope flips sign within a pixel.
+  // That is what tears the plasma beautifully, and what would slice a fish to bits,
+  // so the fish are bent by the smooth swell alone.
+  vec2 slopeSmooth = vec2(heightSmooth(hit.xy + vec2(e, 0.0)) - heightSmooth(hit.xy - vec2(e, 0.0)),
+                          heightSmooth(hit.xy + vec2(0.0, e)) - heightSmooth(hit.xy - vec2(0.0, e))) / (2.0 * e);
+  vec3 normal = normalize(vec3(-slope, 1.0));
+  vec3 normalSmooth = normalize(vec3(-slopeSmooth, 1.0));
+  float facing = max(dot(-ray, normal), 0.0);
+
+  // Refracted ray; red and blue bend a little differently, which is what makes ice ring.
+  vec3 inside = refract(ray, normal, 1.0 / IOR);
+  vec2 shearR = (refract(ray, normal, 1.0 / (IOR - 0.012)) - inside).xy;
+  vec2 shearB = (refract(ray, normal, 1.0 / (IOR + 0.019)) - inside).xy;
+  inside = normalize(inside);
+  inside.z = min(inside.z, -0.40); // bound grazing rays at the crack steps
+
+  // Recentre the parallax on the middle of the sheet stack: near and far sheets
+  // then slide past each other at different rates as the pointer moves.
+  vec2 par = look * 4.54;
+
+  vec3 acc = vec3(0.0);
+  float trans = 1.0;
+  for (int i = 0; i < 8; i++) {
+    float layer = float(i);
+    bool solid = layer == 0.0 || layer == 1.0; // the two sheets that hold fish
+    float depth = solid ? 0.42 + layer * 0.26
+                        : texture2D(u_scene, atlasUV(hit.xy + par, layer)).a * 2.6;
+    float path = (hit.z - (FRONT - depth)) / -inside.z;                     // ice crossed to reach this sheet
+    // The slab is seen at a wide angle: the sheets themselves stretch up to four times
+    // towards the frame edges, which a fish silhouette cannot hide. So the fish ride
+    // on screen space and the ice bends them through its own slope instead.
+    vec2 at = solid ? (screen - 0.5) * 2.0 * EXTENT + normalSmooth.xy * path * 1.8 + par * 0.6
+                    : (hit + inside * path).xy + par;
+    vec3 plasma;
+    plasma.r = texture2D(u_scene, atlasUV(at + shearR * path, layer)).r;
+    plasma.g = texture2D(u_scene, atlasUV(at, layer)).g;
+    plasma.b = texture2D(u_scene, atlasUV(at + shearB * path, layer)).b;
+    vec3 c = plasma * exp(-SIGMA * path);
+    // Near plumes are nearly opaque, so the sheets behind them show through the gaps
+    // instead of averaging into a wash. That is what makes the stack read as depth.
+    // The shard is a solid, so its coverage comes straight from pass 1.
+    float alpha = solid ? texture2D(u_scene, atlasUV(at, layer)).a * 0.92
+                        : clamp(max(max(c.r, c.g), c.b) * 1.8, 0.0, 0.80);
+    acc += trans * c;
+    trans *= 1.0 - alpha;
+  }
+
+  // Gentle shoulder: overlapping glow stays coloured instead of clipping to white.
+  vec3 col = vec3(1.0) - exp(-acc * 1.5);
+
+  // Glass: reflection and a rim only where the surface turns away. Empty space stays dark.
+  float fresnel = pow(1.0 - facing, 5.0);
+  vec3 sky = mix(vec3(0.004, 0.016, 0.030), vec3(0.075, 0.220, 0.320), normal.y * 0.5 + 0.5);
+  col += sky * (fresnel * 1.2 + bevel * 0.03);
+  // Steep faces of the crests catch a thin sheen: the edge of the frozen surface,
+  // painted only where the ice actually tilts, so the open water stays black.
+  // Only the crack walls are this steep, so this sheen outlines the seams alone
+  // instead of washing the whole grain.
+  float tilt = smoothstep(1.00, 2.60, length(slope));
+  col += vec3(0.022, 0.062, 0.078) * tilt;
+  vec2 fr = fracture(hit.xy);
+  float crack = (1.0 - smoothstep(0.0, 0.004, abs(fr.x)))
+              + (1.0 - smoothstep(0.0, 0.004, abs(fr.y)));
+  col += vec3(0.020, 0.055, 0.068) * crack * smoothstep(0.58, 0.80, fbm2(hit.xy * 0.30 + 21.0));
+
+  gl_FragColor = vec4(pow(clamp(col, 0.0, 1.0), vec3(0.4545)), 1.0);
+}
diff --git a/debug_fish.frag b/debug_fish.frag
new file mode 100644
index 0000000..7a8ffcd
--- /dev/null
+++ b/debug_fish.frag
@@ -0,0 +1,61 @@
+// Debug view: the fish silhouette alone, on flat grey, big enough to judge the
+// geometry. Not part of the pages; build with
+//   python3 build_plasma.py 6_ice_plasma.frag debug_fish.frag debug_fish.html
+precision highp float;
+uniform vec2 u_res;
+uniform float u_time;
+
+float hash(vec2 p) { return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }
+float smin(float a, float b, float k) {
+  float h = clamp(0.5 + 0.5 * (b - a) / k, 0.0, 1.0);
+  return mix(b, a, h) - k * h * (1.0 - h);
+}
+float sdCapsule(vec2 p, vec2 a, vec2 b, float r) {
+  vec2 pa = p - a, ba = b - a;
+  float h = clamp(dot(pa, ba) / dot(ba, ba), 0.0, 1.0);
+  return length(pa - ba * h) - r;
+}
+float sdTriangle(vec2 p, vec2 p0, vec2 p1, vec2 p2) {
+  vec2 e0 = p1 - p0, e1 = p2 - p1, e2 = p0 - p2;
+  vec2 v0 = p - p0, v1 = p - p1, v2 = p - p2;
+  vec2 q0 = v0 - e0 * clamp(dot(v0, e0) / dot(e0, e0), 0.0, 1.0);
+  vec2 q1 = v1 - e1 * clamp(dot(v1, e1) / dot(e1, e1), 0.0, 1.0);
+  vec2 q2 = v2 - e2 * clamp(dot(v2, e2) / dot(e2, e2), 0.0, 1.0);
+  float s = sign(e0.x * e2.y - e0.y * e2.x);
+  vec2 d = min(min(vec2(dot(q0, q0), s * (v0.x * e0.y - v0.y * e0.x)),
+                   vec2(dot(q1, q1), s * (v1.x * e1.y - v1.y * e1.x))),
+                   vec2(dot(q2, q2), s * (v2.x * e2.y - v2.y * e2.x)));
+  return -sqrt(d.x) * sign(d.y);
+}
+// Half-height of the outline at x: pointed nose, deepest just behind the head,
+// a narrow peduncle, then the tail fan opening toward the rear. One function, so
+// the whole animal is guaranteed to be one connected shape.
+// Half-height of the body at x: pointed nose, deepest a quarter of the way back,
+// then down to a narrow peduncle. Sweeping a circle along it keeps the body one piece.
+float fishWidth(float x) {
+  float t = clamp((1.15 - x) / 2.30, 0.0, 1.0);        // 0 at the nose, 1 at the peduncle
+  return 0.34 * pow(sin(3.14159 * pow(t, 0.55)), 0.8) + 0.05 * smoothstep(0.70, 1.0, t);
+}
+float sdFish(vec2 p) {
+  float d = length(vec2(max(abs(p.x) - 1.15, 0.0), p.y)) - fishWidth(p.x);      // body
+  // tail: two lobes fanning back from the peduncle, with a notch between them
+  d = smin(d, sdTriangle(p, vec2(-1.02, 0.03), vec2(-1.62, 0.09), vec2(-1.46, 0.52)), 0.08);
+  d = smin(d, sdTriangle(p, vec2(-1.02, -0.03), vec2(-1.62, -0.09), vec2(-1.46, -0.52)), 0.08);
+  // dorsal and pectoral fins
+  d = smin(d, sdTriangle(p, vec2(0.22, 0.20), vec2(-0.06, 0.46), vec2(-0.40, 0.16)), 0.05);
+  d = smin(d, sdTriangle(p, vec2(0.46, -0.16), vec2(0.26, -0.08), vec2(0.10, -0.28)), 0.04);
+  return d;
+}
+
+void main() {
+  vec2 p = (gl_FragCoord.xy - 0.5 * u_res) / u_res.y * 3.0;
+  vec3 col = vec3(0.16, 0.17, 0.18);
+  for (int i = 0; i < 3; i++) {
+    float id = float(i);
+    float size = mix(1.15, 0.28, id / 2.0);
+    vec2 at = vec2(0.0, 0.75 - 0.72 * id);
+    float d = sdFish((p - at) / size);
+    col = mix(col, vec3(0.01), clamp(0.5 - d / (0.005 / size), 0.0, 1.0));
+  }
+  gl_FragColor = vec4(col, 1.0);
+}
diff --git a/debug_fish.html b/debug_fish.html
new file mode 100644
index 0000000..7208324
--- /dev/null
+++ b/debug_fish.html
@@ -0,0 +1,112 @@
+<!doctype html>
+<html lang="ru">
+<head>
+<meta charset="utf-8">
+<meta name="viewport" content="width=device-width,initial-scale=1">
+<title>Сквозь лёд</title>
+<style>
+html,body{margin:0;width:100%;height:100%;overflow:hidden;background:#03111d}
+canvas{display:block;width:100%;height:100%;touch-action:none}
+#info{position:fixed;bottom:20px;left:24px;color:#d8f4ff;font:13px/1.6 system-ui,sans-serif;text-shadow:0 1px 5px #001;pointer-events:none}
+#info strong{font-weight:500} #info span{opacity:.75}
+</style>
+</head>
+<body>
+<canvas id="view" aria-label="Плазма под прозрачным льдом. Двигайте указатель для параллакса."></canvas>
+<div id="info" role="status"><strong>Сквозь лёд</strong><br><span id="help">Двигайте мышь · скорость − / =</span></div>
+<script>
+'use strict';
+const sceneSource = "// Pass 1: eight plasma sheets, one atlas tile each. Alpha stores linear depth.\n// Density field lit as a height surface: billowing volumes with a real terminator.\nprecision highp float;\nuniform vec2 u_res; // size of one tile\nuniform float u_time;\n\nfloat hash(vec2 p) { return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }\nfloat noise(vec2 p) {\n  vec2 i = floor(p), f = fract(p);\n  f = f*f*(3.0-2.0*f);\n  return mix(mix(hash(i), hash(i+vec2(1.0,0.0)), f.x),\n             mix(hash(i+vec2(0.0,1.0)), hash(i+vec2(1.0,1.0)), f.x), f.y);\n}\nfloat fbm(vec2 p) {\n  float sum = 0.0, amp = 0.5;\n  for (int i = 0; i < 4; i++) {\n    sum += amp * noise(p);\n    p = mat2(1.62, 1.17, -1.17, 1.62) * p;\n    amp *= 0.5;\n  }\n  return sum;\n}\nfloat fbm2(vec2 p) {\n  return 0.5 * noise(p) + 0.25 * noise(mat2(1.62, 1.17, -1.17, 1.62) * p);\n}\nconst float EXTENT = 3.8; // half-width of a sheet in world units; must match the ice pass\n\nvoid main() {\n  vec2 tile = floor(gl_FragCoord.xy / u_res);\n  float layer = tile.x + tile.y * 4.0;\n  vec2 uv = fract(gl_FragCoord.xy / u_res);\n  vec2 p = (uv - 0.5) * 2.0 * vec2(EXTENT * u_res.x / u_res.y, EXTENT);\n  p *= 0.85 + 0.10 * layer; // far sheets carry finer detail, which reads as distance\n  float angle = hash(vec2(layer, 3.1)) * 6.2831853;\n  p = mat2(cos(angle), sin(angle), -sin(angle), cos(angle)) * p;\n\n  // Periodic time: every field returns exactly after 30 seconds.\n  float phase = u_time * 6.2831853 / 30.0;\n  vec2 o = vec2(cos(phase), sin(phase));\n  vec2 seed = vec2(layer * 17.3, layer * 9.1);\n\n  // Two nested warp stages, the marbled-plasma motion.\n  vec2 q = vec2(fbm(p * 0.50 + seed + o * 0.55),\n                fbm(p * 0.50 + seed + 23.1 - o * 0.55));\n  vec2 r = vec2(fbm(p * 0.85 + 2.0 * q + seed + vec2(o.y, -o.x) * 0.40),\n                fbm(p * 0.85 + 2.0 * q + seed + 31.7 - vec2(o.y, -o.x) * 0.40));\n  vec2 w = p * 1.10 + 2.6 * r + seed;   // warped coords of the density field\n\n  // The silhouette is shared by all sheets (slid a little per depth), so the gaps\n  // stay open right through the stack instead of filling in with overlap.\n  float mass = smoothstep(0.520, 0.548, fbm((p + o * 0.30 + vec2(0.10, -0.07) * layer) * 0.62 + r * 1.1 + 13.7));\n\n  // Light the density as a height surface: $cheap 2-octave gradient, strong terminator.\n  float h = 0.05;\n  vec2 slope = vec2(fbm2(w + vec2(h, 0.0)) - fbm2(w - vec2(h, 0.0)),\n                    fbm2(w + vec2(0.0, h)) - fbm2(w - vec2(0.0, h))) * (10.0 / (2.0 * h));\n  vec3 nrm = normalize(vec3(-slope, 1.0));\n  float lit = clamp(dot(nrm, normalize(vec3(-0.38, 0.52, 0.76))), 0.0, 1.0);\n\n  // Folded planes across the volume, feathered so they never read as a grid.\n  vec2 g = (p + r * 2.0) * 1.4;\n  vec2 cell = floor(g), f = fract(g);\n  float feather = smoothstep(0.0, 0.10, min(min(f.x, 1.0 - f.x), min(f.y, 1.0 - f.y)));\n  float facet = mix(1.0, mix(0.70, 1.25, hash(cell + seed + step(1.0, f.x + f.y) * 37.0)), feather);\n\n  float shade = 0.05 + 1.10 * lit * lit;                // lit tops, near-black undersides\n  float e = mass * facet * shade * 0.085\n          + mass * (1.0 - mass) * 4.0 * 0.040           // thin torn silhouette\n          + mass * pow(lit, 14.0) * 0.110;              // glint where a fold faces the light\n  vec3 col = e * mix(vec3(0.02, 0.42, 0.60), vec3(0.08, 0.64, 0.88), facet * 0.5);\n  // Faint dye in the open gaps so darkness reads as depth, not as a hole.\n  col += smoothstep(0.40, 0.85, fbm(p * 0.30 + seed * 0.4 + o * 0.3)) * vec3(0.0003, 0.0011, 0.0015);\n\n  gl_FragColor = vec4(col, (0.42 + layer * 0.26) / 2.6);\n}\n";
+const iceSource = "// Debug view: the fish silhouette alone, on flat grey, big enough to judge the\n// geometry. Not part of the pages; build with\n//   python3 build_plasma.py 6_ice_plasma.frag debug_fish.frag debug_fish.html\nprecision highp float;\nuniform vec2 u_res;\nuniform float u_time;\n\nfloat hash(vec2 p) { return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }\nfloat smin(float a, float b, float k) {\n  float h = clamp(0.5 + 0.5 * (b - a) / k, 0.0, 1.0);\n  return mix(b, a, h) - k * h * (1.0 - h);\n}\nfloat sdCapsule(vec2 p, vec2 a, vec2 b, float r) {\n  vec2 pa = p - a, ba = b - a;\n  float h = clamp(dot(pa, ba) / dot(ba, ba), 0.0, 1.0);\n  return length(pa - ba * h) - r;\n}\nfloat sdTriangle(vec2 p, vec2 p0, vec2 p1, vec2 p2) {\n  vec2 e0 = p1 - p0, e1 = p2 - p1, e2 = p0 - p2;\n  vec2 v0 = p - p0, v1 = p - p1, v2 = p - p2;\n  vec2 q0 = v0 - e0 * clamp(dot(v0, e0) / dot(e0, e0), 0.0, 1.0);\n  vec2 q1 = v1 - e1 * clamp(dot(v1, e1) / dot(e1, e1), 0.0, 1.0);\n  vec2 q2 = v2 - e2 * clamp(dot(v2, e2) / dot(e2, e2), 0.0, 1.0);\n  float s = sign(e0.x * e2.y - e0.y * e2.x);\n  vec2 d = min(min(vec2(dot(q0, q0), s * (v0.x * e0.y - v0.y * e0.x)),\n                   vec2(dot(q1, q1), s * (v1.x * e1.y - v1.y * e1.x))),\n                   vec2(dot(q2, q2), s * (v2.x * e2.y - v2.y * e2.x)));\n  return -sqrt(d.x) * sign(d.y);\n}\n// Half-height of the outline at x: pointed nose, deepest just behind the head,\n// a narrow peduncle, then the tail fan opening toward the rear. One function, so\n// the whole animal is guaranteed to be one connected shape.\n// Half-height of the body at x: pointed nose, deepest a quarter of the way back,\n// then down to a narrow peduncle. Sweeping a circle along it keeps the body one piece.\nfloat fishWidth(float x) {\n  float t = clamp((1.15 - x) / 2.30, 0.0, 1.0);        // 0 at the nose, 1 at the peduncle\n  return 0.34 * pow(sin(3.14159 * pow(t, 0.55)), 0.8) + 0.05 * smoothstep(0.70, 1.0, t);\n}\nfloat sdFish(vec2 p) {\n  float d = length(vec2(max(abs(p.x) - 1.15, 0.0), p.y)) - fishWidth(p.x);      // body\n  // tail: two lobes fanning back from the peduncle, with a notch between them\n  d = smin(d, sdTriangle(p, vec2(-1.02, 0.03), vec2(-1.62, 0.09), vec2(-1.46, 0.52)), 0.08);\n  d = smin(d, sdTriangle(p, vec2(-1.02, -0.03), vec2(-1.62, -0.09), vec2(-1.46, -0.52)), 0.08);\n  // dorsal and pectoral fins\n  d = smin(d, sdTriangle(p, vec2(0.22, 0.20), vec2(-0.06, 0.46), vec2(-0.40, 0.16)), 0.05);\n  d = smin(d, sdTriangle(p, vec2(0.46, -0.16), vec2(0.26, -0.08), vec2(0.10, -0.28)), 0.04);\n  return d;\n}\n\nvoid main() {\n  vec2 p = (gl_FragCoord.xy - 0.5 * u_res) / u_res.y * 3.0;\n  vec3 col = vec3(0.16, 0.17, 0.18);\n  for (int i = 0; i < 3; i++) {\n    float id = float(i);\n    float size = mix(1.15, 0.28, id / 2.0);\n    vec2 at = vec2(0.0, 0.75 - 0.72 * id);\n    float d = sdFish((p - at) / size);\n    col = mix(col, vec3(0.01), clamp(0.5 - d / (0.005 / size), 0.0, 1.0));\n  }\n  gl_FragColor = vec4(col, 1.0);\n}\n";
+const vertexSource = 'attribute vec2 p; void main(){gl_Position=vec4(p,0.0,1.0);}';
+const canvas = document.getElementById('view'), help = document.getElementById('help');
+const gl = canvas.getContext('webgl', {antialias:false, alpha:false, preserveDrawingBuffer:true});
+function fail(message) { help.textContent = message; throw new Error(message); }
+if (!gl) fail('WebGL недоступен в этом браузере.');
+function program(source) {
+  function shader(type, code) {
+    const s = gl.createShader(type);
+    gl.shaderSource(s, code); gl.compileShader(s);
+    if (!gl.getShaderParameter(s, gl.COMPILE_STATUS)) fail('Ошибка шейдера: ' + gl.getShaderInfoLog(s));
+    return s;
+  }
+  const p = gl.createProgram(), vs = shader(gl.VERTEX_SHADER, vertexSource), fs = shader(gl.FRAGMENT_SHADER, source);
+  gl.attachShader(p, vs); gl.attachShader(p, fs); gl.linkProgram(p);
+  gl.deleteShader(vs); gl.deleteShader(fs);
+  if (!gl.getProgramParameter(p, gl.LINK_STATUS)) fail('Ошибка программы: ' + gl.getProgramInfoLog(p));
+  return p;
+}
+const scene = program(sceneSource), ice = program(iceSource);
+const buffer = gl.createBuffer();
+gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
+gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([-1,-1,1,-1,-1,1,1,1]), gl.STATIC_DRAW);
+let texture, framebuffer, tileWidth, tileHeight;
+function resize() {
+  const max = gl.getParameter(gl.MAX_TEXTURE_SIZE);
+  const dpr = Math.min(devicePixelRatio || 1, 1.25, max / (innerWidth * 3), max / (innerHeight * 1.5));
+  canvas.width = Math.max(4, Math.floor(innerWidth * dpr / 4) * 4);
+  canvas.height = Math.max(4, Math.floor(innerHeight * dpr / 4) * 4);
+  tileWidth = canvas.width * 3 / 4; tileHeight = canvas.height * 3 / 4;
+  if (texture) gl.deleteTexture(texture);
+  if (framebuffer) gl.deleteFramebuffer(framebuffer);
+  texture = gl.createTexture(); gl.bindTexture(gl.TEXTURE_2D, texture);
+  gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, tileWidth * 4, tileHeight * 2, 0, gl.RGBA, gl.UNSIGNED_BYTE, null);
+  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
+  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
+  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
+  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
+  framebuffer = gl.createFramebuffer(); gl.bindFramebuffer(gl.FRAMEBUFFER, framebuffer);
+  gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, texture, 0);
+  if (gl.checkFramebufferStatus(gl.FRAMEBUFFER) !== gl.FRAMEBUFFER_COMPLETE) fail('Не удалось создать текстуру сцены.');
+  gl.bindFramebuffer(gl.FRAMEBUFFER, null);
+}
+addEventListener('resize', resize); resize();
+const shot = location.hash.startsWith('#shot');
+const shotParams = new URLSearchParams(location.hash.slice(1));
+let mouseX = Number(shotParams.get('mx') ?? 0.5), mouseY = Number(shotParams.get('my') ?? 0.5);
+let speed = 1, time = Number(shotParams.get('t') ?? 0), previous;
+addEventListener('pointermove', e => { mouseX = e.clientX / innerWidth; mouseY = 1 - e.clientY / innerHeight; });
+addEventListener('keydown', e => {
+  if (e.key === '-' || e.key === '_') speed = Math.max(0.125, speed / 2);
+  else if (e.key === '=' || e.key === '+') speed = Math.min(4, speed * 2);
+  else return;
+  help.textContent = 'Двигайте мышь · скорость ' + speed + '×  (− / =)';
+});
+function draw(p, width, height) {
+  gl.useProgram(p);
+  const position = gl.getAttribLocation(p, 'p');
+  gl.bindBuffer(gl.ARRAY_BUFFER, buffer); gl.enableVertexAttribArray(position);
+  gl.vertexAttribPointer(position, 2, gl.FLOAT, false, 0, 0);
+  gl.uniform2f(gl.getUniformLocation(p, 'u_res'), width, height);
+  gl.uniform1f(gl.getUniformLocation(p, 'u_time'), time);
+  gl.uniform2f(gl.getUniformLocation(p, 'u_mouse'), mouseX, mouseY);
+  gl.uniform2f(gl.getUniformLocation(p, 'u_tile_res'), tileWidth, tileHeight);
+  gl.uniform1i(gl.getUniformLocation(p, 'u_scene'), 0);
+  gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);
+}
+function frame(now) {
+  if (previous !== undefined) time += (now - previous) * 0.001 * speed;
+  previous = now;
+  gl.bindFramebuffer(gl.FRAMEBUFFER, framebuffer);
+  gl.viewport(0, 0, tileWidth * 4, tileHeight * 2);
+  draw(scene, tileWidth, tileHeight);
+  gl.bindFramebuffer(gl.FRAMEBUFFER, null);
+  gl.viewport(0, 0, canvas.width, canvas.height);
+  gl.activeTexture(gl.TEXTURE0); gl.bindTexture(gl.TEXTURE_2D, texture);
+  draw(ice, canvas.width, canvas.height);
+  if (shot) {
+    // Headless Firefox does not composite WebGL; expose the actual rendered pixels.
+    const pixels = new Uint8Array(canvas.width * canvas.height * 4);
+    gl.readPixels(0, 0, canvas.width, canvas.height, gl.RGBA, gl.UNSIGNED_BYTE, pixels);
+    const output = document.createElement('canvas');
+    output.width = canvas.width; output.height = canvas.height;
+    const ctx = output.getContext('2d'), image = ctx.createImageData(output.width, output.height);
+    for (let y = 0; y < output.height; y++)
+      image.data.set(pixels.subarray((output.height - y - 1) * output.width * 4, (output.height - y) * output.width * 4), y * output.width * 4);
+    ctx.putImageData(image, 0, 0); canvas.replaceWith(output);
+  } else requestAnimationFrame(frame);
+}
+if (shot) frame(0); else requestAnimationFrame(frame);
+</script>
+</body>
+</html>
diff --git a/ice_fish.html b/ice_fish.html
new file mode 100644
index 0000000..d5074bb
--- /dev/null
+++ b/ice_fish.html
@@ -0,0 +1,112 @@
+<!doctype html>
+<html lang="ru">
+<head>
+<meta charset="utf-8">
+<meta name="viewport" content="width=device-width,initial-scale=1">
+<title>Сквозь лёд</title>
+<style>
+html,body{margin:0;width:100%;height:100%;overflow:hidden;background:#03111d}
+canvas{display:block;width:100%;height:100%;touch-action:none}
+#info{position:fixed;bottom:20px;left:24px;color:#d8f4ff;font:13px/1.6 system-ui,sans-serif;text-shadow:0 1px 5px #001;pointer-events:none}
+#info strong{font-weight:500} #info span{opacity:.75}
+</style>
+</head>
+<body>
+<canvas id="view" aria-label="Плазма под прозрачным льдом. Двигайте указатель для параллакса."></canvas>
+<div id="info" role="status"><strong>Сквозь лёд</strong><br><span id="help">Двигайте мышь · скорость − / =</span></div>
+<script>
+'use strict';
+const sceneSource = "// Pass 1: eight plasma sheets, one atlas tile each. Alpha stores linear depth,\n// except on the three sheets that carry the fish: there it stores how much of the\n// pixel the fish covers, so the ice pass can draw them as solid dark shapes.\n// Density field lit as a height surface: billowing volumes with a real terminator.\nprecision highp float;\nuniform vec2 u_res; // size of one tile\nuniform float u_time;\n\nfloat hash(vec2 p) { return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }\nfloat noise(vec2 p) {\n  vec2 i = floor(p), f = fract(p);\n  f = f*f*(3.0-2.0*f);\n  return mix(mix(hash(i), hash(i+vec2(1.0,0.0)), f.x),\n             mix(hash(i+vec2(0.0,1.0)), hash(i+vec2(1.0,1.0)), f.x), f.y);\n}\nfloat fbm(vec2 p) {\n  float sum = 0.0, amp = 0.5;\n  for (int i = 0; i < 4; i++) {\n    sum += amp * noise(p);\n    p = mat2(1.62, 1.17, -1.17, 1.62) * p;\n    amp *= 0.5;\n  }\n  return sum;\n}\nfloat fbm2(vec2 p) {\n  return 0.5 * noise(p) + 0.25 * noise(mat2(1.62, 1.17, -1.17, 1.62) * p);\n}\n\n// Silhouette of a fish: pointed nose, deepest just behind the head, a narrow\n// peduncle, then a tail fan with a fork cut out of it. One width function, so the\n// whole animal is guaranteed to be a single connected shape.\nfloat smin(float a, float b, float k) {\n  float h = clamp(0.5 + 0.5 * (b - a) / k, 0.0, 1.0);\n  return mix(b, a, h) - k * h * (1.0 - h);\n}\nfloat sdTriangle(vec2 p, vec2 p0, vec2 p1, vec2 p2) {\n  vec2 e0 = p1 - p0, e1 = p2 - p1, e2 = p0 - p2;\n  vec2 v0 = p - p0, v1 = p - p1, v2 = p - p2;\n  vec2 q0 = v0 - e0 * clamp(dot(v0, e0) / dot(e0, e0), 0.0, 1.0);\n  vec2 q1 = v1 - e1 * clamp(dot(v1, e1) / dot(e1, e1), 0.0, 1.0);\n  vec2 q2 = v2 - e2 * clamp(dot(v2, e2) / dot(e2, e2), 0.0, 1.0);\n  float s = sign(e0.x * e2.y - e0.y * e2.x);\n  vec2 d = min(min(vec2(dot(q0, q0), s * (v0.x * e0.y - v0.y * e0.x)),\n                   vec2(dot(q1, q1), s * (v1.x * e1.y - v1.y * e1.x))),\n                   vec2(dot(q2, q2), s * (v2.x * e2.y - v2.y * e2.x)));\n  return -sqrt(d.x) * sign(d.y);\n}\n// Half-height of the body at x: pointed nose, deepest a quarter of the way back,\n// then down to a narrow peduncle. Sweeping a circle along it keeps the body one piece.\nfloat fishWidth(float x) {\n  float t = clamp((1.15 - x) / 2.30, 0.0, 1.0);        // 0 at the nose, 1 at the peduncle\n  return 0.34 * pow(sin(3.14159 * pow(t, 0.55)), 0.8) + 0.05 * smoothstep(0.70, 1.0, t);\n}\nfloat sdFish(vec2 p) {\n  float d = length(vec2(max(abs(p.x) - 1.15, 0.0), p.y)) - fishWidth(p.x);      // body\n  // tail: two lobes fanning back from the peduncle, with a notch between them\n  d = smin(d, sdTriangle(p, vec2(-1.02, 0.03), vec2(-1.62, 0.09), vec2(-1.46, 0.52)), 0.08);\n  d = smin(d, sdTriangle(p, vec2(-1.02, -0.03), vec2(-1.62, -0.09), vec2(-1.46, -0.52)), 0.08);\n  // dorsal and pectoral fins\n  d = smin(d, sdTriangle(p, vec2(0.22, 0.20), vec2(-0.06, 0.46), vec2(-0.40, 0.16)), 0.05);\n  d = smin(d, sdTriangle(p, vec2(0.46, -0.16), vec2(0.26, -0.08), vec2(0.10, -0.28)), 0.04);\n  return d;\n}\n\nconst float EXTENT = 3.8; // half-width of a sheet in world units; must match the ice pass\n\nvoid main() {\n  vec2 tile = floor(gl_FragCoord.xy / u_res);\n  float layer = tile.x + tile.y * 4.0;\n  vec2 uv = fract(gl_FragCoord.xy / u_res);\n  vec2 p = (uv - 0.5) * 2.0 * vec2(EXTENT * u_res.x / u_res.y, EXTENT);\n  p *= 0.85 + 0.10 * layer; // far sheets carry finer detail, which reads as distance\n  float angle = hash(vec2(layer, 3.1)) * 6.2831853;\n  p = mat2(cos(angle), sin(angle), -sin(angle), cos(angle)) * p;\n\n  // Periodic time: every field returns exactly after 30 seconds.\n  float phase = u_time * 6.2831853 / 30.0;\n  vec2 o = vec2(cos(phase), sin(phase));\n  vec2 seed = vec2(layer * 17.3, layer * 9.1);\n\n  // Two nested warp stages, the marbled-plasma motion.\n  vec2 q = vec2(fbm(p * 0.50 + seed + o * 0.55),\n                fbm(p * 0.50 + seed + 23.1 - o * 0.55));\n  vec2 r = vec2(fbm(p * 0.85 + 2.0 * q + seed + vec2(o.y, -o.x) * 0.40),\n                fbm(p * 0.85 + 2.0 * q + seed + 31.7 - vec2(o.y, -o.x) * 0.40));\n  vec2 w = p * 1.10 + 2.6 * r + seed;   // warped coords of the density field\n\n  // The silhouette is shared by all sheets (slid a little per depth), so the gaps\n  // stay open right through the stack instead of filling in with overlap.\n  float mass = smoothstep(0.520, 0.548, fbm((p + o * 0.30 + vec2(0.10, -0.07) * layer) * 0.62 + r * 1.1 + 13.7));\n\n  // Light the density as a height surface: $cheap 2-octave gradient, strong terminator.\n  float h = 0.05;\n  vec2 slope = vec2(fbm2(w + vec2(h, 0.0)) - fbm2(w - vec2(h, 0.0)),\n                    fbm2(w + vec2(0.0, h)) - fbm2(w - vec2(0.0, h))) * (10.0 / (2.0 * h));\n  vec3 nrm = normalize(vec3(-slope, 1.0));\n  float lit = clamp(dot(nrm, normalize(vec3(-0.38, 0.52, 0.76))), 0.0, 1.0);\n\n  // Folded planes across the volume, feathered so they never read as a grid.\n  vec2 g = (p + r * 2.0) * 1.4;\n  vec2 cell = floor(g), f = fract(g);\n  float feather = smoothstep(0.0, 0.10, min(min(f.x, 1.0 - f.x), min(f.y, 1.0 - f.y)));\n  float facet = mix(1.0, mix(0.70, 1.25, hash(cell + seed + step(1.0, f.x + f.y) * 37.0)), feather);\n\n  float shade = 0.05 + 1.10 * lit * lit;                // lit tops, near-black undersides\n  float e = mass * facet * shade * 0.085\n          + mass * (1.0 - mass) * 4.0 * 0.040           // thin torn silhouette\n          + mass * pow(lit, 14.0) * 0.110;              // glint where a fold faces the light\n  vec3 col = e * mix(vec3(0.02, 0.42, 0.60), vec3(0.08, 0.64, 0.88), facet * 0.5);\n  // Faint dye in the open gaps so darkness reads as depth, not as a hole.\n  col += smoothstep(0.40, 0.85, fbm(p * 0.30 + seed * 0.4 + o * 0.3)) * vec3(0.0003, 0.0011, 0.0015);\n\n\n  // Two sheets carry fish. Each one cuts straight across the slab once per cycle,\n  // with long gaps and a wide spread of sizes: mostly small, now and then something\n  // far too big. They are almost pure black, so all you ever see is the silhouette\n  // eating into the glow behind them, bent by the cracks in the ice.\n  float cover = (0.42 + layer * 0.26) / 2.6; // the sheet's own opacity, except where a fish is\n  if (layer == 0.0 || layer == 1.0) {\n    vec2 sp = (uv - 0.5) * 2.0 * vec2(EXTENT * u_res.x / u_res.y, EXTENT);\n    float t01 = u_time / 30.0;\n    for (int k = 0; k < 2; k++) {\n      float id = float(k);\n      float lt = fract(t01 + hash(vec2(layer, id)));\n      if (lt < 0.02 || lt > 0.98) continue;\n      float dir = hash(vec2(id, layer + 5.0)) > 0.5 ? 1.0 : -1.0;\n      float y0 = (hash(vec2(id, layer + 13.0)) - 0.5) * 4.6;\n      float y1 = y0 + (hash(vec2(id, layer + 17.0)) - 0.5) * 1.8;\n      vec2 pos = mix(vec2(-dir * 8.6, y0), vec2(dir * 8.6, y1), lt);\n      float tilt = atan((y1 - y0) / 17.2);\n      float size = 0.30 + 1.30 * pow(hash(vec2(id, layer + 3.0)), 2.2);\n      vec2 q = (mat2(cos(tilt), -sin(tilt), sin(tilt), cos(tilt)) * (sp - pos) * vec2(dir, 1.0)) / size;\n      float d = sdFish(q);\n      float px = 0.019 / size;\n      float cov = clamp(0.5 - d / px, 0.0, 1.0);\n      if (cov >= 0.0) {\n        // A dark body, a faint halo where the ice is lit around it, and two small\n        // eyes that burn cold blue: that is the only thing that says \"alive\".\n        float halo = max(clamp(0.5 - (d - 0.16) / (px * 6.0), 0.0, 1.0) - cov, 0.0);\n        col += vec3(0.006, 0.020, 0.032) * halo;\n        if (cov > 0.0) {\n          col = mix(col, vec3(0.0010, 0.0014, 0.0018), cov);\n          float eye = smoothstep(0.045, 0.012, length(q - vec2(0.80, 0.095)));\n          eye += 0.22 * smoothstep(0.11, 0.0, length(q - vec2(0.80, 0.095)));\n          eye += 0.07 * smoothstep(0.26, 0.0, length(q - vec2(0.76, 0.05))); // the head catches it\n          col += vec3(0.06, 0.44, 0.80) * eye * cov;\n          cover = 1.0;\n        }\n      }\n    }\n  }\n  float alpha = (layer == 0.0 || layer == 1.0) ? cover : (0.42 + layer * 0.26) / 2.6;\n  gl_FragColor = vec4(col, alpha);\n}\n";
+const iceSource = "// Pass 2: clean ice. Refraction, chromatic shear, absorption by true path length.\n// Nothing is added to empty space, so the gaps between sheets stay black.\nprecision highp float;\nuniform vec2 u_res;\nuniform float u_time;\nuniform vec2 u_mouse; // normalized, bottom-left origin\nuniform sampler2D u_scene;\nuniform vec2 u_tile_res;\n\nconst float EXTENT = 3.8;                 // must match the plasma pass\nconst float FRONT  = -2.0;                // ice surface, camera at the origin looking down -z\nconst vec3  SIGMA  = vec3(0.66, 0.26, 0.11); // absorption per unit: red dies first, so depth turns blue\nconst float IOR    = 1.31;\n// The fish sheets store coverage in alpha, so their depth comes from the index.\n\nfloat hash(vec2 p) { return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }\nfloat noise(vec2 p) {\n  vec2 i = floor(p), f = fract(p);\n  f = f*f*(3.0-2.0*f);\n  return mix(mix(hash(i), hash(i+vec2(1.0,0.0)), f.x),\n             mix(hash(i+vec2(0.0,1.0)), hash(i+vec2(1.0,1.0)), f.x), f.y);\n}\nfloat fbm(vec2 p) {\n  float sum = 0.0, amp = 0.5;\n  for (int i = 0; i < 3; i++) { sum += amp * noise(p); p = mat2(1.62, 1.17, -1.17, 1.62) * p; amp *= 0.5; }\n  return sum;\n}\nfloat fbm2(vec2 p) {\n  return 0.5 * noise(p) + 0.25 * noise(mat2(1.62, 1.17, -1.17, 1.62) * p);\n}\nvec2 atlasUV(vec2 world, float layer) {\n  vec2 uv = world / (2.0 * EXTENT) + 0.5;\n  uv = clamp(uv, 0.5 / u_tile_res, 1.0 - 0.5 / u_tile_res); // keep bilinear taps inside the tile\n  return (vec2(mod(layer, 4.0), floor(layer / 4.0)) + uv) / vec2(4.0, 2.0);\n}\n// The slab's fracture lines: two families of long, slightly wandering cracks. Shared\n// by the height field and the sheen, so each crack is both a bright seam and a step.\nvec2 fracture(vec2 x) {\n  float d = fbm(x * 0.62 + 3.0) - 0.5;                 // zero set: long winding cracks\n  float e = fbm(x * 1.35 - 7.0) - 0.5;                 // a sparser second family\n  return vec2(d, e);\n}\n// Frozen surface: fine ridged grain over the plates the cracks have lifted apart.\n// Static in world space; only the plasma behind it moves.\nfloat heightSmooth(vec2 x) {\n  return 0.090 * (1.0 - abs(2.0 * fbm2(x * 2.2 + 2.0) - 1.0))\n       + 0.055 * (1.0 - abs(2.0 * fbm2(x * 6.4 - 5.0) - 1.0));\n}\nfloat height(vec2 x) {\n  vec2 fr = fracture(x);\n  return heightSmooth(x)\n       + 0.014 * clamp(fr.x * 110.0, -1.0, 1.0)  // the slab sits at a different level\n       + 0.009 * clamp(fr.y * 110.0, -1.0, 1.0); // on each side of a crack\n}\nvoid main() {\n  vec2 screen = gl_FragCoord.xy / u_res;\n  vec2 p = (gl_FragCoord.xy - 0.5 * u_res) / u_res.y;\n  vec2 look = clamp(u_mouse - 0.5, -0.35, 0.35); // orbiting the slab centre\n  vec3 ray = normalize(vec3(p - look * 2.2, -1.6));\n\n  // Front surface along the view ray; two fixed-point steps settle on the swell.\n  float t = FRONT / ray.z;\n  for (int i = 0; i < 2; i++) t = (FRONT + height(ray.xy * t)) / ray.z;\n  vec3 hit = ray * t;\n\n  float e = 0.008;\n  vec2 slope = vec2(height(hit.xy + vec2(e, 0.0)) - height(hit.xy - vec2(e, 0.0)),\n                    height(hit.xy + vec2(0.0, e)) - height(hit.xy - vec2(0.0, e))) / (2.0 * e);\n  float bevel = smoothstep(0.14, 0.0, min(min(screen.x, 1.0 - screen.x), min(screen.y, 1.0 - screen.y)));\n  slope += bevel * (screen - 0.5) * 0.55; // the slab turns away at the frame edge\n  // The cracks are steps in the surface, so their slope flips sign within a pixel.\n  // That is what tears the plasma beautifully, and what would slice a fish to bits,\n  // so the fish are bent by the smooth swell alone.\n  vec2 slopeSmooth = vec2(heightSmooth(hit.xy + vec2(e, 0.0)) - heightSmooth(hit.xy - vec2(e, 0.0)),\n                          heightSmooth(hit.xy + vec2(0.0, e)) - heightSmooth(hit.xy - vec2(0.0, e))) / (2.0 * e);\n  vec3 normal = normalize(vec3(-slope, 1.0));\n  vec3 normalSmooth = normalize(vec3(-slopeSmooth, 1.0));\n  float facing = max(dot(-ray, normal), 0.0);\n\n  // Refracted ray; red and blue bend a little differently, which is what makes ice ring.\n  vec3 inside = refract(ray, normal, 1.0 / IOR);\n  vec2 shearR = (refract(ray, normal, 1.0 / (IOR - 0.012)) - inside).xy;\n  vec2 shearB = (refract(ray, normal, 1.0 / (IOR + 0.019)) - inside).xy;\n  inside = normalize(inside);\n  inside.z = min(inside.z, -0.40); // bound grazing rays at the crack steps\n\n  // Recentre the parallax on the middle of the sheet stack: near and far sheets\n  // then slide past each other at different rates as the pointer moves.\n  vec2 par = look * 4.54;\n\n  vec3 acc = vec3(0.0);\n  float trans = 1.0;\n  for (int i = 0; i < 8; i++) {\n    float layer = float(i);\n    bool solid = layer == 0.0 || layer == 1.0; // the two sheets that hold fish\n    float depth = solid ? 0.42 + layer * 0.26\n                        : texture2D(u_scene, atlasUV(hit.xy + par, layer)).a * 2.6;\n    float path = (hit.z - (FRONT - depth)) / -inside.z;                     // ice crossed to reach this sheet\n    // The slab is seen at a wide angle: the sheets themselves stretch up to four times\n    // towards the frame edges, which a fish silhouette cannot hide. So the fish ride\n    // on screen space and the ice bends them through its own slope instead.\n    vec2 at = solid ? (screen - 0.5) * 2.0 * EXTENT + normalSmooth.xy * path * 1.8 + par * 0.6\n                    : (hit + inside * path).xy + par;\n    vec3 plasma;\n    plasma.r = texture2D(u_scene, atlasUV(at + shearR * path, layer)).r;\n    plasma.g = texture2D(u_scene, atlasUV(at, layer)).g;\n    plasma.b = texture2D(u_scene, atlasUV(at + shearB * path, layer)).b;\n    vec3 c = plasma * exp(-SIGMA * path);\n    // Near plumes are nearly opaque, so the sheets behind them show through the gaps\n    // instead of averaging into a wash. That is what makes the stack read as depth.\n    // The shard is a solid, so its coverage comes straight from pass 1.\n    float alpha = solid ? texture2D(u_scene, atlasUV(at, layer)).a * 0.92\n                        : clamp(max(max(c.r, c.g), c.b) * 1.8, 0.0, 0.80);\n    acc += trans * c;\n    trans *= 1.0 - alpha;\n  }\n\n  // Gentle shoulder: overlapping glow stays coloured instead of clipping to white.\n  vec3 col = vec3(1.0) - exp(-acc * 1.5);\n\n  // Glass: reflection and a rim only where the surface turns away. Empty space stays dark.\n  float fresnel = pow(1.0 - facing, 5.0);\n  vec3 sky = mix(vec3(0.004, 0.016, 0.030), vec3(0.075, 0.220, 0.320), normal.y * 0.5 + 0.5);\n  col += sky * (fresnel * 1.2 + bevel * 0.03);\n  // Steep faces of the crests catch a thin sheen: the edge of the frozen surface,\n  // painted only where the ice actually tilts, so the open water stays black.\n  // Only the crack walls are this steep, so this sheen outlines the seams alone\n  // instead of washing the whole grain.\n  float tilt = smoothstep(1.00, 2.60, length(slope));\n  col += vec3(0.022, 0.062, 0.078) * tilt;\n  vec2 fr = fracture(hit.xy);\n  float crack = (1.0 - smoothstep(0.0, 0.004, abs(fr.x)))\n              + (1.0 - smoothstep(0.0, 0.004, abs(fr.y)));\n  col += vec3(0.020, 0.055, 0.068) * crack * smoothstep(0.58, 0.80, fbm2(hit.xy * 0.30 + 21.0));\n\n  gl_FragColor = vec4(pow(clamp(col, 0.0, 1.0), vec3(0.4545)), 1.0);\n}\n";
+const vertexSource = 'attribute vec2 p; void main(){gl_Position=vec4(p,0.0,1.0);}';
+const canvas = document.getElementById('view'), help = document.getElementById('help');
+const gl = canvas.getContext('webgl', {antialias:false, alpha:false, preserveDrawingBuffer:true});
+function fail(message) { help.textContent = message; throw new Error(message); }
+if (!gl) fail('WebGL недоступен в этом браузере.');
+function program(source) {
+  function shader(type, code) {
+    const s = gl.createShader(type);
+    gl.shaderSource(s, code); gl.compileShader(s);
+    if (!gl.getShaderParameter(s, gl.COMPILE_STATUS)) fail('Ошибка шейдера: ' + gl.getShaderInfoLog(s));
+    return s;
+  }
+  const p = gl.createProgram(), vs = shader(gl.VERTEX_SHADER, vertexSource), fs = shader(gl.FRAGMENT_SHADER, source);
+  gl.attachShader(p, vs); gl.attachShader(p, fs); gl.linkProgram(p);
+  gl.deleteShader(vs); gl.deleteShader(fs);
+  if (!gl.getProgramParameter(p, gl.LINK_STATUS)) fail('Ошибка программы: ' + gl.getProgramInfoLog(p));
+  return p;
+}
+const scene = program(sceneSource), ice = program(iceSource);
+const buffer = gl.createBuffer();
+gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
+gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([-1,-1,1,-1,-1,1,1,1]), gl.STATIC_DRAW);
+let texture, framebuffer, tileWidth, tileHeight;
+function resize() {
+  const max = gl.getParameter(gl.MAX_TEXTURE_SIZE);
+  const dpr = Math.min(devicePixelRatio || 1, 1.25, max / (innerWidth * 3), max / (innerHeight * 1.5));
+  canvas.width = Math.max(4, Math.floor(innerWidth * dpr / 4) * 4);
+  canvas.height = Math.max(4, Math.floor(innerHeight * dpr / 4) * 4);
+  tileWidth = canvas.width * 3 / 4; tileHeight = canvas.height * 3 / 4;
+  if (texture) gl.deleteTexture(texture);
+  if (framebuffer) gl.deleteFramebuffer(framebuffer);
+  texture = gl.createTexture(); gl.bindTexture(gl.TEXTURE_2D, texture);
+  gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, tileWidth * 4, tileHeight * 2, 0, gl.RGBA, gl.UNSIGNED_BYTE, null);
+  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
+  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
+  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
+  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
+  framebuffer = gl.createFramebuffer(); gl.bindFramebuffer(gl.FRAMEBUFFER, framebuffer);
+  gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, texture, 0);
+  if (gl.checkFramebufferStatus(gl.FRAMEBUFFER) !== gl.FRAMEBUFFER_COMPLETE) fail('Не удалось создать текстуру сцены.');
+  gl.bindFramebuffer(gl.FRAMEBUFFER, null);
+}
+addEventListener('resize', resize); resize();
+const shot = location.hash.startsWith('#shot');
+const shotParams = new URLSearchParams(location.hash.slice(1));
+let mouseX = Number(shotParams.get('mx') ?? 0.5), mouseY = Number(shotParams.get('my') ?? 0.5);
+let speed = 1, time = Number(shotParams.get('t') ?? 0), previous;
+addEventListener('pointermove', e => { mouseX = e.clientX / innerWidth; mouseY = 1 - e.clientY / innerHeight; });
+addEventListener('keydown', e => {
+  if (e.key === '-' || e.key === '_') speed = Math.max(0.125, speed / 2);
+  else if (e.key === '=' || e.key === '+') speed = Math.min(4, speed * 2);
+  else return;
+  help.textContent = 'Двигайте мышь · скорость ' + speed + '×  (− / =)';
+});
+function draw(p, width, height) {
+  gl.useProgram(p);
+  const position = gl.getAttribLocation(p, 'p');
+  gl.bindBuffer(gl.ARRAY_BUFFER, buffer); gl.enableVertexAttribArray(position);
+  gl.vertexAttribPointer(position, 2, gl.FLOAT, false, 0, 0);
+  gl.uniform2f(gl.getUniformLocation(p, 'u_res'), width, height);
+  gl.uniform1f(gl.getUniformLocation(p, 'u_time'), time);
+  gl.uniform2f(gl.getUniformLocation(p, 'u_mouse'), mouseX, mouseY);
+  gl.uniform2f(gl.getUniformLocation(p, 'u_tile_res'), tileWidth, tileHeight);
+  gl.uniform1i(gl.getUniformLocation(p, 'u_scene'), 0);
+  gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);
+}
+function frame(now) {
+  if (previous !== undefined) time += (now - previous) * 0.001 * speed;
+  previous = now;
+  gl.bindFramebuffer(gl.FRAMEBUFFER, framebuffer);
+  gl.viewport(0, 0, tileWidth * 4, tileHeight * 2);
+  draw(scene, tileWidth, tileHeight);
+  gl.bindFramebuffer(gl.FRAMEBUFFER, null);
+  gl.viewport(0, 0, canvas.width, canvas.height);
+  gl.activeTexture(gl.TEXTURE0); gl.bindTexture(gl.TEXTURE_2D, texture);
+  draw(ice, canvas.width, canvas.height);
+  if (shot) {
+    // Headless Firefox does not composite WebGL; expose the actual rendered pixels.
+    const pixels = new Uint8Array(canvas.width * canvas.height * 4);
+    gl.readPixels(0, 0, canvas.width, canvas.height, gl.RGBA, gl.UNSIGNED_BYTE, pixels);
+    const output = document.createElement('canvas');
+    output.width = canvas.width; output.height = canvas.height;
+    const ctx = output.getContext('2d'), image = ctx.createImageData(output.width, output.height);
+    for (let y = 0; y < output.height; y++)
+      image.data.set(pixels.subarray((output.height - y - 1) * output.width * 4, (output.height - y) * output.width * 4), y * output.width * 4);
+    ctx.putImageData(image, 0, 0); canvas.replaceWith(output);
+  } else requestAnimationFrame(frame);
+}
+if (shot) frame(0); else requestAnimationFrame(frame);
+</script>
+</body>
+</html>