Aurora Borealis Demo Creation

The task says "Wake up and do as you please." Based on my purpose, I should create cool Three.js demos in my space under /space/demos/. The last execution created demo 014-neon-rain. So I should create a new demo, presumably 015-something.

Let me start by installing shell tools and exploring the current state of the demos folder.

Let me look at the current state of the demos folder to see what demos exist and what the index page looks like.

Let me see the full index to understand the demo list format, and check what demos exist so I can pick a fresh idea. Demos so far:

1. 001-spinning-cube
2. 002-nebula-galaxy
3. 003-mandelbulb-explorer
4. 004-fluid-dynamics
5. 005-gravity-sandbox
6. 006-event-horizon
7. 007-sonic-reactor
8. 008-void-runner
9. 009-azure-odyssey
10. 010-abyssal-bloom
11. 011-physarum-garden
12. 012-powder-alchemy
13. 013-clockwork-nebula
14. 014-neon-rain

Let me look at the full index to see the descriptions and get a sense of what's been done.

I have 14 demos. Time to create demo 015. Let me brainstorm something fresh that hasn't been done:

Done so far:

1. Spinning cube (basic)
2. Nebula galaxy (particles)
3. Mandelbulb explorer (ray marching fractal)
4. Fluid dynamics (GPU Navier-Stokes)
5. Gravity sandbox (N-body)
6. Event horizon (black hole lensing)
7. Sonic reactor (audio visualizer)
8. Void runner (endless runner game)
9. Azure odyssey (sailing / ocean)
10. Abyssal bloom (deep sea boids)
11. Physarum garden (slime mold GPU)
12. Powder alchemy (falling sand)
13. Clockwork nebula (steampunk orrery gears)
14. Neon rain (cyberpunk city rain)

Ideas for 015:

• Terrain erosion simulator — procedural terrain with hydraulic/thermal erosion, fly over it
• Aurora borealis — volumetric aurora curtains with GLSL, snowy terrain, stars
• Cloth simulation — flags, cloth tearing
• Ray-traced scene — real-time path tracing (spheres, cornell box) with progressive accumulation
• Voxel world — Minecraft-like with caves
• Fireworks show — procedural fireworks with audio
• Solar system — done-ish via clockwork nebula
• Lightning storm / plasma globe
• Fractal forest / L-systems
• Water caustics pool
• Kaleidoscope / mandala
• Space elevator / dyson swarm
• Portal / non-euclidean
• Reaction-diffusion (Gray-Scott) — Turing patterns, not done yet! Could be beautiful: GPU reaction-diffusion on a 3D surface or plane, with feeding interactions.
• Wormhole / tunnel
• Flocking murmuration of starlings — boids done in abyssal bloom though
• Origami / paper folding
• Magnetic field lines / ferrofluid
• Crystal growth / snowflake simulation
• Volcanic eruption with lava flows
• Tornado / hurricane simulator with debris
• Interactive spider web with physics
• Underwater done; space done; city done; ocean done

A strong candidate: Real-time path tracer — progressive path tracing in GLSL with spheres, boxes, cornell box, depth of field, importance sampling. That's technically impressive and visually gorgeous. But can be heavy; still, a small scene at low res with temporal accumulation works well.

Another strong candidate: Aurora Borealis — volumetric ray-marched aurora curtains over a snowy procedural landscape with a frozen lake reflecting, stars, moon, shooting stars, maybe a cabin with warm light. Very different palette from previous demos (no aurora yet). Could add synthesized ambient wind audio. This is very doable and visually stunning.

Another: Reaction-diffusion — Gray-Scott on GPU with pointer feeding, mapped onto a 3D blob/plane, with color palettes. Physarum was similar-ish (agent-based pattern formation). Maybe too close.

Another: Terrain erosion — procedural heightmap terrain with hydraulic erosion simulation running live on GPU, camera fly-through, rivers form, sediment. Very cool and educational. Combined with water rendering.

Another: Fireworks — procedural fireworks over a night city/water with reflections, launch with clicks, choreographed show mode, synthesized boom audio. Fun, interactive, impressive with bloom. Could be combined with a harbor scene.

Another: "Starling murmuration" — 50k GPU boids forming a murmuration over a sunset field. Boids were done in abyssal bloom (2.3k fish). A murmuration with 50k+ birds via GPGPU would be a scale-up but conceptually similar.

Another: Kinetic sand / zen garden?

Another: "Chrono Bloom"?

Another: Portal cube / hypercube (4D tesseract projection) — 4D polytopes projected to 3D, interactive rotation in 4D planes. Educational and trippy. Could do multiple 4-polytopes (tesseract, 16-cell, 24-cell, 120-cell), stereographic projection, cell highlighting. That's a nice math-y demo we haven't done.

Another: Weather machine / tornado — a volumetric tornado with debris particles, destructible barn? Fun physics.

Another: "Ink in water" — 3D fluid? 2D fluid done.

Another: Ferrofluid / metaballs — ray-marched metaballs with surface tension, magnetic blobs.

Another: Aurora + path tracing? Keep scope manageable.

Let me think about what would be most impressive and distinct:

1. Aurora Borealis ("Polar Lights"): ray-marched volumetric curtains, procedural snowy mountains, frozen lake with reflection, stars/milky way, moon, shooting stars, cabin with smoke, ambient wind audio, presets. Distinct from neon-rain (city) and azure-odyssey (ocean day). Night arctic scene. Very beautiful. Medium-high complexity but achievable.

2. Progressive path tracer ("Glass & Light"): Cornell-box-like scene with spheres, refractive glass, glossy metals, depth of field, progressive accumulation, camera orbit resets accumulation. Very "wow" for graphics nerds. Complexity moderate; risk: performance on weak GPUs; but can render at reduced res with accumulation.

3. Hydraulic erosion terrain: unique, educational. Complexity high (GPU erosion sim + nice rendering). Risk of bugs.

4. 4D polytope explorer: unique math demo, less "visual wow" but trippy with stereographic projection + bloom.

I think the aurora demo hits the sweet spot: distinct setting, gorgeous visuals, achievable in one file, lots of features (ray-marched volumetric aurora with animated curtains, terrain, ice reflection, stars, meteors, audio, camera modes, presets, snapshots). Let me go with "015-polar-lights" or "015-aurora". Name: "Aurora Borealis" — folder 015-aurora-borealis.

Plan the demo:

Scene composition:

• Fullscreen approach: I'll do a hybrid:

  • Terrain: procedural heightmap mesh (fbm ridges, snow shading, frozen lake plane at low elevation).
  • Sky: big sphere with procedural stars + milky way + moon.
  • Aurora: ray-marched in a fullscreen-ish pass? Or on a cylinder shell? Better: render aurora in the sky shader itself — ray-march a volumetric curtain field when looking up. Common technique: aurora as layered "curtain" sheets defined by fbm along rays; integrate along view ray through a slab above horizon. Can be done in the sky fragment shader with ~20-40 steps, only above horizon.
  • Alternatively render aurora as several large transparent curtain meshes with animated shader — cheaper and controllable. But ray-marched volumetric looks way better.

  Approach: sky dome shader includes: stars (hash), milky way band (fbm), moon disc with glow, and aurora ray-marching: for view directions with y > 0, march along ray between altitudes ~ [0.15, 0.6] (normalized), sample curtain density = fbm(xscale - t, zscale) shaped into vertical curtains with height falloff; accumulate emission with color gradient (green #00ff88 at bottom → purple/blue top). Add subtle red fringe. Use ~24 steps with jitter. Should look great with bloom.

• Frozen lake: circular flat area in terrain center with reflective ice — use a simple planar reflection? We already did a reflector in neon-rain. Could reuse a lightweight planar reflection for the lake: render scene mirrored into RT at half res, sample with distortion. That doubles draw but scene is cheap (terrain + sky). Actually the sky shader with ray-marched aurora is the expensive part; rendering it twice is heavy. Alternative: fake reflection — the ice shader computes reflection direction and samples the SAME sky function analytically (aurora is a function of direction!). Since aurora/stars are computed in a shader as f(dir), the ice can call the same GLSL function with reflected dir at reduced quality (fewer steps). That's elegant: shared GLSL chunk skyColor(dir, quality).

• Terrain: radial island with mountains around, snow with sparkle glints, some rocks. Heightmap via fbm in JS, displace plane geometry; normals computed. Snow shader: white with blue-ish ambient, sparkle via hash glints, slope-based rock exposure. Add a few low-poly pine trees? Instanced cones — nice touch: instanced spruce trees (2 cones + trunk) scattered on slopes, snow-covered. Adds life. Maybe a small cabin with warm window light + chimney smoke particles? Smoke adds complexity; maybe skip cabin, keep wilderness. Actually a tiny cabin with glowing windows gives scale and warmth — include it, simple box + roof + emissive windows, plus light halo sprite. Smoke: small particle system, cheap. Let's include.

• Meteors/shooting stars: occasional streaks across sky — particle/lines with fading trail, spawned randomly.

• Snowfall: gentle falling snow particles around camera (GPU points with wrap-around box), adds immersion.

• Ground fog / mist near lake: soft billboards or just fog. Use scene fog + a few drifting mist sprites.

• Moon with glow; stars twinkle.

Audio (WebAudio synthesized):

• Wind: filtered noise with slow LFO on filter freq + gusts.
• Sparse crystalline "aurora shimmer": gentle high sine chimes triggered randomly with reverb (convolver might be heavy; use feedback delay).
• Optional crackle of ice? Keep wind + chimes + low drone pad.
• Mute toggle, volume.

Interaction & cameras:

• OrbitControls default around lake.
• Camera modes: Orbit / Drone fly (auto slow fly over terrain) / Ice-level walk (low over lake, look at sky) — or "Lie on ice" mode looking up.
• Click sky: launch a meteor manually? Or click to spawn meteor at pointer. Nice: "click anywhere to call a shooting star".
• Keys: 1/2/3 cameras, P photo, M mute, etc.

Post-processing: UnrealBloomPass (aurora loves bloom), maybe subtle vignette+grain via shader pass. OutputColorSpace handling.

UI:

• Title panel, collapsible controls: aurora intensity, curtain count/speed, color theme (classic green-purple / crimson / electric blue / rainbow), star density, snowfall amount, wind volume, bloom strength, quality toggle (aurora march steps), presets (Quiet Night, Solar Storm, Crimson Dawn, Frozen Blue), snapshot button, FPS meter maybe.

Performance: aurora ray-march is the hot spot. Render at devicePixelRatio capped 1.5; quality setting adjusts steps (16/24/36). The sky is a big inverted sphere; fragments only march when dir.y > horizon-ish. Terrain occludes lower hemisphere anyway.

Implementation details:

Shared GLSL: I'll write the sky as a ShaderMaterial on a backside sphere radius ~ 900 (within far plane). Include noise: hash, value noise 2D/3D, fbm. Aurora function:

Curtain shape: density along x with several "bands" — use fbm(p.xz * s1 + wind*t) to warp, then curtain = smoothstep on ridged noise of warped x. Add fine vertical striations via high-freq noise on x only. Multiply by large-scale mask so aurora appears in arcs across the sky, not everywhere.

Also animate: curtains drift, ripple with time; intensity flickers slowly.

Stars: hash-based points with twinkle; milky way: fbm band along a tilted great circle; moon: disc in fixed dir with limb darkening + halo.

Ice reflection: lake is a disc mesh (radius r) at y=0. Its shader: compute reflected dir R = reflect(-V, up) with slight normal perturbation (ice ripples/cracks via noise), then color = skyColor(R, lowQuality) * fresnel + deep ice base color + cracks (voronoi-ish lines) + subtle parallax bubbles? Keep: fresnel mix of dark blue ice with reflected sky, plus sparkle. Since skyColor includes aurora, reflection shows the lights — gorgeous.

To share GLSL between materials, define a string SKY_GLSL with functions and prepend to both shaders, with uniforms: uTime, uAuroraIntensity, uCurtainScale, uSpeed, uColorTheme, uStarDensity, uMoonDir, uSteps (as #define via string replace or uniform int — loop with constant max and break on uniform). I'll use a #define injected at compile: AURORA_STEPS ${steps} and recompile on quality change (material.needsUpdate). Simpler: fixed MAX_STEPS loop with early break by uniform float uQuality (0..1) controlling step size... Early break in WebGL2 GLSL ES 3.0 is fine with dynamic conditions. Three r160+ uses WebGL2 by default → GLSL ES 3.00 via auto-conversion. I'll write GLSL1-style (texture2D etc. auto-converted) but dynamic break is allowed in ES 3.0. Safe approach: for (int i=0;i<48;i++){ if(i>=uSteps) break; ...} — allowed.

Terrain shader: custom ShaderMaterial with height-based snow/rock, sparkle glints (hash on world pos + view dot), moon dir lighting + aurora ambient tint (fake: tint snow slightly green by sampling aurora average intensity uniform), fog.

Trees: instanced — trunk cylinder + 2-3 cone layers; use MeshStandardMaterial? Mixing standard materials with custom sky is fine. But lighting: scene has directional "moon" light + ambient. Standard materials with bloom pass OK. To keep style coherent, use MeshStandardMaterial for trees/cabin with a dim blue directional light (moon) + hemisphere. Snow terrain custom shader is fine.

Actually simpler & coherent: use MeshLambertMaterial/Standard for trees & cabin; terrain custom; lake custom; sky custom. Bloom pass picks up emissive (cabin windows, moon, aurora bright parts, meteors).

Snowfall: Points ~3000 in a box around camera, shader animates fall + sway with time, wrap via mod. Size attenuation, soft round sprite via fragment discard/alpha.

Meteors: pool of ~8; each meteor = head (additive sprite) + trail (fading line strip or stretched plane billboard). Simple: use a Points system with per-particle age, or individual meshes. I'll do: each meteor has a head Sprite (additive) and a TrailRenderer-ish line of last N positions using THREE.Line with vertexColors alpha fade. Cheap. Spawn randomly every 4-9s and on click (ray to sky dome direction).

Cabin smoke: small Points system, ~60 particles looping upward with growth+fade.

Mist: ~10 large soft sprites drifting slowly near lake surface, additive-ish low alpha.

UI: right-side panel (collapsible), consistent with previous demos' style (dark glass). Buttons: presets row, sliders: Aurora intensity, Activity (speed), Curtain density, Star density, Snowfall, Wind audio volume, Bloom, Exposure? Keep manageable: intensity, speed, scale, theme select, stars, snow, bloom, quality select, volume. Camera mode buttons + snapshot + mute. Keyboard shortcuts listed.

Presets:

• "Quiet Night": low intensity 0.5, slow, few curtains, green.
• "Solar Storm": intensity 1.3, fast, dense, green-purple, more meteors.
• "Crimson Rare": red/pink theme.
• "Ice Blue": blue theme. Also randomize seed button?

Theme colors: pass 3 colors (bottom, mid, top) as uniforms; themes define them.

FPS: small stats readout (custom, frames per second avg).

Snapshot: render then toDataURL download png.

Let me also double check three.js CDN usage from previous demo to stay consistent (import map with unpkg three@0.160+ or jsdelivr). Let me peek at 014's header for the import map and general structure to reuse conventions (and maybe the Reflector code isn't needed). Let me look at a bit of 014 for style reference (UI panel css etc.). It's 1619 lines; I'll skim the top.

Then write the new demo file. This will be a big file (~1300-1600 lines). I need to be careful with GLSL correctness and JS syntax. After writing, run node --check on extracted JS? The JS is inside HTML as module; I can extract script contents and syntax-check with node (as .mjs). Also verify IDs referenced exist.

Let me start. First peek at 014 quickly for import map + UI conventions.

**************************************************************************************************ly.

I have the conventions. Now I'll create demo 015: Aurora Borealis — Polar Lights. Folder: /space/demos/015-aurora-borealis/.

Let me design the full demo carefully, then write it in one go.

Architecture

File: /space/demos/015-aurora-borealis/index.html

Scene graph:

• skyMesh: SphereGeometry(1500, 48, 24), BackSide ShaderMaterial — contains stars, milky way, moon, aurora ray-march. fog: false, depthWrite false, renderOrder early.
• terrain: big radial terrain, PlaneGeometry(2400, 2400, 220, 220) displaced by fbm height function in JS; custom ShaderMaterial (snow/rock/sparkle, moon light, aurora ambient tint, fog).
• lake: CircleGeometry(190, 64) at y = 0.4 (slightly above terrain min in the basin — terrain function should carve a flat basin near center below y=0.4). Custom ShaderMaterial: ice with reflection of sky (calls shared sky GLSL), cracks, sparkle, fresnel.
• trees: InstancedMesh of a merged spruce geometry (trunk + 3 cones) ~600 instances on slopes within radius 200-900, avoiding lake. MeshStandardMaterial? For stylistic coherence and cheap lighting, I'll use MeshLambertMaterial with vertexColors? InstancedMesh with single color + per-instance color via instanceColor for variation. Lighting: dim blue directional (moon) + hemisphere (sky blue / ground dark). Snow on trees: use Lambert with two materials? Merged geometry with groups is complicated. Alternative: custom cheap shader for trees too? Keep simple: MeshStandardMaterial flatShading white-ish blue tint, plus separate snow caps? Simpler: color the cones dark blue-green with slight emissive nothing; moon light gives shading. Add snow by making upper cone color lighter via vertex colors baked in merged geometry (color per part) and material.vertexColors = true. That works with Lambert/Standard.
• cabin: small group: box walls (warm brown), roof prism (snow white), window planes with emissive material (bloom picks up), chimney + smoke particles, warm PointLight (low intensity, small radius) — maybe fake with emissive + sprite halo instead of real light to save perf. Use one PointLight (intensity 30, distance 60, decay 2) — cheap enough.
• snowfall: Points ~2500, shader-based falling within a 260-box around a center that follows camera (wrap by mod in shader with uniform uCamPos).
• meteors: pool of 10; each: head = Sprite additive, trail = THREE.Line with 24 points updated per frame, fading colors. Spawn logic.
• mist: 12 Sprites with radial gradient texture, slow drift over lake.
• Moon: part of sky shader (disc + halo).

Post: EffectComposer + RenderPass + UnrealBloomPass (strength ~0.9, radius 0.6, threshold 0.55) + custom final ShaderPass (vignette + grain + slight chromatic? keep vignette+grain+exposure). OutputPass at end for color space. With three 0.160, use OutputPass; my custom grade pass can include tone mapping? Simpler: composer with RenderPass → BloomPass → OutputPass, and put vignette/grain into a final custom pass after OutputPass operating in sRGB — fine.

Actually order: RenderPass → UnrealBloomPass → OutputPass (tone map + sRGB) → GradePass (vignette/grain). Set renderer.toneMapping = ACESFilmic, toneMappingExposure adjustable. OutputPass respects renderer settings.

Shared sky GLSL: a template string with:

• uniforms needed: uTime, uAurora (intensity), uSpeed, uDensity (curtain density), uSteps, uColA (bottom green), uColB (mid), uColC (top), uStarAmt, uMoonDir, uSeed.
• functions: hash11/21/31, noise2/3, fbm2/3, stars(dir), milkyWay(dir), moon(dir), aurora(ro, rd) → vec3, skyColor(ro, rd, withAurora) → vec3.

Sky dome fragment: gl_FragColor = vec4(skyColor(cameraPos, normalize(vWorldPos - cameraPos), true), 1.0) — wait, camera pos relative to world; sky sphere centered at origin, radius 1500; camera stays within ~±1000. ro = cameraPosition (world), rd = normalize(vWorld - cameraPosition).

Lake fragment: R = reflect(viewDir, n) where n = perturbed up; col = mix(iceBase, skyColor(vec3(0, 2, 0)+worldPos, R, true*lowSteps), fresnel...) — reflection ray origin: worldPos on lake (y≈0.4). Aurora altitude slab in "world" units: h0=180, h1=520. Ray-march in world space — consistent between sky & lake.

For the lake reflection, use fewer steps (uStepsRefl = max(8, uSteps/2)).

Aurora model (the heart — must look good):

Hmm — classic approach (from shadertoy "Auroras" by nimitz): tri-noise based volumetric. I'll write my own:

• Large mask: mask = smoothstep(0.35, 0.75, fbm(q*0.5 + t*0.008)) → arcs regions.
• Curtain: c = pow(1 - abs(2*fbm(q*vec2(1.2,0.35) + warp) - 1), 3) elongated along one axis → curtains hanging like ribbons. Elongate along z by scaling z less? Curtains typically arc across the sky; elongation direction varies. Fine.
• Striations: multiply by 0.6 + 0.4*noise(vec2(q.x*40, t)) high-frequency vertical rays.
• Height profile: hp = smoothstep(H0, H0+40, h) * smoothstep(H1, H0+120, h) with extra brightness near bottom edge: edge = exp(-(h-H0)*0.02).
• Color: mix(uColA, uColB, smoothstep(H0, H10.7, h)) then add uColC at top faintly. Multiply intensity, accumulate front-to-back with alpha ~ densitystep.

Add subtle time flicker: flick = 0.85 + 0.3*noise(t*0.5) global.

Also rays "rays" structure: multiply by vertical streak function of x only: rays = 0.5 + 0.5 * sin(q.x*90 + fbm(q*3)*20 + t*2)? Might be too regular; use noise instead.

I'll iterate mentally to keep it plausible; with bloom it'll look soft and gorgeous.

Terrain height function (JS, mirrored in shader? no — shader gets displaced positions + normals from geometry; snow shading uses world pos & normal only, plus sparkle hash). JS fbm:

Lake radius 190 at y=0.35; terrain at r<190 should be < 0.35 (e.g., -4..-8) so water/ice covers. Between 190 and ~260 shoreline rises above 0.35. mask smoothstep(150, 320, r) * base ensures shore rise. Let me define:

ridged fbm: n = 1 - abs(noise), squared, 4 octaves, range ~0..1 → *300 gives peaks up to ~300+40 near r>420. Good: mountains ring the lake.

Normals: computeVertexNormals after displacement.

Terrain shader:

• varying vWorldPos, vNormal.
• snow color base: #dfe9f5 slightly blue; slope = 1 - normal.y → rock color #2a2f3a mix.
• lighting: moon dir uniform, diffuse = max(dot(n, moonDir),0) * moonColor(0.55,0.65,0.85)*1.1; ambient = vec3(0.10,0.13,0.20) + auroraTint * uAuroraGlow (uniform updated = average aurora intensity * theme color, subtle green bounce).
• sparkle: g = step(0.997, hash(floor(wp.xz*7.0) + floor(wp.y*7.0))) times view-dependent glint: pow(max(dot(reflect(-V,n), moonDir),0), 8) → twinkling; multiply by sparkle mask noise so patches.
• distance fog: exp2 fog toward horizon color (dark blue #0a1020), fog near 200 far 1600. Also height fog near lake? skip.
• aurora sky reflection on snow: add uAuroraGlow * themeColor * 0.06 * snowMask.

Trees: generate spruce geometry: trunk (CylinderGeometry(0.35,0.5,3,5)) brown #3a2c22; 3 cones (ConeGeometry) radii 2.6/2.0/1.3, heights 4.5/3.6/2.8, positioned y 2.5/5/7.2, color dark spruce #16281f with snow tint on top cone? Bake vertex colors: for cone vertices, mix color toward white by (localY within cone) → snowy tips. Merge via BufferGeometryUtils.mergeGeometries with groups? Use mergeGeometries([...]) after applying vertex colors to each; material: MeshStandardMaterial({vertexColors:true, roughness:0.9, flatShading:true}). Instanced ~700: position r in [210, 950], slope check via height function gradient, scale random 0.7-1.6, rotation random. Also small chance of dead tree (just trunk)? skip.

Need BufferGeometryUtils import from addons.

Cabin: at fixed spot (x=120, z=-80?) on shore r≈145? Lake radius 190 — cabin should be beyond shoreline: r≈230. Position (170, h, -150) → r = sqrt(170²+150²)=226. OK. Flatten terrain there: add flattening term in height function around cabin pos: h = mix(h, cabinY, smoothstep(28, 10, dist)). Cabin: base box 10x5x8, roof: two sloped boxes or a prism via ExtrudeGeometry — simpler: use a rotated box pair? Use CylinderGeometry with 3 radial segments as prism! CylinderGeometry(r, r, len, 3) rotated gives triangular prism — nice roof. Snow cap: slightly larger thin prism on top white. Windows: two planes emissive #ffb45c * 2.2 (bloom). Door dark. Chimney small box; smoke: Points 50 particles cycling up 12m, drifting with wind, alpha fade, size grow. Halo sprite additive warm at window. PointLight warm (0xffa050, 18, 55, 2) at window height.

Snowfall: Points 2600; attributes: seed(4): rand xyz in box + rand speed. Shader: pos = mod(seedPos - vec3(0, tfallSpeed, 0) + wind drift, box) - box/2 + uCenter (camera pos snapped). Size 2-5px * attenuation; fragment: soft circle alpha 0.8. uSnow uniform scales count via draw range or alpha cutoff: use if(seed.w > uSnow) discard in vertex by gl_PointSize=0? Simplest: geometry.setDrawRange(0, countuSnow).

Meteors: pool 10. Each active meteor: start pos on sky dome r=1400 random azimuth/elevation>25°, direction tangent-ish downward, speed 700-1000 m/s, life ~1.2s. Head: additive Sprite scale 26, color white-blue. Trail: Line with 26 vertices; each frame unshift head pos, recompute colors alpha fade; geometry.attributes update. Spawn: random every 3-8s (more during Solar Storm), click spawns at pointer ray (point on dome along ray). Also bright flash? subtle. Sound: soft whoosh (filtered noise sweep) — nice touch.

Mist: 12 sprites, radial gradient canvas texture, scale 60-140, y≈2-6 above lake, slow drift + alpha 0.05-0.12, additive? normal blending, color #9db8dd.

Audio:

• master gain, mute toggle.
• wind: two noise buffers (looped 4s white noise buffer) → lowpass 300-900Hz with LFO, gain gusts via slow random LFO (use setTargetAtTime automation loop via JS interval or LFO on gain via oscillator). Simple: noise → biquad lowpass(freq modulated by LFO osc 0.07Hz depth 250) → gain 0.5 → master. Second layer: bandpass 1200 noise quiet for whistle, LFO 0.11Hz.
• drone pad: two detuned sine/triangle oscillators (55Hz, 82.5Hz, 110Hz?) through lowpass, very quiet (0.05), slow amplitude LFO — polar stillness.
• chimes: random pentatonic high sines (e.g., A5, C#6, E6, F#6, B6) with exponential decay 3-6s, triggered every 6-14s randomly, quiet 0.06, through feedback delay (0.45s, fb 0.35) for space. Tie to aurora flicker? Just random.
• meteor whoosh: bandpass noise sweep 400→2000Hz, 0.8s, gain envelope.
• camera walk mode: soft snow crunch? skip.

Audio starts on first user gesture (button click). btn-audio toggles.

Cameras:

1. Orbit: OrbitControls target (0, 30, 0), camera start (0, 90, 420). enableDamping. minDistance 40 maxDistance 900, maxPolarAngle 1.52 (don't go under terrain much).
2. Drone fly: auto path — camera follows slow spline circle r≈500, height 120-200 sine, lookAt lake center + slight ahead; user drag temporarily offsets? Keep simple: auto only, any drag returns to orbit mode.
3. Ice level: camera at y≈3 gliding slowly over lake circle r≈60, looking up at 35° toward the brightest aurora heading, slow pan — "lie on the ice" vibe. Slight head-bob none.

Transitions: lerp camera position/quaternion over 1.5s (store from/to, ease). Implement simple tween.

UI:

• title panel: "AURORA BOREALIS", sub "69.6°N · Polar Night · Kp 5", hint lines.
• controls panel: rows:
  • camera modes: Orbit / Drone / Ice buttons
  • buttons: Pause, Bloom, Sound, Photo
  • sliders: Intensity (0-1.5), Activity(speed), Curtains(density), Stars, Snow, Bloom strength, Volume
  • theme select: Emerald, Crimson, Electric, Rainbow
  • preset buttons: Quiet Night / Solar Storm / Crimson Sky / Deep Blue (maybe theme presets combine)
  • quality select: Low/Med/High (aurora steps 14/22/34)
• stats panel: fps, draw calls?, camera mode.
• loading overlay: "AURORA BOREALIS" + tip.

Keyboard: 1/2/3 cameras, Space pause, B bloom, M sound, P photo, H hide UI, F meteor? (or click). R randomize seed.

Snapshot: composer.render(); canvas.toBlob → download 'aurora.png'. Need preserveDrawingBuffer or render immediately before toBlob in same frame — do composer.render() then toDataURL synchronously; works without preserveDrawingBuffer if same task.

Randomize seed: uSeed uniform offsets noise inputs; re-randomize meteor timer.

Performance guards: cap DPR at 1.5; quality presets change steps & bloom resolution? Keep bloom fixed half res (UnrealBloomPass internally downsamples).

Code structure (module script):

1. imports
2. config/state object S with all params
3. renderer/scene/camera/composer setup
4. shared GLSL string SKY_COMMON (functions) — used by skyMat & lakeMat (and maybe terrain for aurora tint? terrain just uses uniforms)
5. build sky, terrain, lake, trees, cabin+smoke, snowfall, mist, meteors, moon? (moon in sky shader)
6. audio module object
7. UI wiring
8. camera modes + transitions
9. resize
10. animate loop: dt clamp, update uniforms, snowfall center follows camera, meteors update, smoke update, mist drift, controls update, composer.render, fps counter
11. snapshot, keyboard

Careful GLSL notes (three r160, WebGL2, but ShaderMaterial default GLSL1 syntax auto-upgraded): use texture2D, varying, gl_FragColor — three auto-converts. Dynamic break in for loop OK in ES3.

One risk: in the shared GLSL, function skyColor uses uniforms — fine since same uniforms declared in both materials.

Noise: implement value noise 2D & 3D with hash based on sin — classic:

Aurora marching (sky): ro = cameraPosition (world), but for sky dome the effective origin doesn't matter much; use ro.y small (~0-500). Slab H0=170, H1=560.

Tune constants later-ish; pick sane values. Also multiply final by (0.8 + 0.4*flickerNoise).

Stars:

Only where rd.y > -0.05. Multiply by (1 - aurora-ish?) no, fine.

Milky way: band around a great circle with normal n = normalize(vec3(0.5, 0.25, 0.8)): dist = abs(dot(rd, n)); band = smoothstep(0.5, 0.0, dist); density = fbm3(rd3.5 + seed) → col = band(density^2)*vec3(0.5,0.6,0.9)*0.35 + dark lanes (subtract fbm). Subtle.

Moon: uMoonDir = normalize(vec3(-0.45, 0.38, -0.6)) something above horizon. disc: d = dot(rd, moonDir); disc = smoothstep(cos(0.028), cos(0.024), d); surface shading: crater noise via fbm on projected coords * limb darkening; halo = pow(max(d,0), 600)*... plus wide glow pow(d, 24)*0.12. Moon color warm white (1.0, 0.96, 0.88)*2.2 for bloom.

Also horizon glow: faint light pollution? Add subtle gradient near horizon: vec3(0.05,0.08,0.13)*(1-rd.y) for y in 0..0.25 — blends with fog color of terrain. Terrain fog color should match sky horizon: #0b1220-ish. I'll set sky base gradient: mix(horizon #101a2c, zenith #02040a, pow(rd.y,0.6)) plus faint horizon band of dark teal.

Terrain fog color: same horizon color #0d1626.

Lake ice shader:

• varying world pos; normal mostly up; perturb: n = normalize(vec3(nx, 1, nz)) with nx/nz from fbm gradient small (0.03) animated very slowly (ice barely moves; maybe static cracks + slight shimmer).
• R = reflect(-V, n); R.y = abs(R.y).
• skyRef = skyColor(vec3(wp.x, 1.5, wp.z), R) with uStepsRefl (use uniform int uStepsR).
• fresnel = pow(1 - max(dot(V, n),0), 3) *0.85 + 0.15.
• iceBase: deep #061018 with bubbles: fbm layers; cracks: voronoi edge — cheap crack: c = abs(fbm2(wp.xz*0.35)) lines where c<0.02 → white-ish. Or use ridged: crack = smoothstep(0.02, 0.0, abs(noise-0.5))... I'll do two-scale crack lines: v = noise2(wp.xz*0.22); crack = smoothstep(0.025, 0.0, abs(v-0.5)) * 0.5 + second scale.
• snow patches on ice: mask = smoothstep(0.55,0.75, fbm(wp.xz*0.02)) → mix toward snow color (matte, lit by moon).
• final = mix(iceBase + cracks, skyRef, fresnel) + sparkle glints + snowPatches.
• Also near-shore blend to terrain? The terrain is under the lake (below y 0.35) so edge intersection is hidden by shoreline rising. OK.

Terrain snow sparkle: glint = pow(max(dot(reflect(-V, n), moonDir),0.), 24.) * step(0.995, hash(floor(wp9))) — but floor(wp9) with wp large → hash precision issues at 2000 units? sin-hash breaks beyond ~1e4. wp9 up to 18000 → borderline. Use fract-based hash without sin: the "hash without sine" ( fract(p0.1031) style ) is more stable. I'll use those. Still fine.

Trees placement: sample random r∈[215, 980], θ; compute h via JS height func; accept if h > 1.5 (above shore) and slope < 0.55 (estimate gradient by finite difference); scale by (0.8 + rand*0.9) * (1 - smoothstep(600, 950, r)*0.5); also cluster: accept with prob based on fbm "forest mask" noise → clumps. 700 instances max; try 2000 samples.

Also add a few trees near cabin.

Cabin smoke: Points 60; each particle: birth offset i/60 * life(6s); pos = chimney + upt2.2 + wind drift (x += t1.1 + sin) ; size 3→14; alpha 0.35(1-t/6)*smoothstep start. Shader-driven with uTime — stateless.

Mist sprites: drift x += sin(t0.05+i)... store base pos; alpha pulse.

Meteor trail: use Line with BufferGeometry 26 points; update positions each frame: shift array. Material LineBasicMaterial vertexColors, transparent, blending additive, depthWrite false. Lines are 1px — thin but with bloom will glow. Head sprite scale ~20 additive. Good enough. Alternatively use a stretched plane for trail — skip, line+bloom fine.

Click → meteor: raycast from camera through NDC to sphere r=1400 → spawn meteor starting there with random tangent dir. Also small chance click near horizon does nothing (y<0.05 → clamp).

Aurora average for terrain tint: compute on CPU approx: uAuroraGlow = S.intensity * (0.35 + 0.3sin(t0.1)) clamp; color = theme bottom color. Update uniform per frame.

Themes:

• Emerald: A #2bff8a (green), B #28c8ff? classic: bottom green #39ff8e, mid teal #19d3c5, top purple #8a4bff.
• Crimson: bottom #ff5a3c, mid #ff2d78, top #7a2bff.
• Electric: bottom #37e6ff, mid #3f7bff, top #b04bff.
• Rainbow: bottom #ffe14d? rainbow: bottom #52ff7a, mid #4dc9ff, top #ff4dd2. Fine.

Presets:

• Quiet Night: intensity .55, speed .5, density .7, stars .8, snow .35, theme Emerald, steps med.
• Solar Storm: intensity 1.25, speed 1.6, density 1.4, stars .5, snow .15, Emerald, meteors frequent, steps high.
• Crimson Sky: intensity .95, speed .9, density 1.0, theme Crimson.
• Deep Freeze: intensity .7, Electric theme, snow 1.0, stars 1.0.

Quality: Low: steps 14, refl 8, DPR 1; Med: 22/12, DPR 1.25; High: 34/18, DPR min(1.6, devicePixelRatio). Changing quality sets uniforms + renderer.setPixelRatio + composer.setSize.

FPS counter: frames over 500ms → update stats.

Now — write the code. It's long; I'll write carefully section by section. I'll write the file with a heredoc via cat > file << 'EOF' to avoid JSON escaping issues? The write tool read_write_file_in_shell_environment with mode write takes content directly — large content is fine but JSON escaping of quotes/newlines is handled by the tool invocation format. Writing ~60KB in one tool call is OK (previous demo was 65KB written presumably in one call). I'll use the write tool. Risk: extremely long single message; acceptable.

Actually, to reduce risk of a truncated write, I'll write in 3-4 parts: part 1 (HTML head + CSS + body UI), then append JS in chunks via execute_shell_command with heredoc? Appending via cat >> with quoted heredoc 'EOF' is safe for $ and backticks. But the content includes EOF? No. Heredoc in the command string — the command itself is passed as JSON string; newlines fine. But mixing: I'll use read_write_file for part 1, then execute_shell_command heredocs for appends. Hmm, heredoc content with backticks and ${} is safe inside quoted 'EOF'. GLSL has backticks? No. JS template literals have ${} — safe in quoted heredoc. OK.

Plan:

1. mkdir -p /space/demos/015-aurora-borealis
2. Write part 1 (head/css/body/open script) via write tool.
3. Append part 2 (JS: setup + GLSL lib) via heredoc.
4. Append part 3 (scene builders).
5. Append part 4 (audio + UI + loop + closing tags).
6. Extract JS, node --check.
7. Grep ID cross-refs.
8. Update index.html (add card after the comment).
9. Done.

Let me now write the actual code mentally with care for correctness.

Key three.js r160 APIs:

• new THREE.WebGLRenderer({canvas, antialias:true}) — but with composer, MSAA doesn't apply to render targets; fine (bloom smooths). Could use samples on composer's target: EffectComposer creates HalfFloatType RT in r160? Default UnsignedByteType unless... In r152+, EffectComposer defaults to HalfFloatType. Good for HDR bloom. Set renderer.toneMapping = ACESFilmicToneMapping; OutputPass applies it.
• OrbitControls from 'three/addons/controls/OrbitControls.js'
• EffectComposer, RenderPass, UnrealBloomPass, OutputPass, ShaderPass from addons.
• BufferGeometryUtils from 'three/addons/utils/BufferGeometryUtils.js' → mergeGeometries.

Custom final grade pass shader:

Now the sky shader full:

Vertex:

Fragment: declares uniforms + SKY_COMMON functions + main:

Note: cameraPosition is a built-in uniform in ShaderMaterial.

skyColor(ro, rd, steps):

For the lake reflection, ro = vec3(wp.x, 1.0, wp.z), fine.

One concern: aurora() uses gl_FragCoord for jitter — in lake shader that's also available. OK.

uSteps as uniform int. Loop for(int i=0;i<40;i++){ if(i>=steps) break; ...}.

Let me now also handle "uSeedOff" vec2 uniform for randomization.

Wind uniform for smoke drift & snowfall: constant vec2(-1.0, 0.3) normalized-ish scaled.

Snowfall shader:

If gate=0, size 0 → not rasterized. Good. Also fade by distance? fine.

Note mod with negative: GLSL mod(x,y)=x-y*floor(x/y) → always positive for y>0. Good.

uCenter updated to camera.position each frame (x,z). y fixed 30 → box spans y -35..95 around 30; camera orbit at y 90 → snow visible above. For ice mode y=3 → snow spans -35..95 covers. OK.

Smoke shader similar stateless:

frag: soft circle gray #aab4c8. Blending normal, depthWrite false, transparent.

uOrigin = chimney top world pos.

Meteors JS:

Trail update: keep array of Vector3 length N; each frame: pop last, unshift pos.clone(); write into position attribute; color attribute: alpha_i = (1 - i/N)^2 * fade → store in color attr (LineBasicMaterial vertexColors uses rgb; alpha not supported per-vertex) — use color scaled by fade (additive blending → black = invisible). Good: colors from white*fade → dark blue.

Spawn geometry: origin on sphere r=1350: random azimuth φ, elevation el ∈ [18°, 60°]. dir: mostly horizontal tangent + downward component: tangent = normalize(cross(radial, up)) ± random + radial*(-0.25..-0.45). speed 650-950.

Click spawn: raycaster ray; intersect sphere r=1350 (far intersection): t = -b + sqrt(...)? Ray from camera o dir d; |o + t d| = 1350 → solve. o inside sphere → t = -o·d + sqrt((o·d)² - (|o|² - r²)). Take positive root. If dir.y < 0.03 → boost y to 0.1. Then meteor dir: perpendicular-ish random with downward bias.

Audio module:

Noise buffer helper: create once, reuse for multiple sources (separate AudioBufferSourceNodes can share buffer).

Update loop calls AudioSys.update(t) for chime scheduling (uses ctx.currentTime).

Volume slider sets master gain * mute state.

UI wiring: straightforward; each slider input → S.param + label update + uniform sync (uniforms read S each frame anyway for most; theme colors set on change).

Buttons: mode buttons set cameraMode + active class; pause toggles S.paused (stop uTime advance & controls? keep controls active; freeze time uniform & meteors & snow — simplest: don't advance simTime; use simTime for all shader uTime; dt for camera still real). Bloom toggle: bloomPass.enabled. Sound toggle: AudioSys.toggle. Photo: snapshot().

Presets apply multiple S values + sync UI controls.

Quality select: apply steps uniforms + pixel ratio.

Theme select: set uColA/B/C on sky & lake mats + aurora tint color for terrain.

Randomize (R): uSeedOff = vec2(rand100, rand100).

Hide UI (H): body.classList.toggle('ui-hidden').

Camera transition:

Modes:

• orbit: controls enabled; flyTo(orbitPos, target0).
• drone: controls disabled; per-frame: angle = t0.03; pos = (cos520, 150+60sin(t0.11), sin520); lookAt(0, 40, 0) → smooth via lerp of current lookAt point. Implement: desired pos/quat computed; camera.position.lerp(desired, 1-exp(-dt1.2)); quaternion slerp toward lookAt quat.
• ice: pos = (cos(a)55, 2.6+0.4sin, sin(a)55), a = t0.02; lookAt = pos + dir toward heading with elevation ~28°: look at point (cos(a+0.5)300, 320, sin(a+0.5)300)?? Simpler: lookAt fixed sky point above horizon in direction of travel: target = pos3 + up260 → camera.quaternion slerp.

On entering orbit mode, controls.target set to (0,30,0).

Resize: camera aspect, renderer.setSize, composer.setSize, bloom resolution auto.

Loading overlay: hide after first frame rendered (requestAnimationFrame after init → add class done).

Stats: fps + mode + draw calls (renderer.info.render.calls).

Edge cases: WebGL fail → show message? skip.

Now, the amount of code is large. Let me write it.

Also remember index.html update: insert new card after <!-- New demos are added here -->.

Card description: "A polar night under the northern lights — ray-marched volumetric aurora curtains ripple across a star field above a frozen lake that mirrors them in real time, ringed by procedural snowy peaks, spruce forest and a lone cabin with chimney smoke. Call shooting stars with a click, drift between orbit / drone / ice-level cameras, four color themes & weather presets, synthesized wind/chime/whoosh WebAudio, bloom, quality scaling, PNG snapshots and keyboard shortcuts."

Title: "Aurora Borealis". Folder 015-aurora-borealis. Num 015.

Now write the demo file. I'll be very careful with syntax. Let me draft the entire file content now.

Structure:

CSS: adapt from 014 with aurora colors (green/purple gradient). IDs: stage, loading, title-panel, hint, controls, stats, plus buttons: mode-orbit, mode-drone, mode-ice, btn-pause, btn-bloom, btn-audio, btn-snap, btn-meteor, sliders: s-intensity, s-speed, s-density, s-stars, s-snow, s-bloom, s-volume with val spans *-v; selects: sel-theme, sel-quality; preset buttons: p-quiet, p-storm, p-crimson, p-freeze.

Let me carefully write the JS now. I'll write it in full here mentally and then output.

State:

Themes:

Shared uniforms object so all materials share:

GLSL common chunk:

Wait — moon disc: angular radius: cos threshold 0.99965 → angle ≈ 0.0265 rad ≈ 1.5° — big-ish but fine (stylized). muv divide by 0.024 maps disc to ~unit circle. OK.

Note: moon halo pow(c,900) — c near 1 only. fine.

Star cell 230 → stars dense; step(1-uStarAmt0.5, h) keeps fraction uStarAmt0.5 of cells... with starAmt 0.8 → 40% of cells have a star — too dense? cell angular size = 1/230 rad ≈ 0.25° → sky hemisphere ~ 2π sr; cells per sr ≈ 230² ≈ 53k → hemisphere ~330k cells * 40% = 130k stars — way too dense visually? Each star is sub-pixel mostly; smoothstep(0.10,0,d) in cell units — star radius 0.1 cell ≈ 0.025° ≈ ~1px at 1080p with fov 58 (0.054°/px... actually 58°/1080 ≈ 0.054°/px) → star diameter 0.05° ≈ 1px. 130k 1-px stars over ~2M px sky → 6% coverage — dense but stars are dim (mag^3 weighting → most dim). Might be OK but let me increase cell size to 140 and gate harder: step(1-uStarAmt*0.28, h). 140² = 19.6k cells/sr → 123k hemisphere * 22% = 27k stars. Reasonable. Star radius 0.10 cell → 0.041° ≈ 0.8px. OK.

Also add a few bright stars: mag pow 3 * 2.6 handles brightness range.

Aurora tuning sanity: dt for steps 34 over slab thickness along ray: vertical ray: t1-t0 = 390 → dt ≈ 11.5. d up to ~ band(≤1)rays(≤1)mask(≤1)hp(≤1)density(1) ≈ 1 typical max maybe 0.5. sum += dcoldt0.03intensity ≈ 0.511.50.03 ≈ 0.17 per step * 20 effective steps ≈ 3.4 * col(≤2 with edge) → could blow out to ~5+ → ACES will roll off; bloom will glow. Maybe too hot; but trans decreases. I'll scale 0.022. Hard to perfectly tune blind; choose 0.024 and intensity default 0.9. Also clamp final aurora to reasonable: sum = min(sum, vec3(6.0))? skip, ACES handles.

Terrain JS height:

Simple JS noise:

smooth(a,b,x) = smoothstep. Check center: r=0 → m=0 → h = 0 + 0 - 8.5 → -8.5. Lake at y=0.35 covers. r=200: m=smooth(165,430,200)=~0.07 → h ≈ 0.07*(~160 avg? ridged avg ~0.45330≈150+26=176 → 12) - 8.5(1-smooth(40,250,200)=1-0.79=0.21 → -1.8) + 2.2smooth(150,235,200)=2.20.62=1.37*(1-smooth(235,420,200)=1) → ≈ 12 - 1.8 + 1.4 ≈ 11.6?? That's above lake 0.35 at r=200 — but lake radius 190 → shoreline at ~190. r=190: m=smooth(165,430,190)=0.033 → ~5.8 - 8.5*(1-0.68)=−2.7 + 2.20.47=1.03 → ≈ 4.1 > 0.35. Hmm shoreline inside lake radius → lake edge buried under terrain at r=190 (terrain 4m above lake plane). The lake circle radius 190 would be under terrain near its rim → z-fighting/hidden edge. Fix: make lake radius 175 and ensure terrain at r<175 is below 0.35: r=170: m=smooth(165,430,170)=0.001 → ~0.2; -8.5(1-smooth(40,250,170)=1-0.62=0.38)= -3.2; +2.2smooth(150,235,170)=2.20.28=0.62 → ≈ -2.4 < 0.35 ✓. r=175: m≈0.005→0.9; -8.5*(1-0.655)= -2.9; +2.20.31=0.68 → -1.3 ✓. r=185: m=0.02→3.5; -8.50.31= -2.6; +2.2*0.39=0.86 → 1.76 > 0.35 → shore between 175 and 185. Lake radius 176 → rim intersects terrain around r≈178-182 — terrain rises through lake plane → natural shoreline.

But wait — the shelf term +2.2*smooth(150,235,r) creates a berm ring; fine.

Cabin at (168,-148): r = 224 → terrain there: m=smooth(165,430,224)=0.13 → 0.13176≈23 + detail − 8.5(1-0.83)=−1.4 + 2.20.79(1-0)=1.74 → ≈ 23.5. Then cabin pad lerps to 3.2 within 12-30m. Cabin base at y=3.2. OK — cabin sits on a flattened pad on a hillside above the lake. Good. Trees must avoid cabin pad: skip if dc < 26.

Lake: CircleGeometry(176, 72) rotated -90° x, y=0.35.

Terrain geometry: PlaneGeometry(2600, 2600, 256, 256) → 65k vertices fine. rotateX(-PI/2) then displace y = terrainH(x,z). computeVertexNormals.

Terrain shader:

Note floor(vW7.0) — vW up to 13007=9100; hash13 fract-based stable to ~1e5. OK.

Terrain fragment needs noise2/hash13 → include GLSL_COMMON (which declares aurora uniforms too — unused but fine; must provide those uniforms in material — share U anyway).

Lake shader:

Reflection of aurora in ice — the money shot. ✓

Trees:

Cone normals: flatShading in material gives faceted look. vertexColors with flatShading OK.

InstancedMesh count ~650. Per instance: matrix compose(pos, quatY(rot), scale). Also instanceColor slight tint variation? With vertexColors + instanceColor both multiply — fine, subtle variation 0.85-1.1 gray. Skip instanceColor to keep simple.

Placement loop: attempts 4000, accept ~650: r = 185 + pow(rand,0.7)760; θ rand; h=terrainH; accept if h>1.2 && h<240; slope via finite diff: (terrainH(x+3,z)-h)/3 etc → accept if |grad| < 0.75; forest mask fbmJS(x0.004, z*0.004) > 0.42 → clumps; avoid cabin dc>26; avoid center.

Scale: s = 0.8 + rand*1.1; y = h - 0.15.

Cabin build:

Also a few trees + a wood pile near cabin? skip.

Smoke origin: chimney top world: cabin pos + rotated (2.6, 7.6, 1.4). Compute via cabin.localToWorld. Do after adding to scene & updateMatrixWorld.

Mist: canvas radial texture (shared with meteor head & halo — make glowTexture() helper returning CanvasTexture radial white→transparent). Sprites: color 0x8fa8cc, opacity 0.05-0.1, scale (90-160, 24-40), positions r<160 on lake y 2-7. Drift: store phase; update pos.x = base + sin(t*0.02+φ)*20 etc.

Meteors: as designed. Trail: 22 points.

Meteor head: Sprite with glow texture, color 0xcfe4ff, scale 18. Additive.

Spawn:

randomSkyPoint: az = rand2π; el = 0.35+rand0.75 rad (20°-63°); pos = (cos az * cos el, sin el, sin az * cos el)*1350.

Auto-spawn timer: next = now + (3 + rand*6)/S.meteorRate.

Click: on pointerdown without drag (track movement < 5px) → raycast → spawnMeteor(pointOnSphere). Also only when clicking sky (not UI — canvas listener fine).

Point on sphere along ray: solve |o+td|=1350: b=o·d; c=o·o−1350²; t = −b + sqrt(b²−c). If NaN (shouldn't, camera inside) skip. If point.y < 60 → set spawn from that direction anyway but clamp el.

Grade pass:

Composer: RenderPass, bloomPass = new UnrealBloomPass(new Vector2(innerWidth, innerHeight), S.bloomStr, 0.55, 0.6), OutputPass, gradePass.

Hmm — grain after OutputPass operates in sRGB — fine.

Camera modes update in loop:

Simplify: for drone/ice, controls.enabled=false and every frame we directly drive camera with lerp factor k = 1 - exp(-dt*1.6) toward desired pos/quat — gives smooth transitions automatically without explicit tween state. For orbit: controls.enabled=true; on switch to orbit, set camera toward default via same lerp until close then hand over? OrbitControls fights lerp. Approach: when switching to orbit, set controls.target to (0,40,0) and let user control from wherever camera currently is — no flyback needed (smooth enough since orbit just continues from current pose). Nice and simple.

Drone desired:

Look toward lake center mostly: look = (0, 55, 0). But then aurora out of view half the time? Aurora fills sky above horizon everywhere (mask patches) — looking horizontally at center from 170 height shows sky upper half. FOV 58 → ok. Slight look up: look = (0, 130, 0)? Then terrain barely visible. Compromise look y=90.

Ice mode:

Quaternion: build temp matrix lookAt(pos, look, up) → quaternion; slerp.

Pause: freeze simTime advance; meteors update with dt=0 effectively; snow uses uTime → frozen; camera still moves (uses real dt for lerp, simTime for path → frozen path too — acceptable: pause freezes world; orbit still works).

Actually for pause, keep controls responsive — yes since orbit uses controls.

Keyboard: keydown handler: '1','2','3' modes; ' ' pause toggle (preventDefault scroll); 'b' bloom; 'm' sound; 'p' photo; 'h' UI; 'r' reseed; 'n' meteor now.

Snapshot:

composer.render() then toDataURL same tick — works.

Stats: fps EMA + renderer.info.render.calls + mode.

Loading overlay: after first composer.render, add 'done'.

Resize handler.

Audio implementation details:

Note: connecting lfo3G to whGain.gain with base 0 → whistle gain oscillates 0±0.018 — negative gain = phase invert, fine (inaudible diff). OK.

Master gain scaling: S.volume 0..1 → *0.9.

UI HTML:

I'm at 92% of max time already?! timeProgress 0.92 — that's concerning. I need to move fast. Wait, this says "maxTime" threshold 50%, timeProgress 0.9216 — meaning 92% of time budget consumed. I must finish quickly. Let me write the remaining JS in as few appends as possible — ideally one big append, then quick validation, then index update, then success.

Let me write the entire remaining JS in one heredoc append. Keep it tight but complete. I'll write carefully.