A $10,000 website is free — if you know exactly what to ask.

# Kōrei (raymarched SDF dreamscape)

Build a single self-contained `index.html`: a contemplative full-screen
dreamscape — floating stones and a half-submerged ring gate over a still
sea — rendered entirely by one WebGL2 fragment shader. No 3D models, no
libraries, no textures: every pixel is computed by raymarching signed
distance fields. Beneath the canvas, a short essay explains the technique
in plain language. Tone: quiet, Japanese-garden minimalism.

## Fonts and palette

Google Fonts: **Shippori Mincho** (500/600) for display, **Inter**
(400/500) for UI and body.

- night `#0c111f`, ink `#e9ecf5`, muted `#9aa3b8`, hairline `#232c42`,
  focus ring `#9db7ff`, hero subtitle `#c3cbdd`

Three light moods as shader uniform sets (RGB floats), eased toward at
0.045 per frame so switching feels like weather, not a toggle:

- **Dawn** — skyTop (.545,.639,.831), horizon (.949,.796,.659), sun
  (1,.863,.722), water (.145,.196,.318), stone (.271,.302,.373), sun
  direction (-.34,.20,.92), no stars.
- **Dusk** — skyTop (.357,.329,.533), horizon (.910,.624,.553), sun
  (1,.616,.463), water (.129,.129,.251), stone (.243,.227,.310), sun
  direction (.42,.12,.90) — the light swings to the other side.
- **Night** — skyTop (.043,.063,.157), horizon (.153,.200,.353), moonlit
  sun (.863,.902,1), water (.047,.071,.149), stone (.137,.165,.239), sun
  direction (-.26,.38,.89), stars ON (hash a `floor(rd*260)` grid,
  `step(0.9975, …)`, brightness faded near the horizon).

## The hero technique (name it honestly on the page)

One WebGL2 program drawn as a single fullscreen triangle — no vertex
buffers; derive the corners from `gl_VertexID`:
`vec2 v = vec2(float(gl_VertexID<<1&2), float(gl_VertexID&2))*2.0-1.0;`
which yields (-1,-1)(3,-1)(-1,3). (The naive ±1 version covers only half
the screen — a classic bug; verify a full-frame render.)

Scene SDF (`map`):
- **Seven floating stones** — spheres placed on a golden-angle spiral
  (`ang = i*2.39996`, radius `1.7+1.7*hash(i)`), radii `0.26+0.30*hash`,
  squashed vertically (`q.y *= 1.22`), each bobbing slowly
  (`y += 0.16*sin(t*0.35 + i*1.7)`), all blended with a **smooth minimum**
  (k = 0.42) so near stones melt together like wet clay.
- **The gate** — a vertical torus at (0, 0.55, 7.2), major radius 2.35,
  tube 0.20, standing half in the sea.

Rendering per pixel:
- **Sphere tracing**: 92 steps desktop / 70 on small screens, hit epsilon
  scaled by distance (`d < 0.0012*s`), far plane 55.
- The **sea is an analytic plane** (y = 0): intersect by division, not
  marching. Ripples only perturb the shading normal (two crossed sine
  waves, amplitude 0.013).
- **Soft shadows**: a second march toward the sun, penumbra from
  `min(res, 9*d/s)`, up to 24 steps.
- **Reflections**: reflect the ray at the water, march again (up to 40
  steps); mix with sky by fresnel (`0.06 + 0.94*(1-cosθ)^5`); add sun
  glitter `pow(dot(refl, sun), 700)` gated by the shadow term.
- Normals by central differences (tetrahedron trick, e = 0.0015).
- Stone shading: diffuse×shadow, ambient from `0.5+0.5*n.y`, rim
  `(1-dot(n,-rd))^3`, Blinn-Phong speck (pow 48), sky-tint fill; distance
  fog `1-exp(-0.0022*t²)` toward the sky color.
- Finish: filmic-ish tonemap `col/(1+col)`, gamma 1/2.2, gentle vignette,
  ±0.007 hash film grain.

Camera: origin sways `0.42*sin(t*0.06)` at height 1.18, z −4.4; the
look-at target follows the pointer softly (±0.55 x, ±0.28 y) — parallax,
not control.

## Performance ladder (build all four rungs)

1. Full loop on real GPUs, `devicePixelRatio` capped at 1.5 (1.4 on small
   screens), rAF only, loop paused on `visibilitychange`.
2. Detect software rasterizers via `WEBGL_debug_renderer_info` (match
   /swiftshader|llvmpipe|softpipe|software/i) → render **one still frame**
   at half resolution with reduced step counts instead of looping.
3. `prefers-reduced-motion: reduce` → same still-frame mode; re-render
   once on mood change and resize (time frozen at t = 12).
4. No WebGL2 at all → remove the canvas, show a dignified text fallback
   panel. Also handle `webglcontextlost`/`restored`: pause, rebuild the
   program, resume; only surface a message if restore never comes (3 s).

## Layout, top to bottom

1. **Masthead** (absolute over the canvas) — wordmark "Kōrei"
   letterspaced .42em, right-side tagline "Rendered by distance".
2. **Stage** — 100svh canvas (`aria-label` describing the scene); a
   centered title block: "Kōrei" in Shippori Mincho
   `clamp(44px, 7vw, 84px)` plus the line "No 3D models. Every pixel is a
   distance, measured."; a top scrim
   (`linear-gradient(rgba(7,10,20,.52), transparent)`, top 38%) so text
   stays readable over the bright dawn sky.
3. **Mood pills** bottom-center — a `fieldset` legend "Light" and three
   buttons Dawn / Dusk / Night with `aria-pressed`, min-height 44px,
   translucent dark fill + `backdrop-filter: blur(6px)`.
4. **Essay** — heading "A landscape with no geometry", a lede, then three
   ruled columns: Distance fields / Sphere tracing / Light, twice more —
   each explaining its concept in two sentences, no jargon left undefined.
5. **Footer** — one line stating the whole landscape lives in one fragment
   shader; links to the build notes and the hub.

## Quality bar

Keyboard: moods are real `button`s with visible `:focus-visible` outlines
(3px, `#9db7ff`). AA contrast everywhere (the scrim is what buys it on the
hero). No horizontal scroll; fully usable and composed at 390px (fewer
march steps + lower DPR there). Honest copy: never claim models or assets
— the point of the page is that there are none.