# Bubble Chamber — Design Notes

A parametric generator for artificial bubble-chamber plates, aimed at
large-format B&W print. Deterministic from a seed string; tweakable in the
browser; exportable as photographic raster (full analog texture) or clean
vector (SVG/PDF) for print.

The north star is a worn CERN-era plate: a photographic *positive* (dark ink
on milky paper), busy with multi-scale tracks, dozens of tight δ-ray spirals,
a dramatic pressure/shock disk, and the analog remnants of a real plate — film
grain, uneven development, scratches, dust, water rings.

## Core architecture — one scene, many renderers

```
seed ──► generateScene(params)  ──┬─► renderCanvasPhoto()  photographic raster (preview + hi-res PNG)
         (pure data, no DOM)      ├─► renderSVG()          clean vector for print
                                  └─► buildPDF()           vector PDF (24" page)
```

`generateScene()` returns a **renderer-agnostic data model** — tracks (as
polylines of `{x,y,beta,theta}`), the shock disk, plate artifacts, plus derived
metadata (hash, plate number). Every renderer consumes exactly this. This is the
seam to preserve: physics/geometry never touches a drawing API.

Bubble *positions* are sampled by the shared `sampleBubbles()` using a salted
RNG (`makeRng(seed,'bubbles')`), so the raster and vector outputs place bubbles
identically. Only the *look* differs between renderers.

Coordinates are a logical `[-1,1]` square; renderers map to whatever pixel size
they need. Effect radii in the raster renderer scale with output size, so the
live preview (1000px) and the print render (5400px+) look the same.

## Files

```
src/
  rng.js              cyrb53 hash, mulberry32 PRNG, salted streams, distributions
  scene/
    scene.js          generateScene() — assembles events, cosmics, shock, artifacts
    track.js          trajectory integrator (B-field + energy loss), momentum sampling, cosmics
    delta.js          δ-ray log-spirals (the curly bits)
    vdecay.js         neutral-decay "V" daughters
    shock.js          pressure/shock disk model
    instrument.js     chamber optics: structural fan lines, chords, wall arcs
    media.js          physical-artifact & human layer: grease-pencil marks, film
                      furniture (sprockets/data box/edge text), réseau grid, splice
    artifacts.js      plate damage: scratches, hairs, dust, rings, fingerprints
    params.js         derive a full tasteful parameter set from a seed (archetypes)
    bubbles.js        polyline → bubbles (shared by all renderers)
  render/
    canvasPhoto.js    photographic multi-pass raster compositor
    svgVector.js      clean vector renderer
    pdf.js            minimal vector PDF writer
    palette.js        pluggable colour "feels" (registry; mono/charge/β + extensible)
    noise.js          value-noise / fbm for grain + tonal mottle
  ui/controls.js      declarative control + preset config (single source)
  main.js             panel build, state, render loop, exports
  style.css
index.html            dev entry (ES modules; needs a static server)
build.mjs             zero-dep bundler → single-file bubble_chamber.html (file://-openable)
tools/
  preview.html        headless render harness (artwork only, params via URL query)
  shoot.sh            build+screenshot helper for the visual compare loop
  render-svg.mjs      CLI SVG render (--seed mode or legacy preset; shares scene module)
  render-pdf.mjs      CLI PDF render (print-ready CMYK; --seed mode)
  inspire.sh          randomize seeds → seed-named thumbnails + HTML contact sheet
  render.sh           one seed → print masters (SVG + PDF + hi-res PNG)
  gallery.sh          render the curated preset set
```

## Seed-driven workflow (large format)

`paramsFromSeed(seed)` makes the seed the complete fingerprint of a plate, so a
thumbnail and its print master are identical. Browse `tools/inspire.sh` output,
then `tools/render.sh <SEED>` for masters. The full large-format strategy
(vector geometry + raster texture layers, resolution math, assembly) is in
**PRINT.md**. Headless PNG ceiling ≈ 14000 px; SVG/PDF are resolution-independent.

## Physics & geometry decisions

- **Trajectory**: charged particle in a uniform out-of-page B field curves with
  radius `r = p/(qB)`. Energy loss `dp/ds ∝ 1/β²` (simplified Bethe-Bloch) shrinks
  `p`, tightening the radius toward end-of-range — the inward spiral. The
  integrator *shortens its step in tight curvature* (`MAX_DTHETA`) so terminal
  spirals stay smooth instead of going polygonal.
- **β as the master variable**: tracked along every polyline; drives both bubble
  density (`∝1/β²`) and bubble radius (fatter as β falls). Get the β statistics
  right and the image reads as authentic regardless of rendering tricks.
- **Momentum** is log-normal (heavy-tailed): most tracks moderate, a real tail of
  very stiff (long, near-straight) and very soft (tight spirals).
- **δ-rays** are modelled directly as **logarithmic spirals** (radius decays
  exponentially with wind angle) rather than integrated down to sub-percent
  radii. This converges cleanly to a point and reliably reads as the textbook
  curl. β falls toward the centre so the curl gets denser and fatter inward.
- **Cosmics/transients**: very stiff tracks entering from the frame edge, crossing
  as near-straight diagonals (the long lines in real plates that ignore the vertex).
- **Shock disk**: not physics — a chamber/window pressure artifact. Modelled as a
  dark annulus body with a bright textured centre, a hard rim, and fine striations
  that burst *outward* from a ring. The strongest compositional anchor.
- **Depth & exposure** (Phase 1): the chamber is a volume photographed with finite
  depth of field. Every track carries a depth `z` (0 = focal plane) and an `age`
  (0 = current trigger); one interaction's tracks fan out across a range of z.
  `depthFactors(track, params)` maps these — with the `depth` and `aging` dials —
  to **tone** (opacity), **sizeScale**, and **softness**. Softness folds into one
  continuous value with the global **`bubbleSoft`** edge-softness dial and drives
  the raster sprite's gradient (`bubbleStops`, shared with the SVG bubble
  gradient so raster/vector match) and footprint. Variation is depth/time-driven, not noise, so
  it reads as a 3D volume and a temporal palimpsest. Density (ionisation) is left
  to β; depth only touches opacity/size/softness. Applies in raster *and* vector.

## Colour palettes (Phase 2)

Colour is an optional, swappable **"feel"** layered on the geometry — **B&W is the
default** (`palette: 'mono'`). `palette.js` is a registry; each entry maps the
scene's physics to colour via optional hooks: `ink(track,env)` (per-trail colour),
`paper(env)`, `feature(env)` (non-particle marks), `vign(env)`. Adding a feel is
one entry. `resolvePalette(id, env)` fills defaults so renderers stay simple.
Shipped: `mono`, `charge` (duotone by charge sign), `beta` (velocity → spectral),
and `lifecycle` (per-bubble: colour follows each particle birth→death). Two hook
levels: `ink(track,env)` for per-track colour, and `bubbleInk({track,life,beta},env)`
for **per-bubble** colour — `sampleBubbles` tags every bubble with `life` (0=birth
at the vertex, 1=death/rest) and local `beta`. `resolvePalette` exposes `perBubble`
so renderers stamp a colour-keyed sprite per-track (fast) or per-bubble (quantised,
still bounded). SVG emits a gradient per distinct colour, PDF uses RGB for trails
(mono stays CMYK rich black). Track attributes for mappings: `q` (charge),
`pts[i].beta`, `kind`, `weight`, `z`, `age`. Colour is render-only and orthogonal
to geometry, so any seed re-colours without changing its forms.

Also shipped: `kind` (one categorical hue per particle type — primary/δ-ray/cosmic/
sweeper/V-decay), `kindlife` / `kindrise` (type sets the hue, lifecycle sets the
*intensity* — fading toward, or rising into, the death), `psychedelic` (per-bubble
hue cycles, `hueCycles`), `cyanotype` (a full chemistry: overrides `paper()` + ink
for the blueprint look), and `magentarise` (a **sweepable two-colour relationship**: a trace family by type +
rising intensity + a monochrome contrasting disk via `feature()`). Its pairing is
parameterised by three dials — **`traceHue`** (offset that rotates the whole trace
family while keeping the by-type spread), **`diskHue`** and **`diskSat`** (the
disk/feature accent, deliberately *not* touched by global hue-shift/saturation so it
reads as an independent second colour). Defaults (0 / 0.06 / 0.82) reproduce the
original magenta-vs-burnt-orange exactly. A palette is one registry entry; hooks:
`ink`/`bubbleInk`/`paper`/`feature`/`vign`.

**Saturation** is a global `saturation` dial applied in `resolvePalette` (about
each colour's own luminance: 0 = grey, 1 = as-authored, >1 boosted), and
**`hueShift`** rotates every palette's hues (CSS hue-rotate matrix; greys are
unchanged so mono stays B&W) — both ink-only, substrate untouched.

Because a palette may set a dark ground (cyanotype), the raster renderer chooses
its ink **blend mode from the actual paper luminance** (`pal.darkGround()`) rather
than the `invert` flag — so light-on-dark chemistries composite correctly. For
`mono` this is identical to the old invert-based behaviour.

**Paper toning & shading** is a *separate* system from the ink palette
(`paperTone(params, inv)`): a photographic toner (`paperTone` select — cream /
sepia / selenium / cool / olive / neutral, as tint multipliers relative to cream),
`toneStrength`, `paperBright`, and `glow` (gas-glow gradient strength). It feeds
the renderers' base paper + vignette tint, so any ink palette pairs with any paper
(e.g. sepia substrate under lifecycle trails). Defaults (cream / 1 / 1 / 0.5)
reproduce the committed look exactly. A palette may still fully override `paper()`
for a complete "chemistry" feel (e.g. a future cyanotype).

## The analog (raster) layer

`renderCanvasPhoto` is a multi-pass compositor:

1. paper fill + radial gas-glow gradient
2. low-frequency tonal mottle (fbm noise, multiply) — uneven development/illumination
3. ink layer (offscreen): faint continuity under-stroke per track + soft blooming
   bubbles stamped from a cached radial-gradient sprite (overlaps merge into lines)
4. halation/bloom: a blurred copy of the ink composited back for soft spread
5. sharp ink composited onto paper (`multiply` for the positive look)
6. plate damage (dark via multiply; some scratches *lift* via screen)
7. fiducials + chamber boundary
8. vignette
9. structured film grain (supra-pixel clumps, overlay blend)

Grain/mottle/bloom are intentionally **raster-only**. The vector renderer is the
clean graphic version (soft bubbles via a shared radial-gradient fill, no grain).

## Reproducibility

Everything is seeded. New stochastic subsystems must follow the salt pattern:
`makeRng(seed, 'subsystem')`. That's what lets a parameter tweak change one thing
without reshuffling the rest of the plate.

## Build / run

- **Tweak interactively**: `node build.mjs` then open `bubble_chamber.html`
  directly (no server needed — it's a single self-contained file). Or for live
  module editing, serve the folder (`python3 -m http.server`) and open `index.html`.
- **Visual compare loop**: `tools/shoot.sh /tmp/out.png "preset=BEBC%20Archival&size_px=1200"`
  renders the artwork headlessly via Chrome. Any param can be set in the query.
- **Offline SVG / PDF**: `node tools/render-svg.mjs "BEBC Archival" SEED out.svg`
  and `node tools/render-pdf.mjs "BEBC Archival" SEED out.pdf`.

> Tip for iteration: drop the target reference image into `reference/` so it can
> be opened side-by-side with renders when tuning toward it.

## Print pipeline (done)

- **PDF**: DeviceCMYK (warm cream + rich black), per-element alpha via ExtGState
  (`/ca`,`/CA`), Helvetica archival header. 24″ page (1728pt). Validated against
  macOS's native Quartz renderer.
- **PNG**: 7200px (24″ @ 300 DPI), full film texture; effect radii scale with size.
- **SVG**: 4800px clean vector with header + soft-bubble gradients.
- **Archival metadata** (lab, plate no., exposure date) derives deterministically
  from the seed, so any export is reproducible and self-labelling.

## Open threads / next ideas

- **Tune toward the reference** — once it's in `reference/`, a side-by-side pass on
  density / curl abundance / track weight / tonality.
- **Stereo pairs** — two offset views from one seed, as a diptych.
- **Plate series** — deterministic MUON-001…024 grid (archival-sheet aesthetic).
- **16-bit / TIFF** export for the highest-end print path (browser PNG is 8-bit).
- **Colour stretch goal** — map charge or β to a channel for a stylized variant.
- **Performance** — the 7200px PNG does heavy per-bubble stamping + blur; a WebGL
  post stage (grain/bloom/blur) would make hi-res renders near-instant.
```