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DESIGN.md
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DESIGN.md
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# Bubble Chamber — Design Notes
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A parametric generator for artificial bubble-chamber plates, aimed at
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large-format B&W print. Deterministic from a seed string; tweakable in the
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browser; exportable as photographic raster (full analog texture) or clean
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vector (SVG/PDF) for print.
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The north star is a worn CERN-era plate: a photographic *positive* (dark ink
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on milky paper), busy with multi-scale tracks, dozens of tight δ-ray spirals,
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a dramatic pressure/shock disk, and the analog remnants of a real plate — film
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grain, uneven development, scratches, dust, water rings.
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## Core architecture — one scene, many renderers
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```
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seed ──► generateScene(params) ──┬─► renderCanvasPhoto() photographic raster (preview + hi-res PNG)
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(pure data, no DOM) ├─► renderSVG() clean vector for print
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└─► buildPDF() vector PDF (24" page)
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```
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`generateScene()` returns a **renderer-agnostic data model** — tracks (as
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polylines of `{x,y,beta,theta}`), the shock disk, plate artifacts, plus derived
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metadata (hash, plate number). Every renderer consumes exactly this. This is the
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seam to preserve: physics/geometry never touches a drawing API.
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Bubble *positions* are sampled by the shared `sampleBubbles()` using a salted
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RNG (`makeRng(seed,'bubbles')`), so the raster and vector outputs place bubbles
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identically. Only the *look* differs between renderers.
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Coordinates are a logical `[-1,1]` square; renderers map to whatever pixel size
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they need. Effect radii in the raster renderer scale with output size, so the
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live preview (1000px) and the print render (5400px+) look the same.
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## Files
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```
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src/
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rng.js cyrb53 hash, mulberry32 PRNG, salted streams, distributions
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scene/
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scene.js generateScene() — assembles events, cosmics, shock, artifacts
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track.js trajectory integrator (B-field + energy loss), momentum sampling, cosmics
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delta.js δ-ray log-spirals (the curly bits)
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vdecay.js neutral-decay "V" daughters
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shock.js pressure/shock disk model
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instrument.js chamber optics: structural fan lines, chords, wall arcs
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artifacts.js plate damage: scratches, hairs, dust, rings, fingerprints
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params.js derive a full tasteful parameter set from a seed (archetypes)
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bubbles.js polyline → bubbles (shared by all renderers)
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render/
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canvasPhoto.js photographic multi-pass raster compositor
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svgVector.js clean vector renderer
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pdf.js minimal vector PDF writer
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noise.js value-noise / fbm for grain + tonal mottle
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ui/controls.js declarative control + preset config (single source)
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main.js panel build, state, render loop, exports
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style.css
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index.html dev entry (ES modules; needs a static server)
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build.mjs zero-dep bundler → single-file bubble_chamber.html (file://-openable)
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tools/
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preview.html headless render harness (artwork only, params via URL query)
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shoot.sh build+screenshot helper for the visual compare loop
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render-svg.mjs CLI SVG render (--seed mode or legacy preset; shares scene module)
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render-pdf.mjs CLI PDF render (print-ready CMYK; --seed mode)
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inspire.sh randomize seeds → seed-named thumbnails + HTML contact sheet
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render.sh one seed → print masters (SVG + PDF + hi-res PNG)
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gallery.sh render the curated preset set
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```
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## Seed-driven workflow (large format)
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`paramsFromSeed(seed)` makes the seed the complete fingerprint of a plate, so a
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thumbnail and its print master are identical. Browse `tools/inspire.sh` output,
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then `tools/render.sh <SEED>` for masters. The full large-format strategy
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(vector geometry + raster texture layers, resolution math, assembly) is in
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**PRINT.md**. Headless PNG ceiling ≈ 14000 px; SVG/PDF are resolution-independent.
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## Physics & geometry decisions
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- **Trajectory**: charged particle in a uniform out-of-page B field curves with
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radius `r = p/(qB)`. Energy loss `dp/ds ∝ 1/β²` (simplified Bethe-Bloch) shrinks
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`p`, tightening the radius toward end-of-range — the inward spiral. The
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integrator *shortens its step in tight curvature* (`MAX_DTHETA`) so terminal
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spirals stay smooth instead of going polygonal.
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- **β as the master variable**: tracked along every polyline; drives both bubble
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density (`∝1/β²`) and bubble radius (fatter as β falls). Get the β statistics
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right and the image reads as authentic regardless of rendering tricks.
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- **Momentum** is log-normal (heavy-tailed): most tracks moderate, a real tail of
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very stiff (long, near-straight) and very soft (tight spirals).
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- **δ-rays** are modelled directly as **logarithmic spirals** (radius decays
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exponentially with wind angle) rather than integrated down to sub-percent
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radii. This converges cleanly to a point and reliably reads as the textbook
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curl. β falls toward the centre so the curl gets denser and fatter inward.
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- **Cosmics/transients**: very stiff tracks entering from the frame edge, crossing
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as near-straight diagonals (the long lines in real plates that ignore the vertex).
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- **Shock disk**: not physics — a chamber/window pressure artifact. Modelled as a
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dark annulus body with a bright textured centre, a hard rim, and fine striations
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that burst *outward* from a ring. The strongest compositional anchor.
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## The analog (raster) layer
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`renderCanvasPhoto` is a multi-pass compositor:
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1. paper fill + radial gas-glow gradient
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2. low-frequency tonal mottle (fbm noise, multiply) — uneven development/illumination
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3. ink layer (offscreen): faint continuity under-stroke per track + soft blooming
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bubbles stamped from a cached radial-gradient sprite (overlaps merge into lines)
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4. halation/bloom: a blurred copy of the ink composited back for soft spread
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5. sharp ink composited onto paper (`multiply` for the positive look)
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6. plate damage (dark via multiply; some scratches *lift* via screen)
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7. fiducials + chamber boundary
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8. vignette
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9. structured film grain (supra-pixel clumps, overlay blend)
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Grain/mottle/bloom are intentionally **raster-only**. The vector renderer is the
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clean graphic version (soft bubbles via a shared radial-gradient fill, no grain).
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## Reproducibility
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Everything is seeded. New stochastic subsystems must follow the salt pattern:
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`makeRng(seed, 'subsystem')`. That's what lets a parameter tweak change one thing
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without reshuffling the rest of the plate.
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## Build / run
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- **Tweak interactively**: `node build.mjs` then open `bubble_chamber.html`
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directly (no server needed — it's a single self-contained file). Or for live
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module editing, serve the folder (`python3 -m http.server`) and open `index.html`.
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- **Visual compare loop**: `tools/shoot.sh /tmp/out.png "preset=BEBC%20Archival&size_px=1200"`
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renders the artwork headlessly via Chrome. Any param can be set in the query.
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- **Offline SVG / PDF**: `node tools/render-svg.mjs "BEBC Archival" SEED out.svg`
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and `node tools/render-pdf.mjs "BEBC Archival" SEED out.pdf`.
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> Tip for iteration: drop the target reference image into `reference/` so it can
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> be opened side-by-side with renders when tuning toward it.
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## Print pipeline (done)
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- **PDF**: DeviceCMYK (warm cream + rich black), per-element alpha via ExtGState
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(`/ca`,`/CA`), Helvetica archival header. 24″ page (1728pt). Validated against
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macOS's native Quartz renderer.
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- **PNG**: 7200px (24″ @ 300 DPI), full film texture; effect radii scale with size.
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- **SVG**: 4800px clean vector with header + soft-bubble gradients.
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- **Archival metadata** (lab, plate no., exposure date) derives deterministically
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from the seed, so any export is reproducible and self-labelling.
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## Open threads / next ideas
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- **Tune toward the reference** — once it's in `reference/`, a side-by-side pass on
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density / curl abundance / track weight / tonality.
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- **Stereo pairs** — two offset views from one seed, as a diptych.
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- **Plate series** — deterministic MUON-001…024 grid (archival-sheet aesthetic).
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- **16-bit / TIFF** export for the highest-end print path (browser PNG is 8-bit).
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- **Colour stretch goal** — map charge or β to a channel for a stylized variant.
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- **Performance** — the 7200px PNG does heavy per-bubble stamping + blur; a WebGL
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post stage (grain/bloom/blur) would make hi-res renders near-instant.
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```
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