8defef3ed0
A failed shader compile renders black, and black frames are identical to each other, so every block scores 0.000 and the row reads as the least varied scene in the library rather than as a broken one. That happened yesterday — the subject helpers were declared above the ink they call, GLSL has no forward declarations, the whole preamble failed to compile, and the gallery reported a variety of exactly 0.000 with no indication anything was wrong. It is a particularly bad failure mode for a tool whose entire job is ranking scenes by that number. A scene whose first frame has no luminance and no variance is now reported as broken, with both figures and a pointer to the console, and the row is coloured apart from the merely flat ones so it cannot be mistaken for a bad score. The summary counts them separately. Verified against both answers rather than only the happy one: a healthy Moiré Grid comes back 0.0365 with no error, and a deliberately broken copy of the same scene comes back with the diagnosis instead of a zero. Recorded in HOWTO-variety.md alongside the other instrument traps, since the general lesson outlives this instance — a broken render produces the most boring possible numbers rather than an error. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
254 lines
11 KiB
Markdown
254 lines
11 KiB
Markdown
# How to build a visualizer that varies
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`HOWTO-visualizers.md` covers making a scene that *works*. This one covers making
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a scene that looks different from one song to the next — a separate skill, and
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the one the library is currently worst at.
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Everything here is a measurement rather than an opinion, and the numbers are
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quoted so a future change can contradict them. Several already contradict things
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believed earlier in the same week. Living document: add what you learn, and
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delete what stops being true.
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---
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## The one-line version
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> A scene varies when the SONG can change what is on screen. It does not vary
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> because its parameters moved.
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Parameters mostly change the same picture. Content changes the picture.
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---
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## How to know if you succeeded
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```
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gallery.html your scene, six times, on six songs — with a score
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checks.html?scene=X the per-scene gate, including `consumes:` lines
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```
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The gallery score is the mean structural distance between a scene's own six
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frames, on the same descriptor the variety harness uses. **Minimum bar: 0.04**
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(`MIN_VARIETY` in `checks/gallery.js`), drawn as a red line. Below it a scene is
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the same picture wherever it appears, and because it is cast into many songs
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that sameness leaks between them — the viewer recognises the shot rather than
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the song.
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Some reference points, measured:
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```
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0.219 Droste Feedback varies a lot
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0.181 Spectrum Sculpture
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0.049 Isometric Blocks after work — see below
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0.039 Apollonian Gasket beautiful, and the same six times
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0.031 Moiré Grid the same picture in six palettes
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```
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---
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## What the descriptor can and cannot see
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Design against this, because half of "why is my score low" is here.
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**It is blind to:**
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- **Brightness and contrast.** Frames are standardised to zero mean and unit
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variance before anything is measured. A scene that only gets brighter has not
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changed.
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- **Colour.** Measured, reported, and excluded from the score. Six palettes
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cannot disguise one image, which was the entire point.
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- **Rotation**, on the scale, orientation and texture blocks.
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- **Quality.** It measures change between songs, nothing else. Apollonian Gasket
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scores 0.039 and looks great. Both facts are true and neither implies the
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other.
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**It sees:**
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| block | what it measures | how to move it |
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|---|---|---|
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| `scale` | feature size — fine grain vs large forms | let the song set element size (`stageScale()`) |
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| `orient` | grid vs radial vs stripes, rotation-blind | break or vary a regular lattice |
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| `layout` | where in the frame structure sits | move the subject, change what is empty |
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| `texture` | element count, sparsity, mirror and radial symmetry | vary how many things there are |
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| `motion` | what moves and where, not how much | vary the KIND of movement, not the rate |
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**A known blind spot.** `layout` is nearly useless for full-frame fields. Voronoi
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Shatter measures 0.004 there no matter what changes, because edge-to-edge cells
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occupy the same frame however they fall. That is honest — there genuinely is no
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arrangement — but it means a whole family is judged on four blocks instead of
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five. If your scene fills the frame corner to corner, expect to earn your score
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on `orient` and `texture`.
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---
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## What has actually worked
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Ordered by measured effect.
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### 1. Draw the song's content instead of your own
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The largest single lever. Take `consumes: ['cast', 'ink', 'staging']` and draw
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`castMain`/`castChorus` where you would have drawn your own primitive. Recipe in
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`MIGRATION.md`.
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Measured: identity is worth 117% of what the container is worth
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(`checks.html?decompose=1`) — swapping the song's cast under a fixed scene moves
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the picture more than swapping the scene under a fixed cast. A migrated library
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scene also carries the identity better than a stage written from scratch to
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carry it, which was a surprise and is why the whole library was migrated rather
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than replaced.
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### 2. Let the song decide element SIZE
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`stageScale()`. Not the size of your features relative to each other — the size
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of the whole vocabulary. A song of six huge forms and a song of four hundred
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tiny ones are different videos before anything else is decided.
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Measured: adding `elementScale` to the identity moved stages from
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+0.0111 ±0.0043 to +0.0143 ±0.0008, and the `scale` block from 0.033 to 0.041.
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### 3. Displace a regular lattice
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If your scene is a grid, let the song push things off it. Bounded — past about
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half a cell the structure the grid was providing stops reading.
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Measured: Isometric Blocks 0.034 → 0.049, with `orient` nearly doubling from
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0.093 to 0.164 as the rigid lattice softened.
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### 4. Give a full-frame field somewhere to be about
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`focusWarp(p, amount)` and `focusField(p)`. The song picks one to three focal
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points; tile in the warped coordinate so cells crowd toward them or pull away.
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Measured: Voronoi Shatter 0.0463 → 0.0588. **Note what moved:** `orient` 0.140 →
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0.194, while `layout` went 0.004 → 0.007, i.e. nowhere. Warping where cells sit
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changes what they look like without changing where the frame's energy is. The
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gain is real; the stated reason for it was wrong.
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---
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## What has measurably NOT worked
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Recorded because the failures were more informative than the wins, and because
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each of these looked obviously right beforehand.
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### Effects as parameters
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Forty-nine scenes had their own `glow`; every one had its own grain. An effect
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knob sampled per song makes a scene look varied across parameter draws while its
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structure never moves — it inflates the score without changing the picture, and
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it fights the grade, which already does bloom, grain, chroma and vignette with
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an envelope the scene cannot see.
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**Do not add glow, bloom, grain, haze, chroma or trails to a scene.** The post
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chain owns them. `npm run lint:scenes` does not catch this yet; reviewers should.
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### Concentrating disturbance instead of adding it
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Isometric Blocks, twice. Spending the scatter budget near the focal points and
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calming the rest measured 0.049 → 0.0374 — most of the field went back onto the
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rigid lattice and took the orientation variety with it. Making the focus
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additive instead recovered nothing: 0.0365.
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Two plausible diagnoses, both wrong. The lesson is narrow and worth keeping:
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**a focal point has to be something the field gains, not something the rest of it
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pays for** — and even that framing did not rescue it, so the real cause is still
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unknown.
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### Making the roster smaller
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A whole afternoon went into the theory that a track drawing on fewer scenes
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would look more like itself. Swept directly across pool sizes 4, 8, 16 and 32
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over twelve songs with three draws each: differences of 0.003 to 0.007 against a
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run-to-run noise of ±0.003 to ±0.005. **Nothing.** The theory came from an
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experiment whose arms differed in two ways at once.
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### Reading a form as a metric rather than drawing it
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Spectrum Sculpture used `sigShape` as a radial distance rather than as a subject.
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Migrating it to `castMain` rendered pure black, because the cast carries notches
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and a hollow and an annulus used as a radius turns a sculpture inside out. If
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your scene consults a form's geometry rather than drawing it, it wants
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`sigShape`, and the cast is not for you.
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---
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## Scene shapes, and how hard each is to vary
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- **Element-placing** (`metaballs`, `floating-geometry`, `firefly-drift`) —
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easiest. Take the cast, place on `stageNode`, keep your motion. Nearly all the
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wins above are this shape.
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- **Single figure** (`slow-orb`, `eclipse-field`) — take the cast and
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`stageScale()`. Composition is yours to vary; most such scenes centre their
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subject and never move it, which is free `layout` left on the table.
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- **Full-frame field** (`voronoi-shatter`, `plasma-bloom`, `curl-flow`) — hard.
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`layout` is unavailable to you. Earn it on `orient` and `texture`, and consider
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a focus.
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- **Fixed geometry** (`truchet-fold`, `quasicrystal`, `apollonian-gasket`) —
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hardest, and currently unsolved. The image *is* the maths, so the cast cannot
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be pasted on top of it. The open idea is to make the cast the repeating UNIT
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the tiling is built from, which is a real rewrite per scene rather than a
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recipe step. Nobody has tried it yet.
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- **Treatment** (`analog-wow`, `scan-tear`, `halftone-misprint`) — these are
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effects wearing a scene's clothes. They score 0.031–0.040 and their whole
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migration was one posterisation. They probably belong in the identity's
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effects register rather than competing for screen time as subjects.
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---
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## Trusting the numbers
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This harness has two classes of measurement and only one is safe to steer by.
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**Direct render comparisons** — the gallery score, `checks.html?decompose=1`, the
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per-scene gate — compare rendered frames to each other. Noise floor of exactly
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zero. Trust these.
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**Aggregate ratios** — chiefly `separation`, which divides one small difference
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by another — swing wildly. Three runs of the same post-migration measurement gave
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0.31, 0.56 and 0.07. **Four conclusions were drawn and withdrawn during this epic
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for exactly that reason.** Anything under about 0.01 of spread needs
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`&repeats=3` before it is believed, and a difference that changes sign with the
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sample size is not a difference.
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Two more traps, both of which have bitten:
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- **A score of exactly 0.000 is a dead shader, not a boring scene.** The gallery
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now says so outright — the row goes purple and carries the luminance and
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variance — but the underlying trap is general: a broken render produces the
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most boring possible numbers rather than an error.
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- **A permanently-zero block looks like a property of your scene.** The gallery
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built four of the descriptor's five blocks for weeks; `motion` came back 0.000
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for every scene and depressed every score by a fifth. If a block is identical
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across many unrelated scenes, suspect the instrument.
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- **Arms that differ in more than one way cannot be read as if they differed in
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one.** This produced the roster-size result above, and it was believed for a
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day.
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---
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## Checklist for a new or reworked scene
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1. `consumes` declared, and the `consumes:` lines pass in
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`checks.html?scene=<name>`. A declared artifact that is ignored is worse than
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one not declared, because the casting code believes it.
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2. No glow, bloom, grain, haze, chroma or trail parameters.
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3. Element size goes through `stageScale()`.
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4. Placement goes through `stageNode()` unless the composition IS the scene.
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5. Gallery score above 0.04, checked before and after.
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6. The rest of the per-scene battery still passes — especially `distinct`. The
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more scenes share a cast, the easier it is to become one of your neighbours.
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---
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## Open questions
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- **Coupling is zero and has never moved.** Whether a song *looks* different in
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proportion to how it *sounds* different measures -0.02 ±0.03. Every change in
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this epic left it there. Nobody has attacked it directly.
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- **Fixed-geometry scenes** have no known route to variety.
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- **The `layout` blindness** for full-frame fields would need a new descriptor
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block measuring cell statistics rather than where structure sits.
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- **The 0.04 bar** is a starting point, set where the flat cluster sat — and set
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against scores that were depressed by the motion bug. It deserves re-deriving.
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