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Brows: traced ring, quantised raise

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A brow at 320x200 is fourteen pixels wide and three tall. Its shape carries
almost nothing at that size; its height above the eye carries the expression,
and a brow raise is the most legible beat on a face. So the ring is traced and
the height is quantised - the split the eyes already got, where the lid is a
traced feature and the iris a quantised primitive.

The decomposition is the point. The traced ring already contains the real
height, so adding a quantised raise on top would move the brow twice. The
height is measured OUT of the ring, quantised, and put back, so the shape that
renders is his at a height that snaps between a few levels and holds.

Measured at both ends rather than as one number, because raise and tilt are
different expressions out of one mechanism: both ends up is surprise, inner up
alone is worry, inner down is anger. They share a dwell - the gaze quantiser,
renamed quantizeSnap now that it has two callers - so the brow hits its pose in
one frame instead of crawling into it with one end arriving before the other.

Measured against the eye's corner midpoint, never its lid. Same trap the gaze
origin has and worth avoiding twice: brows and lids move together constantly,
so a brow that jumped on every blink would read as a tic. Rest pose from the
take median rather than the neutral frame, for the reason gaze learned the hard
way - that frame is picked by minimum mouth aperture and says nothing about the
brows.

Two correspondences resolved from geometry, not declared: which ring is which
brow, and which end is the outer one. The second matters more - backwards, the
tilt mirrors and worry renders as its own opposite, which reads as a directed
performance choice rather than a bug and would never be questioned. Which EDGE
is upper is deliberately left unresolved: it traverses the same ring the other
way, an even-odd fill has no winding, and both ends still land on fixed slots.

Also fixes a bug from the exposure work: the live render applied exposure to
the plate and the mouth but not to the eyes, so on 2s the preview and the
export disagreed. A preview that disagrees with the export is the one bug this
tool cannot afford. perfIndex now exists as a named thing so the two paths
cannot drift apart again.

91 -> 105 assertions. Ground truth on all four synthetic brow poses, tilt
separating worry from anger by sign, a blink not faking a raise, and a shared
dwell never emitting a half-raised brow.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Your Name 2026-09-24 18:11:25 -04:00
parent 2e4406d579
commit 03df81fa0b
8 changed files with 419 additions and 26 deletions
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45
README.md
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@ -201,6 +201,47 @@ other way round to prove it actually looks.
| iris size | Diameter as a percentage of eye width. |
| pupil | Square pupil in whole pixels. 0 = off. |
## Brows
A brow at 320×200 is about fourteen pixels wide and three tall. Its **shape**
carries almost nothing at that size; its **height above the eye** carries the
expression, and a brow raise is the most legible beat on a face. So the ring is
traced and the height is quantised — the same split the eyes got, where the lid
is a traced feature and the iris a quantised primitive.
The decomposition matters. The traced ring already contains the real height, so
adding a quantised raise on top would move the brow twice. Instead the height is
measured *out* of the ring, quantised, and put back: the shape that renders is
his, at a height that snaps between a few levels and holds.
Height is measured at **both ends**, not as one number, because raise and tilt
are different expressions out of one mechanism — both ends up is surprise, inner
up alone is worry, inner down is anger. They share a dwell, so the brow hits its
pose in one frame instead of crawling into it with one end arriving first.
It is measured against the eye's **corner midpoint**, never its lid — the same
trap the gaze origin has, and worth avoiding twice: brows and lids move together
constantly, so a brow that jumped on every blink would read as a tic. The rest
pose comes from the take **median**, not the neutral frame, for the same reason
gaze does: that frame is chosen by minimum mouth aperture and says nothing
whatever about the brows.
Two correspondences are resolved from geometry rather than declared: which ring
is which brow, and which end of a ring is the outer one. The second matters more
— get it backwards and the tilt mirrors, so worry renders as its own opposite,
which reads as a directed performance choice and would never be questioned.
Which *edge* of the brow is the upper one is deliberately left unresolved: it
traverses the same ring the other way round, an even-odd fill has no winding,
and the two ends still land on fixed slots either way.
| Knob | What it does |
| --- | --- |
| brow vertices | Ring vertex budget, off a 10-slot ring. |
| brow weight | Thickens the ring outward. It needs it at three pixels tall. |
| brow raise gain | Exaggerates or damps the raise. |
| brow step | The pixel grid the height snaps to. 0 = off. |
| brow dwell | How long a new height must hold. Shared across both ends. |
## The plate is reference, not art
The plate layer has several representations because its job changes. Cycle with
@ -268,7 +309,7 @@ chromium --headless --virtual-time-budget=8000 --dump-dom \
http://127.0.0.1:8777/selftest.html | grep -oE '(PASS|FAIL) [0-9/]+'
```
Or open `selftest.html`. 88 assertions over the stages below detection, plus a
Or open `selftest.html`. 105 assertions over the stages below detection, plus a
wiring cross-check: every `el('id')` in `app.js` must exist in `index.html`. A
knob wired in one but not the other throws during wiring, which aborts the rest
of the module and leaves a blank page — a symptom that points nowhere near its
@ -282,7 +323,7 @@ eyeball.
## Not done yet
Brows; hand-drawn head plates and per-plate mouth slots (the strip
Hand-drawn head plates and per-plate mouth slots (the strip
decides *which frames need one*, but you cannot yet supply the drawing); real
performer→character calibration (currently identity, fitting the face oval to the
canvas); the override layer; anything on the Animator Pro side. The plate is a