motion-quality
Installation
SKILL.md
Motion quality
Every rule here was paid for. Each one is a bug that shipped, was measured on rendered frames, and cost a user their afternoon. The numbers are real — they are in the file so you cannot talk yourself out of the rule.
Rule 0 — you cannot see a sub-pixel bug. Measure the frames.
"It looks fine" is not a claim about a frame-accurate animation. Render the frames and measure them. Four checks catch almost everything:
| what | why it works | what a failure looks like |
|---|---|---|
| Consecutive frames where nothing is animating must be byte-identical | the style is unchanged, so the pixels must be | non-zero diff = the renderer is non-deterministic |
| Under a monotone scale, the ink's vertical centroid must move monotonically | it is a pure affine map | direction reversals = the type is snapping to the pixel grid |
ink area / width² cannot change under a scale |
it is a shape invariant of a rigid shape | drift = the glyph outlines are changing shape (hinting) |
| No frame should move < 0.5px while it is supposed to be animating | sub-pixel motion rasterises to an identical frame | a run of them = the animation is visibly frozen |