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miga-heygenandMiguel Ángel 9aa60a844f fix(registry): make motion-blur match After Effects shutter-based blur (#4008)
* fix(registry): make motion-blur match After Effects shutter-based blur

The motion-blur catalog snippet estimated speed from the x/y delta
between consecutive timeline updates and drew three one-sided ghost
copies with decaying alpha plus a Gaussian on top. After Effects does
temporal supersampling: each frame integrates the layer over a shutter
window (shutter angle, shutter phase, samples per frame), producing a
symmetric box smear of length speed x shutter time.

The snippet now does the same inside the page. After every timeline
update a deferred pass seeks the GSAP timeline to N sub-frame times
across the shutter window (events suppressed), reads each target's x/y,
restores the frame time, and drives an SVG filter that averages N
feOffset copies with equal weight (feComposite arithmetic, 1/N, sRGB).
Defaults follow AE: shutterAngle 180, shutterPhase -90, samplesPerFrame
16; fps comes from the render config, then the root data-fps, then 30.
Displacements are mapped through the inverse of the element's own
scale/rotation; percent x/y values are resolved to px; SVG targets use
their bbox; an existing inline filter is kept and the blur appended to
it. The pass runs in a microtask rather than inside the tracker tween's
onUpdate, because seeking GSAP from within its own render reads stale
tween state and suppresses the composition's callbacks on forward
seeks. The heuristic options blurScale/blurMax/stretchScale/stretchMax
are removed.

Reference: an AE-algorithm reconstruction of the same composition
rendered without the component at an effective 960 fps and averaged
over the 16 sub-frames of the 180 degree window per output frame.
Against it (1920x1080, 30 fps, solid + text translating linear then
power2.inOut): old mean PSNR 53.2 dB (min 26.7), SSIM 0.9930; new mean
PSNR 72.4 dB (min 52.6), SSIM 0.9998. The 10-90 edge ramp at 66.7
px/frame is 26.8 px in the reference, 27.5 px new, 14.5/6.3 px
(one-sided) old; at the ease peak 79.3 vs 79.5 vs 7.9/17.7 px, with
smear centres matching to 0.1 px.

Co-Authored-By: Miguel Ángel <miguel.sierra@heygen.com>

* fix(registry): drop render-config fps probe from motion-blur and refresh its docs

The snippet resolved fps by reconstructing the renderer's private seek
config key so the compiler's inline-script guard would not strip it. A
public catalog snippet must not depend on that key, so fps is now the
explicit option, then the root data-fps, then 30; renders with an fps
override pass fps explicitly. The catalog page's Usage, How it works and
Options sections still described the old velocity heuristic and are
rewritten for the shutter model. The 1/N weight keeps full precision.

Co-Authored-By: Miguel Ángel <miguel.sierra@heygen.com>

* fix(registry): match the After Effects reference export's shutter window

The shutter model landed on this branch was built against a reconstruction
of After Effects' algorithm, not against After Effects. A real 1920x1080 /
30 fps export of translating text disagrees with it on three points, all
measurable off the export itself.

The window is two frames wide, not half a frame. On the measured frame the
outermost duplicate on the trailing side sits 128 px back while the previous
frame is 125.8 px back, and the outermost leading duplicate sits 189 px ahead
while the next frame is 184.9 px ahead: the window ends land on the
neighbouring frames. Defaults become shutterAngle 720, shutterPhase -360.

Duplicates sit on the sub-interval boundaries, both ends included, not at
sub-interval centres. The staircase across a stroke steps every 15.6 px on a
125.8 px displacement and every 23.0 px on a 184.9 px one, i.e. an eighth of
a frame, with the run closing exactly on the neighbouring frame's position.
samplesPerFrame now means sub-intervals of the window, so there are N+1
copies at k/N rather than N copies at (k+0.5)/N.

The frame-time instance is drawn sharp over the smear. At full ink the core
bounding box is the whole word at every frame and total ink rises to 1.44x
the unblurred frame's, neither of which an average can produce. A final
feComposite over of SourceGraphic reproduces it. Each duplicate stays at
1/N: the staircase plateaus step by 0.063 +- 0.002 of the sharp text
intensity, flat, with no taper toward the window edges, and triangle
weighting scores 1.6 dB worse against the export.

Verified by replaying the export's translating section as a composition
whose sprite is the export's own rest-frame ink and whose eight legs follow
its own measured per-frame positions, rendered at 1920x1080 / 30 fps and
compared frame by frame over the text band. Mean PSNR against the export
rises from 24.19 dB (min 17.07) to 32.51 dB (min 27.57) across 72 frames,
and from 19.83 dB (min 17.07) to 32.03 dB (min 27.57) across the 26 frames
that actually move. Ghost extents match to a few px and the rendered
staircase plateaus match the export's to two decimal places. The export's
later scale, skew, flip and 3D rotation sections are out of reach here:
integrating anything but translation inside the shutter is engine work
tracked in issue #4010.

The filter region now clamps its bounds through zero. It was derived from
the duplicate offsets alone, which was correct while the output was nothing
but duplicates; the sharp instance draws at offset zero, so a window sitting
entirely on one side of the frame time - any shutterPhase above 0 or below
-shutterAngle - produced a region starting inside the element's own box and
cut the instance off. The defaults straddle the frame time and were never
affected, so the measured numbers above are unchanged.

Co-Authored-By: Miguel Ángel <miguel.sierra@heygen.com>

---------

Co-authored-by: Miguel Ángel <miguel.sierra@heygen.com>
2026-09-17 00:51:03 +00:00
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