sylph-decoder d694bcc53f re: the sweep ramp is DECODED -- four leaf keyframes, and the GPU agrees on sign and magnitude ...

The port asked for the sweep strips' vertex alpha as a function of position. It
is not a runtime curve to sample: ptloop01/ptloop02's nested leaves declare four
keyframes each, with x, alpha, rotation, scale and time.

  pteff03   loop 600u  x -639 -> 1521, alpha 255 -> 128 -> 255, rot +30, sy 600 %
  pteff03a  loop 720u  x 1721 -> -839, alpha   0 -> 128 -> 255, rot -45, sy 800 %

Checked against three sessions of GPU draws: both signs right every time, and
magnitudes within ~15 % of the declared slopes.

The independent bit worth having: across sessions the measured alpha spans
45..242, and only pteff03a declares alpha below 128 -- pteff03's ramp never
leaves [128,255]. The strip measured at 45 is the 1303-tall one, which the AABB
geometry says is pteff03a for a completely different reason. Two identifications
agreeing.

Stated as limits rather than buried: this cannot separate the two declared
slopes, which are 25 % apart against a quantisation of 6.4 px and one alpha
level over 3-4 frames; and absolute phase is unchecked because the AABB-left to
element-x mapping under rotation and pivot is not established.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wuu56cE8vJGTBtn1ppsk8v

2026-08-31 07:11:09 +00:00

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