enricobuehler 0170da2a5f fix(client/apple): stop dropping rotation, and stop inventing it ...

G13 — the three capture-fidelity findings from the gyro sweep, two fixed and one
argued.

**The 4 ms floor was a DROP, and it was shedding real rotation.** A sample arriving
3.9 ms after the last one was discarded outright. That is the wrong shape for this
signal: buttons and sticks are absolute state, so a dropped frame costs nothing — the
next one says everything it would have. Angular velocity is a RATE, and a consumer
integrates it into an angle, so a dropped sample is rotation that happened and can never
be recovered. GameController's delivery jitters around the pad's own ~250 Hz, so a floor
set AT that rate does not shed a rare extra sample; it sheds a steady fraction of every
turn. And the error is one-signed, so it accumulates — aim drifting short, which reads
as bad sensitivity rather than as a bug.

Nothing needed the ceiling. GC delivers at the sensor's rate rather than faster, the SDL
client has always forwarded every sample, and the host's idle watchdog is a 100 ms
timeout this cannot outpace. The throttle's two fields went with it: `lastMotionNs` was
left set-but-never-read once the guard was gone, and `motionIntervalNs` had no other
consumer. (Notes elsewhere say `flush` parks motion and reads it — that is PR #88's
branch, not this one. Checked rather than assumed.)

**An X-Box pad was streaming gyro it does not have.** Capture attached to any `GCMotion`,
and an X-Box controller exposes one that reports gravity and NOTHING else. So the client
sent a permanently-zero `rotationRate` to the host as authoritative gyro, under a
declaration saying this pad has one. That is worse than having no motion plane at all: a
game sees a controller being held perfectly still forever, and there is nothing to fall
back to and nothing to notice. Now gated on `hasRotationRate`, which is GameController's
own answer to the question we actually mean.

The settings badge had the same bug from the same cause — `hasMotion` was
`motion != nil`, so an X-Box pad got a gyroscope icon. It now reads `hasRotationRate`
too. One wrong predicate was driving both the UI promise and the wire behaviour, which is
why they were wrong together.

That also simplifies G8's "your gyro can't reach this session" notice, which had to test
`hasRotationRate` itself to avoid nagging about a gyro the pad never had. With the attach
gated on it, the notice is just the else-branch.

**Motion stays on the main queue, and this is the argument for why.** GameController's
`handlerQueue` is a property of the CONTROLLER, not of an element, so moving motion off
main moves buttons, sticks, the touchpad and the escape chord with it. This class is
`@MainActor` throughout — eight `assumeIsolated` sites, the slot table, the gesture
timers — so that is a rewrite of the isolation model rather than a queue assignment, and
it would put the tvOS escape chord (the only controller way out of a stream there) on a
background queue. That is a real risk for a speculative gain. The comment says so at the
call site, and names the measurement to make first if it ever does bite: the host's
per-pad motion inter-arrival histogram already reports exactly this and would say whether
the delay is client-side or on the wire.

Gate: macOS `swift build` + the full suite (215 tests, 5 skipped, 0 failures) and the
iOS-triple typecheck green. No test pins the throttle removal or the capability gate:
both are properties of live `GCMotion` delivery, which this module cannot fake — there is
no injectable seam, and inventing one to assert "we called sendMotion twice" would test
the mock. They are argued at the call sites instead, in the same spirit as the parts of
`DsCapture` that are not unit-testable in their module either. On-glass verification is
owed with the two already outstanding on that rig.

2026-08-07 19:12:02 +02:00

..

punktfunk_core.h

fix(client/apple): stop dropping rotation, and stop inventing it

2026-08-07 19:12:02 +02:00