The uinput gamepad backend emitted only XOR-changed button edges while
advancing `prev_buttons` unconditionally. Because `emit()` is best-effort
(a full kernel queue silently drops the write), a dropped EV_KEY edge was
never re-synced — the button stayed stuck (pressed-not-released, or vice
versa) until it next toggled. The axes never had this problem: they
re-emit their absolute value every frame.
Re-assert every mapped button's absolute state each frame, exactly like
the axes, and drop the now-unused `prev_buttons` field. Restating an
unchanged key is free downstream: the kernel input core discards an
EV_KEY whose value already matches the device's current state (no
duplicate event reaches consumers, and BTN_* keys don't autorepeat). The
`emit()` "next frame re-syncs state" comment is now honest for buttons
too.
Verified on the Linux host build (.21): cargo clippy -D warnings clean
(no dead-field warning), full punktfunk-host suite 277 passed / 0 failed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
0c427cb3f1