Rewind was on for everyone and could only be turned off with PSX_REWIND=0 in
the environment. It now defaults off and is enabled from settings.toml
([video] rewind) or the launcher's Display card.
The cost it was charging silently: each snapshot is a whole machine — 2 MB main
RAM + 1 MB VRAM + 512 KB SPU RAM — serialized uncompressed into a buffer
malloc'd at a fixed 5 MiB cap that is never shrunk to the actual length, and one
is captured every rewind_interval frames (15 by default, tightening toward 4
while an FMV runs), each with a 128x96 thumbnail built pixel by pixel. At the
default depth of 50 a full ring is roughly 250 MB resident; at the maximum 200
it approaches 1 GB. That is a lot to hand a low-end host for a feature a session
may never open.
Turning it off genuinely avoids all of it: psx_rewind_configure() returns before
any allocation when rewind is not wanted, and both capture paths are guarded by
psx_rewind_enabled(). The only residue is a 450 KB BSS overlay panel whose pages
stay untouched.
The toggle applies live rather than at next launch — freeing the ring is the
whole point, so waiting for a restart would miss it. psx_rewind_shutdown()
already resets the overlay and drops a pending load, so tearing down mid-session
is safe.
PSX_REWIND still outranks the setting in both directions and now accepts 1 as
well as 0. Netplay rollback is a separate subsystem with its own ring and is
unaffected; rewind was already suppressed during netplay.
Because off is now the common case, psx_rewind_toggle() says so on the OSD
instead of leaving F8 / Select+R3 looking broken. It stays silent only in a
-DPSX_REWIND=OFF build, where there is nothing to enable.
Adds rewind_settings_test (default off, explicit off distinguishable from
absent, save/load round trip, tuning keys independent of the enable) and the
first documentation the feature has had, in config_schema.md.
Verified: recompiler tests build and pass; main.cpp type-checks against the new
recomp-ui ABI field; psx_rewind.c compiles both with and without
PSX_HAS_RBENGINE_SNAP; the existing test_rewind_toggle_combo.py still passes.
Not run end to end — this checkout has no BIOS dump to boot.
Needs recomp-ui a31ecbc for Settings.rewind_enabled.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017AwqKPQFnK3x7xQbK4PQKj
Alex Vanderveen
77095c589c