WP3 of design/desktop-presentation-rebuild.md. The `vsync` and `allow_vrr`
settings have existed since WP1 but nothing consumed them — the swapchain picked
MAILBOX-or-FIFO once, from an env var, and froze. This makes them mean
something, which is also what unblocks their settings rows (deliberately
withheld from WP5 rather than shipped as dead switches).
Present-mode selection is now a preference ladder, not a constant:
* V-Sync off — IMMEDIATE, then FIFO_RELAXED, then the tear-free modes. Asking
to tear and silently getting vsync is a lie, so the mode that actually took is
named in the stats line and a refused preference is logged requested-vs-active.
* V-Sync on + VRR allowed + fullscreen — FIFO first. On a variable-refresh panel
with direct scanout the FIFO present IS the flip, so the panel follows the
stream's cadence instead of a fixed grid; MAILBOX would decouple presents from
scanout and re-quantize to the compositor's clock. This is only safe because
WP2's glass gate bounds the standing queue that historically made FIFO costly.
* Otherwise — MAILBOX then FIFO, the shipped default, unchanged.
`PUNKTFUNK_PRESENT_MODE` still pins a mode outright and now falls back to the
settings (rather than to mailbox) when the name is unknown.
VRR detection is MEASURED, never queried. No portable query exists — SDL exposes
none, Wayland does not report adaptive-sync state, Windows surfaces nothing
through Vulkan — and the platforms that do answer have been caught lying (see
the Android per-uid refresh-rate finding). The discriminator is quantization: on
a fixed-refresh panel every on-glass instant lands on the vblank grid, so the
spacing between presents is ~k×period for whole k even when the stream runs
slower than the panel (it just picks a larger k); under real VRR the panel
refreshes when we present, so the spacing follows our own cadence and sits off
the grid. `CadenceProbe` folds each delta to its distance from the nearest
multiple of the learned period and takes the median. Tri-state: it stays Unknown
below 24 deltas and after a display change, so `vrr` is reported only when it
has been measured — never inferred from what the display claims.
Also fixes the read-once refresh rate: `native.refresh_hz` was sampled at
startup and never revisited, so dragging the window to another monitor left a
60 Hz-seeded clock pacing a 144 Hz panel. `WindowEvent::DisplayChanged` now
relearns the latch grid, resets the cadence verdict, and clears the served-slot
latch.
Settings rows for both, on all three surfaces (GTK, WinUI, console). The
console's V-Sync row is reachable in Gaming Mode, which is the only editor a
Deck user has.
Gates: punktfunk-rust-ci linux/amd64 — fmt, clippy -D warnings over
pf-client-core, pf-presenter, pf-console-ui, the session binary and the GTK
client, 160 tests (the two new ones cover every ladder and both cadence
regimes, including the case that matters most: a stream slower than a FIXED
panel must still read as fixed). WinUI leg on the Windows runner .133:
clippy=0 tests=0, against a tree proven by content to contain the edit.
⚠ On-glass validation is still owed and is NOT claimed here: every box with a
real display was powered off when this landed, so the VRR ladder and the
detector have been exercised only against synthetic stamps in unit tests.
Rebase follow-up: `20de58a7` landed the same "panel grid can be wrong in both
directions" defect fix on Android and extracted the corrected learner into
`punktfunk_core::phase::PanelGrid` for the iOS and desktop presenters to share.
This clock had the identical bug — it capped the learned period at the display
mode's refresh, and the mode is only a CLAIM, so a display really running slower
than it advertises pinned a grid whose instants never arrive, for the session,
with no way back. Adopted the shared learner rather than carrying a second,
buggier copy; still fed the window's MIN spacing, which preserves the k×period
resistance the cap was actually aimed at while the streak requirement lets a
genuinely slower panel be discovered. New test: seed 120 Hz, real panel 60 Hz,
the clock must climb back out.
Took the same commit's third lesson too: the adaptive margin widened on a
latch over 1.5×period (a number picked here), and now widens on the latch
exceeding one period plus the lead already applied — the slot actually aimed at.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
enricobuehlerandClaude Opus 5
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