Root cause of scroll jank: first-present of each Image uploaded pixels
inside the render frame (~11-30 ms per 400px texture, 1.3 visible
hitches/s at 120 Hz; grey-image A/B: 20 -> 1). Slint has no render
thread and no pre-upload API.
Fix: decode worker creates the Rgba8Unorm texture on Slint's own wgpu
device (captured from GraphicsAPI::WGPU30 at RenderingSetup) and submits
the async upload; UI wraps it in Image::try_from(tex). Zero pixel work
in the render frame. CPU from_rgba8 fallback retained.
Measured (Pixel 9 Pro 120 Hz, 400 px, per-frame FR hook):
before: >10ms renders 20 in 15s (max 30 ms), 3 borderline 8-9 ms
after: 0 mid-scroll renders > 4.4 ms (median 1.9, p95 2.9);
only post-idle first-frames expensive (invisible)
Also: FR per-frame logging via set_rendering_notifier; APLY timestamp.
Slint's android-activity backend wakes the main loop from a dedicated
"slint vsync" Choreographer thread while any animation is active
(i-slint-backend-android-activity/vsync.rs). Android schedules that
thread at nice +10 (lowest on device), while our 4 turbojpeg workers
inherited the UI thread's nice -10. Under CPU bursts the +10 waker
starves and the main loop's next wakeup lands 3-4 frames late: 25-33 ms
of pure wake latency at 120 Hz, with zero cost in our tick (d=7-34 us) —
exactly the phone stall signature (measured: 28-39 ms gaps, catch-up
events).
- prio module: setpriority FFI (self + by-tid), raise_slint_vsync()
- thumb workers + dispatcher: nice +2 at spawn (ahead of background
apps, behind the UI's -10)
- android_main: prio-fix thread raises "slint vsync" to nice 0 with a
readback log
- verified on emulator: thumb-* hold nice 2, slint vsync holds 0 while
foreground (Android re-nices backgrounded processes — expected)
- emulator scroll cadence unchanged (llvmpipe rasterization ceiling,
not a priority issue) — phone is the acceptance target, A/B test
planned for when it is back online
Also: drop unused android_logger dependency (nblog replaced it).
- scan.rs: recursive walk of Pictures/DCIM (GALLERY_SCAN_DIRS override),
image-ext detection, mtime/size capture, no symlink-dir following
- db.rs: rusqlite(bundled) store; incremental apply (insert/update/delete)
keyed on path with mtime/size change detection; derived columns reset on
change; Android DB path in Android/data/<pkg>/files (EXTERNAL_DATA_DIR is
unset in this NativeActivity setup)
- lib.rs: start_scan() background thread -> invoke_from_event_loop ->
VecModel + status line; called from desktop and Android entry points
- main.slint: ListView of paths (M1), status line with scan stats
- main.rs: fix desktop bin for 1.18.1 (no slint::Result; ComponentHandle)
- build.sh: export NDK clang CC_/CXX_/AR_ per target (bundled sqlite)
- tests: 5k-file scan < 2s, incremental apply, roundtrip
Verified on emulator: 5002 files in 153-226 ms; relaunch 0+ 0~ 0-;
touch -> 1~, delete -> 1-.
