The 240Hz monitor delivery + one-in-flight conversions + naive double-per-pixel
DownscaleBgra (~150ms/frame under load) froze the desktop layer 90% of take
ty-1742 (6.1 fresh content updates/s, freeze runs to 2.8s; decoded raw-frame
audit). The render stat (33-36ms) was real but moot — the capture CONVERSION was
the wall, and the one torn frame was a ring slot rewritten under the consumer's
read. Reference: WGC delivers at DWM/monitor cadence
(https://learn.microsoft.com/en-us/windows/apps/develop/media-authoring-processing/screen-capture)
and libyuv row-simple/fixed-point scaling
(https://chromium.googlesource.com/libyuv/libyuv/) — the repo's own take-4 rule.
- DownscaleBgra: integer 8.8 fixed-point, shift-only-at-the-end (same two-stage
math as SceneCompositor.Bilinear). ~150ms -> ~5ms per 2.5K->1080p frame.
- 10ms MinConvertInterval: the ~4.2ms 240Hz tail stopped queuing ~150ms of
serialized conversion/s; capacity sits just above the 60/s the pump can use.
- FrameRingBuffer (depth 8, redLine 4): reuse-DISTANCE ring — a buffer is only
rewritten >=4 rents after its last hand-out else fresh-allocated, so a frame a
consumer still holds (session.LatestFrame survives conversions, dispatcher
preview lags) is never read-while-overwritten. Needs no consumer Release API.
- 2s startup.log telemetry: frames/s, conv avg/max ms, skip busy/cadence, ring
allocs — the device take is judgeable numerically.
Good Dog test: Ring_NoLap_ReusesOnlyAfterRedLineRents. 295/295 green, 0 warnings.
C4 (composite Epoch-cached downscale) deferred pending the device re-measure.
Local only, no push.
Roll-forward of today-slices 6fd1d9c onto the slice-8 base, two-loop hunk dropped.
Release counter (per-build GUID read as noise; +1 per commit from git rev-list,
baseline 241 -> #13, generated by GenerateBuildStamp; GUID demotes to startup.log).
Tests pinned to Label/#N >= 13; wordmark display test asserts the Label.
Flash fix (take 14 finding): consumer holds must never outlive depth x source
period — 4 slots at high refresh lap ~27ms vs a <=50ms compositor read, so a
recycled slot flashed its new frame over the lagged old one. All shared rings 4->8
(OBS/overlay precedent for ring discipline).
Camera producer now rotates an 8-deep ring + Epoch instead of a fresh ~3.7MB
array per device frame (110-220MB/s LOH churn); WebView2 capture reuses a canvas
scratch + 8-deep output ring + a reused WriteableBitmap instead of two fresh
arrays + a fresh bitmap per 10Hz tick. Paste cache stays identity-keyed (Epoch).
Take 11 (c10ce06c) validated the off-UI architecture: typical frames land
work ~10ms + wait ~6.8ms = 16.7 exactly on the deadline; 212/300 best yet.
The ENTIRE remaining gap is periodic 35-65ms render spikes that WORSENED
across the take (189 -> 147) — the signature of gen2 GC pauses. Biggest
churner is structural: the screen capture minted a fresh ~8.3MB byte[] per
DWM frame (~500MB/s of LOH), a producer OBS never does (it owns fixed
surface pools).
- ScreenCaptureFrameSource: 4-deep buffer ring with size-matched slots (a
<=17ms consumer cannot be lapped at 60Hz) + reused downscale row scratch.
- VideoFrame.Epoch: monotonic per producer frame. The paste cache keys on
array IDENTITY, so recycled arrays MUST be distinguished — epoch joins the
PasteKey. Producers handing fresh arrays leave it 0 (key unchanged effect).
- Stats print 'gen2 +N' per 5s window: next take acquits or convicts GC
without another guess (rule: prove the stage).
- Test (the ONE): PasteCache_RecycledArrayWithNewEpoch_ReRasterizes_NotStaleHits
— same array, new content, bumped epoch; fails on the old key by
construction. 37/37 compositor/pump, clean build.
- Next suspect if gen2 stays hot: the 10Hz WebView2 capture (full-canvas PNG
decode + fresh arrays on the UI thread) — recorded, untouched.
Creator audio ask queued in the same working session (+40% post-mix master
gain before the -1dBFS limiter) lands as its own commit next.
gramps