feat(#16): optional exposure/framerate lock#19
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Auto-exposure raises frame time past the 33ms budget in low light, halving fps to ~15. Add an optional control to pin the camera to Manual exposure so framerate holds steady, at the cost of a darker image. Off by default. Native: worker queries IAMCameraControl off the reader's media source; when the camera supports Manual exposure it maps a normalized 0..1 value onto the camera range (snapped to stepping) and pushes on change; OFF restores Auto. No-ops when unsupported; restores Auto on shutdown. ABI: CosParams += exposure_lock_enabled + exposure_value; CosStatus += exposure_supported (support is per open camera, known only while running, so surfaced via the polled status not the pre-start capability probe). C#: ShimParams/ShimStatus + PInvoke mirrors; EffectSettings persistence; VM observable ExposureLock/ExposureValue/ExposureSupported with live push + config round-trip; XAML toggle + brightness slider, greyed until running and supported. The native camControl==null check is the authoritative gate (not a managed ApplyParams gate, which would force exposure off at Start before the first status poll and break persisted-on exposure). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Closes #16.
Problem
Webcam auto-exposure raises frame time past the 33 ms/frame budget in low light, so the camera physically drops to ~15 fps. Confirmed live (overlay reads ~15 dim, 30 bright). Camera firmware behavior, not the capture pipeline.
Change
Optional control to pin the camera to Manual exposure so framerate holds at 30 regardless of lighting, at the cost of a darker image in dim rooms. Off by default (keeps auto-exposure).
IAMCameraControloff the reader''s media source; if the camera supports Manual exposure it maps a normalized 0..1 value onto the camera range (snapped to stepping) and pushes on change; OFF restores Auto. No-ops when unsupported; restores Auto on shutdown.CosParams+=exposure_lock_enabled+exposure_value;CosStatus+=exposure_supported(per-camera support is known only while running, so surfaced via the polled status, not the pre-start capability probe).ShimParams/ShimStatus+ PInvoke mirrors;EffectSettingspersistence; VM observableExposureLock/ExposureValue/ExposureSupportedwith live push + config round-trip; XAML toggle + brightness slider, greyed until running and the camera reports support.The native
camControl==nullcheck is the authoritative gate (a managedApplyParamsgate would force exposure off at Start before the first status poll lands and break persisted-on exposure).Verification
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