DeeJanuz--frametop/hands/README.md

Hands (experimental, deferred)

Hand tracking from the headset's own cameras. It's deferred: it costs a lot of the headset's CPU and needs more work, so install.sh doesn't offer it and the README doesn't list it. It still builds and runs, installed by hand (below), for working on it.

It serves two things in Frametop:

• Hand cutouts: where your hand is between an eye and a screen, that eye sees the room through the screen (ft-screens, screens/handcut.cpp), so your hands show over the screens the way they do on a Vision Pro.
• Pinches and grips: with POINTER_HANDS=1, the pointer helper takes them as clicks and drags. Look at something and pinch to click it, with the eye tracker doing the looking (gaze/), or close your hand to press and drag what the pointer is on. See "Pinches and grips in the pointer" below.

Two programs, each a user service that stops when SteamVR does:

• ft-camd (camd/, C) borrows XRService's camera buffers and publishes the four IR tracking cameras' frames to a shared-memory ring. It runs on the host.
• ft-hands (track/, C++) finds hands in those frames with MediaPipe's palm and landmark models on ncnn, triangulates them, and publishes them. It runs in the dev container.

They don't start with SteamVR. hands/run.sh install builds them, gives ft-camd its capabilities, installs both services disabled, and links hands/ft-handsctl into ~/.local/bin. Then ft-handsctl on starts hand tracking and ft-handsctl off stops it. install.sh doesn't install it.

ft-handsctl on | off            # on the Frame: start or stop hand tracking (SteamVR must be running)
ft-handsctl status              # the services, and ft-hands' last status lines
ft-handsctl log [lines]
ft-handsctl cutouts on|off|state  # ft-screens' hand cutouts, without stopping tracking
ft-handsctl gestures            # pinches and grips, live (tools/watch_gestures.py --distance)

hands/run.sh install            # build, give ft-camd its capabilities (sudo, once per build), install disabled
hands/run.sh start|stop         # start or stop the services
hands/run.sh restart            # after changing a setting
hands/run.sh status
hands/run.sh log [lines]
hands/run.sh caps               # after rebuilding ft-camd (a rebuild clears its capabilities)
hands/run.sh uninstall

Settings in ~/.config/frametop.conf (FT_<name> in the environment overrides them), read when ft-camd and ft-hands start:

• HANDS_SWAP_SIDES=1: the two side cameras' names are swapped (see ft-camd below). Check with tools/check_sides.py --ring.
• HANDS_CPUS=5,6,7: the CPUs the model threads run on (below).
• HANDS_CAMERAS (auto), HANDS_BRIGHT (all), HANDS_BRIGHT_ON (40), HANDS_BRIGHT_OFF (25): which cameras ft-hands tracks with, as --cams, --bright, --bright-on and --bright-off (see ft-hands). HANDS_CAMERAS=mono also keeps ft-camd off the colour cameras.
• HANDS_COLOR_LEFT (color_video0), HANDS_COLOR_CROP (subtract): how the colour module's calibration maps onto its images, as --color-left and --color-crop.

The pointer helper's POINTER_HANDS and POINTER_PINCH_*/POINTER_GRIP_* settings are in "Pinches and grips in the pointer" below.

Files, all in /run/user/UID/frametop-hands/ (private to the user; not /run/user/UID/frametop/, which the desktop session deletes whenever it starts):

File	Written by	Layout	Read by
cam-ring	ft-camd	camd/fhring.h	ft-hands, tools/ring.py
hands	ft-hands	include/fh_hands.h	ft-screens (screens/handcut.cpp)
gestures	ft-hands	include/fh_gestures.h	the pointer helper (pointer/helper/ft-pointer.cpp), tools/watch_gestures.py

The source keeps the fh_ names and magic strings of frame-hands, the project it started as, so recordings made with it still work.

ft-camd

XRService owns the headset cameras. ft-camd borrows its DMA-BUFs read-only with pidfd_getfd, the same way FrameEyeCameraFeed does. It never touches XRService's V4L2 descriptors. discovery in camd/xrcams.c is adapted from FrameEyeCameraFeed (MIT, see camd/LICENSE.FrameEyeCameraFeed).

Polling buffers for changes can catch a frame while the camera is still writing it. Instead, ft-camd listens to the v4l2:v4l2_dqbuf tracepoint, which fires when XRService takes a buffer. It gives the buffer index, the sequence number and the capture timestamp. ft-camd learns which DMA-BUF holds each V4L2 index by watching which buffer changes at each dequeue:

• Right after XRService allocates its buffers, the mapping is allocation order.
• After XRService restarts streaming, the order is shuffled, and the mapping is learned index by index.
• The two upper cameras share one run of buffers. For them, only allocation order can tell the cameras apart.
• It also re-maps an index on the fly when its buffer holds no new frame.

Privileges. Setting up needs three things. pidfd_getfd on XRService needs CAP_SYS_PTRACE, because the Frame has ptrace_scope=1. The system-wide tracepoint needs CAP_PERFMON, because perf_event_paranoid is 2. Its format files are root-only, which needs CAP_DAC_READ_SEARCH. hands/run.sh install gives the binary those capabilities with sudo setcap. File capabilities need a filesystem mounted without nosuid. The Frame's /home (ext4) has no nosuid. ft-camd drops them all once it has set up, before it reads a frame, and then runs as you. XRService runs as you too. It also runs under sudo, for trying it by hand, and then drops to the user who ran sudo. It reads nothing from the ring's readers.

The ring is mode 0600, in a folder only you can write. Frame handling:

• Only complete, bright frames are published. The cameras alternate a normal exposure with a near-black one, so each camera gets 30 of its 60 fps.
• A copy torn by the camera overwriting the buffer is dropped.
• Each copy takes about 0.1 ms, and a cache sync about 0.15 ms.

Options:

• --dark R: a frame dimmer than R times the camera's recent brightest counts as near-black. Default 0.4.
• --with-dark: also publish the near-black frames, as extra ring cameras flagged FH_CAM_DARK. They show only light sources, so they're no use for hands.
• --with-color: also publish the two Arcturus colour cameras, flagged FH_CAM_COLOR. The service leaves it off and runs the mono cameras only (see "Known issues"). To try the colour cameras, add it to ExecStart in hands/frametop-camd.service and run hands/run.sh install again; ft-hands then picks the cameras by the light. Each is the luma of the 10-bit frame's valid 1972x2464 (the top 8 bits), at half size (--color-scale 2: 986x1232). They run at --color-idle (2 fps), enough for ft-hands to tell how bright it is, until a reader asks for more in /run/user/UID/frametop-hands/color-fps (ft-hands writes 30 while it tracks or records with them), up to --color-fps (30; the cameras run at 60). HANDS_CAMERAS=mono leaves them out. Frames that carry the module's warped half-size copy are dropped. Their capture_ns is on the colour module's clock (2.2 s off the mono cameras' on 2026-09-29), so line them up with the mono cameras by dqbuf_ns. Each frame costs about 0.65 ms of cache sync and 1.1 ms of decoding, so both cameras at 30 fps take about 11% of a core.
• Each mono camera's latest near-black frame's mean goes in the ring (dark_mean): a short fixed exposure, so it follows the room's IR light, sunlight above all.
• The ring holds 8 cameras: 4 mono, plus 4 dark twins or 2 colour cameras.
• Colour isn't reliable yet. In the lit-room test of 2026-09-30, the colour cameras kept losing their buffer mapping while the headset was worn: 30 frames in a row looked unchanged, the camera relearned, and after 5 relearns ft-camd exited. Each relearn probed all 32 colour buffers, a whole-buffer cache sync each, which also made the mono cameras miss frames. Runs with the headset idle had none of this. So the passthrough compositor may be writing into the colour buffers while Room View shows. Since then a colour camera never takes the mono ones down: it probes at most 4 buffers a frame, and one that goes stale twice in a row is paused (10 s, doubling up to 160 s) and learned again, without ft-camd exiting. Whether a frame is new is judged on the luma rows only: the chroma after them hardly changes in a lit room.
• FT_CAMD_DEBUG=1 in the environment: at each stale colour frame, ft-camd logs to stderr the camera, the frame's time, V4L2 index and sequence number, and, for every candidate buffer, how many of its sampled words changed, in all and in the last eighth of the samples.
• --sensor S: only the mono cameras whose sensor name contains S.
• --status S: a status line every S seconds (0: never).

It exits when XRService exits, or when a camera's buffers keep going stale, which means XRService has reallocated them. The service starts it again, and it attaches to the new buffers.

Which camera is which: video9 is slam_left, video13 is slam_right, video6 is upper_left and video7 is upper_right. This was checked by rendering the same view from each camera with the factory calibration. But ft-camd tells the side cameras' buffers apart only by XRService's allocation order, and after some XRService restarts it gets them backwards. Then every hand is seen by one camera only, at the wrong depth, and the hand holes land beside the hands. With the headset on, looking at a room with some texture, tools/check_sides.py --ring says whether the names are right (exit 0), swapped (exit 3), or it can't tell (exit 2). When they're swapped, set HANDS_SWAP_SIDES=1. The colour cameras are video3 (arcimx616 0-0010) and video0 (0-001a); which of them is passthrough_left in the module's calibration is for tools/check_color.py to settle, on a recording with texture in view.

ft-hands

hands/build/ft-hands                  # status every 5 s; Ctrl+C to stop
hands/build/ft-hands --int8           # the 8-bit models (models/ncnn/*-int8.ncnn.*)

Run it in the dev container (distrobox enter dev -- ...). It reads the factory calibration from /persist (/run/host/persist in the container).

Options:

• --threads N: model threads, pinned to the --cpus list. Default 3.
• --cpus LIST: CPUs for the model threads and the main loop. Default 5,6,7 (HANDS_CPUS). SteamOS starts user processes on CPUs 0-4, and XRService's head tracking runs on 2-3. With the headset on, a step took 8.4 ms on 5-7 against 13.2 ms on 2-4, and SteamVR's frame timing didn't change (2026-09-29, three rounds of the same replayed frames).
• --contrast MODE or PALM/HAND: how crops are equalized before the models see them: clahe[:CLIP], none, or stretch (1st-99th percentile). Default clahe:2/none. In the dim recording, CLAHE let the palm search find about 10% more hands, but it made the landmarks jitter more (published median 6.9 mm, against 6.0 mm with plain landmark crops).
• --swap-sides: swap the two side cameras (HANDS_SWAP_SIDES, see ft-camd).
• --seconds N: stop after N seconds.
• --status S: how often to print status, in seconds.
• --models DIR: where the models are.
• --nice N: niceness. Default 5, so the VR stack wins contested CPUs.
• --no-publish: don't write the hands and gestures files.
• --record DIR, --record-for S: save every frame set for S seconds (default 120) to DIR/sets.bin. That's about 80 MB/s. Sending the tracker SIGUSR1 (pkill -USR1 -x ft-hands) starts a recording in ~/.local/share/frametop/hands/rec-<time> without a restart. Recordings are images of your hands and room: they stay on the headset unless you move them.
• --record-only: record without tracking or publishing, so it can run beside the live tracker. Give it --record DIR, since SIGUSR1 would reach both trackers. With ft-camd --with-dark, recordings also hold each camera's newest dark frame as <name>_dk, which doubles the rate. With --with-color, each colour camera's newest frame is saved with every set, as color_video<N>, which adds about 70 MB/s. Run the recorder at normal I/O priority: idle I/O priority stalled a 165 MB/s recording.
• --keep-presence P: the landmark presence a tracked view needs to stay tracked. New views always need 0.5. Default 0.5. Lowering it to 0.2 barely helped in the bright recording, because lost hands drop to near-zero presence.
• --ring PATH: read frames from another ring, such as ft-ringplay's.
• --cams auto|mono|color|all (HANDS_CAMERAS, default auto): which cameras to track with. The mono IR cameras light the hands themselves and track well in dim rooms, but in bright light they expose for the room and the hands come out dark. The colour pair is the other way round. auto goes by the colour frames' mean brightness: at --bright-on (HANDS_BRIGHT_ON, 40) or over for 2 s it tracks with --bright (HANDS_BRIGHT: all, every camera, the default, or color), and under --bright-off (HANDS_BRIGHT_OFF, 25) for 2 s with the mono cameras again. A dim evening room read 9. The switch is logged (cameras: mono -> all (...)), and the status line gives the colour level, the mono cameras' ambient IR, and how many steps had colour frames. Colour frames arrive on their own schedule, so a step holds the mono set, the colour pair, or both, and views wait in their camera for its next frame. With no colour cameras in the ring (ft-camd without --with-color, as the service runs it), ft-hands tracks with the mono cameras whatever this says.
• --color-left NODE (HANDS_COLOR_LEFT, color_video0) and --color-crop subtract|none (HANDS_COLOR_CROP, subtract): how the colour module's calibration maps onto the images. Not settled yet: tools/check_color.py on a recording with a lit, textured view tells.
• --grip-begin R, --grip-end R: the grip detector (below). Defaults 1.2 and 1.45.
• --gesture-log: print what the pinch and grip detectors measure, 10 times a second: each hand's thumb-to-index distance (world and triangulated), its palm-down reading and its finger curl.

Gestures (/run/user/UID/frametop-hands/gestures, include/fh_gestures.h), for the pointer helper:

• A pinch: the thumb and index tips within 2 cm, ending past 3.5 cm (see "Pinch" below).
• A grip, a closed hand: every finger's tip nearer the wrist than 1.2 times its knuckle is (from the model's 3D hand, so hand size doesn't matter), ending when they open past 1.45 on average. It begins only on a hand seen open within the last second (closing it is the gesture), with the palm at most 35 degrees below straight ahead and at least 15 cm in front of the eyes, and not with the thumb within 3 cm of the index tip (that's a pinch with the other fingers curled). A grip ends a pinch on the same hand, as lost. In the 2026-09-30 lit recording (no deliberate fists), the checks cut false grips from 14 to 6, all with the hands on the desk while looking down at it. The pointer helper ignores grips that begin more than POINTER_GRIP_BELOW (0.35 m) below the eyes, which it can tell and ft-hands can't.
• tools/watch_gestures.py --distance shows both live; ft-handreplay --timeline logs them and each hand's finger curl.

The status line also says how often a hand was on each side (by where the wrist is), and why views and hands came and went: views lost (the landmark model stopped seeing the hand), handoff misses (a crop projected from the hand's 3D position found nothing), duplicates, splits (two views disagreed in 3D), and hands created, merged and forgotten.

Scheduling

• Each hand is tracked in its best two cameras, the way MediaPipe tracks: the landmark model runs on a crop placed from the previous landmarks, with no palm detection.
• A hand seen in too few cameras is projected into the others through the calibration. Where it lands well inside a camera, that camera gets a crop to try. This is how a hand raised out of the side cameras reaches the upper ones.
• The palm detector runs only while fewer than two hands are tracked, at most 5 times a second, on a few zoomed tiles per search. Tiles are picked in proportion to how likely hands are there. Each tile is turned so the expected shoulder-to-hand direction points up.
• Frame sets are processed at 30 Hz while a hand moves faster than 0.25 m/s (or a pinch is down or closing), at 15 Hz otherwise, and at 5 Hz while no hand is in view.

3D

• Two or more views: each landmark is triangulated from the camera rays, weighted by the model's presence score. The median ray distance is reported as the residual.
• Pairing views across cameras. The side cameras sit side by side, so two hands next to each other at the same height fall on the same epipolar lines, and rays to two different hands can nearly meet close to the cameras. That made phantom hands 12-15 cm in front of the eyes, which tore holes through the screens. Each step now scores every way of pairing the views in two cameras and keeps the best. A pair scores well when its rays meet, when each view's apparent size matches the triangulated distance, and when the model calls both the same hand. The size check uses a fixed prior: with the model's average hand, clean pairs measure 0.71-1.51 times the one-view distance, and mismatched pairs mostly far less.
• One view: depth comes from the model's metric world landmarks, their spread across the palm against the angle it covers in the image, scaled by the user's hand size (learned while two views are available). That distance is off by 10-30% and wanders about 10% between frames, so a hand that drops to one camera keeps its last distance and drifts toward the one-view guess by 10% a frame.
• Smoothing. The published landmarks go through a One Euro filter: it smooths hard while the hand is still (tracking noise is several mm per frame) and hardly at all while it moves fast. The palm speed that sets the update rate is the filtered one; the raw speed read about 0.25 m/s from noise alone.
• Capsules. Forearms follow the hand's own axis, and nothing within 12 cm in front of the eyes is published.

How good the depth is, measured from recordings (2026-09-30, --depth below): the two lower cameras see the hands about 77% of the time, a lower and an upper camera 7-12%, and one camera 12-15%. Depth is the noisy direction. With the lower pair, it jitters 4-6 times as much as sideways position (published: 3-7 mm against 1-2 mm). The one-camera guess is a median 2-6 cm off. When a camera drops out, drifting 10% a frame toward that guess is worse than keeping the last distance (after 0.5 s a median 23-30 mm off, against 11-12 mm).

Pinch

ft-hands detects a pinch per hand (track/pinch.h) and publishes it to the gestures file. The layout, and how to read it without missing quick taps, is in include/fh_gestures.h.

• A pinch begins when the thumb and index tips come within --pinch-begin (default 0.020 m). It ends when they open past --pinch-end (0.035 m) for 2 processed frames in a row, or when the hand stays lost for 0.25 s (flagged lost).
• The distance comes from MediaPipe's world landmarks: the model's own 3D hand pose, averaged over the hand's views, at the user's hand size. --pinch-triangulated uses the triangulated tips instead. On two recordings without deliberate pinches, the world landmarks came under 2 cm in 0.2-1% of frames, against 3.3-4.5% for the triangulated tips. In the dim recording, typing still gave 2 pinches a minute (see the next point).
• --pinch-palm-down MAX holds back pinches begun with the palm facing down (MAX is the palm normal's share of the head's up axis). The default, 1, turns it off. A close held back that way has to open again before a pinch can begin. Typing curls the thumb onto the index: in the lit recording of 2026-09-30, typing on a keyboard in the lap began 23 pinches in about 2 minutes, all with the palm facing down (0.69-1.00), while the 26 deliberate ones read 0.00-0.50. But in the headset, deliberate pinches with the hand raised in front read 0.90-0.99 too, so the limit is off. Typing is caught by the pointer helper instead: the input relay tells it when you press a key, and no pinch begins within POINTER_PINCH_TYPING of one.
• A hand a pinch is down on stays with that side until the pinch ends. The left/right call is a running average of the model's, and when it flipped mid-pinch, the other side took the same hand and both sides pinched at once.
• The pinch point is between the index and middle knuckles, which hold still while the fingers open and close. The tips' midpoint moved 1-2 cm as a pinch opened, which dragged every release off its press. A drag is the pinch point now, minus where it was when the pinch began, both turned into the room with the HMD pose at their capture times.
• tools/watch_gestures.py prints begins, ends and drag offsets live, and --distance prints each hand's distance.

Pinches and grips in the pointer

With POINTER_HANDS=1, the pointer helper (pointer/helper/ft-pointer.cpp) reads the gestures file every frame. It's off by default.

• Pinch to click. In gaze mode a pinch works like the mouse's press: the pointer stops where the gaze put it, and the click comes when the pinch opens, where the pointer is then. A quick tap clicks where you looked. Held, the pinching hand moves the pointer to correct the gaze, and the correction is a lesson for the gaze tracker, as with the mouse.
• Without gaze mode, a pinch is a real press, like the mouse's button: pressed when it closes, released when it opens, and while it's held the hand drags the pointer. A tap is still a click where the pointer is.
• Grip to drag. Closing the hand presses where the pointer is, the hand moves the pointer, and opening the hand releases. So a title bar moves its window, a panel's grab bar carries the panel, and text gets selected.
• A pinch ended by losing the hand, or by a grip taking over, doesn't click.
• The hand's movement is taken in the room, from where the eye was when the gesture began, so turning your head doesn't move the pointer. The first gesture while the pointer is off only wakes it. Gestures are ignored in a VR game (unless the dashboard is up), with the headset off, and while the mouse's button is held.

Settings in ~/.config/frametop.conf:

• POINTER_HANDS (0): 1 turns pinches and grips on.
• POINTER_PINCH_GAIN (0.5): a held pinch moves the pointer this many times the hand's angle, seen from the eye. Under 1 gives precision.
• POINTER_PINCH_DEADZONE (1.5): how many degrees the pinching hand moves before the pointer does, so a tap's jitter and the pinch point shifting as the fingers close don't move it.
• POINTER_GRIP_GAIN (1): a grip moves the pointer this many times the hand's angle.
• POINTER_GRIP_BELOW (0.35): grips that begin more than this many metres below the eyes are ignored, because hands resting on a desk curl like a loose fist. Pinches have no such limit: deliberate ones sat 0.35-0.45 m below the eyes with the elbow resting.
• POINTER_PINCH_TYPING (1): no pinch begins within this many seconds of a key press, because typing touches thumb to index.

Recordings

hands/build.sh --tools also builds the offline tools.

ft-handreplay DIR runs a recording through the tracker with the live scheduling and reports how well it kept the hands: hands per set, left and right coverage, track lengths, pinches, jitter, and the same reasons as the status line.

hands/build/ft-handreplay ~/.local/share/frametop/hands/rec-20260929-120000 --cost --oracle 10 --timeline /tmp/tl.txt

• --cost: instead of timing the steps, charge each round of model calls what it typically costs live (10 ms landmarks, 18 ms palms), so results repeat exactly.
• --oracle N: every N-th set, also search every tile of every camera, and report how often the tracker had the hands that full search could find.
• --slow F: live, the tracker skips sets that arrive while it's busy. Replay counts each step's time times F as busy (default 1; the headset is busier live).
• --timeline FILE: a line per processed set and hand, with pinch events and distances.
• --cams mono|color|all: which cameras to track with (default mono). color tracks with the Arcturus pair alone, for comparing it with the IR cameras on the same recording. It needs a recording made with ft-camd --with-color. --color-left NODE (color_video0 or color_video3) and --color-crop subtract|none say how the module's calibration maps onto the images; tools/check_color.py finds out.
• --depth FILE: a line per hand per processed set for tools/depth_report.py, which measures the depth without ground truth: how the hands were seen, the noise along the line of sight against across it, each camera's one-view distance against the triangulated one, and what a camera dropping out would do.
• The pinch, contrast and presence options are ft-hands'.

ft-ringplay DIR --ring PATH [--from S] [--to S] [--loop] publishes a recording into a ring file in real time, as ft-camd would, so ft-hands --ring PATH --no-publish runs the same frames run after run. It needs no privileges, and it skips the dark frames.

Tools

Python, with NumPy and OpenCV. setup/dev-container.sh doesn't install them, because Fedora's python3-opencv pulls in over a gigabyte; in the dev container, run sudo dnf install python3-numpy python3-opencv once. Off the Frame, FRAME_JOB_DEVICE_ROOT can point at a folder with copies of the headset's calibration files.

• tools/check_sides.py --ring (or a recording): are the side cameras named right?
• tools/check_color.py REC: how the colour module's calibration maps onto its images.
• tools/show_set.py REC: a recording's frame sets as images.
• tools/watch_gestures.py [--distance]: pinches and grips, live.
• tools/depth_report.py DEPTH: the depth measures above.
• tools/cut_sets.py REC OUT [--sets N | --at I,J,...]: copies a few frame sets (by default 8, spread evenly) out of a recording into a small one, to look at or check elsewhere without moving gigabytes. Plain Python, so it also runs on the Frame's host.
• tools/convert_models.py: how models/ncnn was made from the OpenCV Zoo ONNX ports of MediaPipe's models (see models/NOTICE).

To try the hand cutouts without restarting the desktop, screens/build/ft-handtest [--distance m] [--width m] [--seconds s] (built by screens/build.sh, run in the dev container, with hand tracking on) shows a test panel of its own, a light grid 1 m wide and 0.8 m ahead by default, and cuts your hands out of it the way ft-screens cuts them out of the screens.

Build

hands/build.sh builds in the dev container on the Frame, into hands/build/, with hands/Makefile. The first build fetches ncnn at a pinned tag (NCNN_TAG in the Makefile) and builds it into hands/build/ncnn, which takes a few minutes; NCNN=DIR points at an ncnn install already built instead. ft-camd is linked statically, because it runs on the host, which has an older glibc than the container.

Known issues

• The side cameras can come out swapped. ft-camd tells the side cameras' buffers apart only by XRService's allocation order, and some XRService restarts reverse it. For now it's caught by hand: tools/check_sides.py --ring, then HANDS_SWAP_SIDES=1. It needs a fix in ft-camd, or at least an automatic check when it starts.
• The colour cameras can't be used while the headset is worn. The colour module then writes only a half-size image into the top-left quarter of its buffers, and ft-camd drops those frames. So the service runs the mono cameras only, and tracking in bright light, where the mono cameras see dark hands, doesn't get the colour pair's help.
• The colour calibration mapping isn't settled. Which colour camera is passthrough_left (HANDS_COLOR_LEFT) and how the module's crop applies (HANDS_COLOR_CROP) still need tools/check_color.py on a recording with a lit, textured view.
• Depth when one camera loses the hand. A hand seen in one camera drifts 10% per update toward the one-camera depth guess (kMonoDepthGain, 0.1, in track/tracker.cpp). In the 2026-09-30 replays that was worse than keeping the last distance (see "3D" above). A smaller gain, such as 0.02, is the next thing to try.
• Pinches aren't reliable enough for everyday use yet. That's why hand tracking stays off until ft-handsctl on, and POINTER_HANDS is 0 by default.
• Floating windows don't get hand cutouts. Their panels show crops of the client buffer, which the cutouts' side-by-side buffer doesn't match (screens/vr.cpp, UpdateCutouts).