Fix motion capture UI freezes: throttling, async camera open/scan, stale poll

Several compounding freeze sources in plugins/motion_capture/:
- tracker.py: _run_real had no frame-rate cap independent of the camera's
  configured fps (up to 120fps/2560x1440 was possible), and no bound on
  consecutive failed reads — a camera that "opens" (cv2 isOpened() can lie,
  seen with Windows MSMF/obsensor) but never actually delivers frames would
  get hammered forever. Added a 20Hz processing cap, a real test-read before
  committing to a camera, and a give-up-after-30-failures fallback to
  simulation.
- tracker.py/device.py: cv2.VideoCapture() opening a real camera is a slow,
  blocking call — CameraTracker.start() used to do this synchronously on
  the caller's thread, which froze the whole app when ProfileManager.apply()
  called it during profile load. Now runs on the background thread; status
  reporting (CameraDevice) moved to an on_result callback since the caller
  can no longer learn the outcome synchronously.
- window.py: the Camera View preview ran a 30Hz GUI-thread timer doing a
  full-frame copy + QImage/QPixmap rebuild every tick unconditionally (no
  visibility check) — dropped to 10Hz and skips entirely when hidden.
  Camera enumeration (list_cameras(), up to 8 sequential cv2.VideoCapture
  probes) also ran inline in the window constructor, blocking it open the
  same way camera_panel.py's CameraScanThread already avoided for the Add
  Device dialog — moved to the same async pattern here.

config_window.py: separately, ConfigWindow._dev_poll (device status label
refresh) was stopped in closeEvent and never restarted, since MainWindow
reuses the same ConfigWindow instance across opens — invisible before
because connect() was synchronous, but with the above change a device can
sit in CONNECTING for a while, and a stale poll made that look stuck
forever after reopening the window. Restart it in showEvent.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

1 files changed, 40 insertions, 7 deletions

diff --git a/plugins/motion_capture/window.py b/plugins/motion_capture/window.py
index 46b8850..328c61b 100644
--- a/plugins/motion_capture/window.py
+++ b/plugins/motion_capture/window.py
@@ -16,7 +16,7 @@ from typing import Optional, Tuple
 
 import numpy as np
 
-from PyQt6.QtCore import Qt, QPointF, QTimer, pyqtSignal
+from PyQt6.QtCore import Qt, QPointF, QTimer, QThread, pyqtSignal
 from PyQt6.QtGui import (
     QCloseEvent, QColor, QFont, QImage, QMouseEvent,
     QPainter, QPen, QPixmap,
@@ -27,6 +27,17 @@ from PyQt6.QtWidgets import (
 )
 
 
+# ── Background camera enumeration ───────────────────────────────────────────
+
+class _CameraListThread(QThread):
+    """Runs tracker.list_cameras() off the GUI thread — see _scan_cameras."""
+    done = pyqtSignal(list)
+
+    def run(self):
+        from tracker import list_cameras
+        self.done.emit(list_cameras())
+
+
 # ── Frame display + rubber-band selection widget ──────────────────────────────
 
 class FrameSelector(QWidget):
@@ -262,7 +273,8 @@ class MotionCaptureWindow(QWidget):
 
         self._refresh = QTimer(self)
         self._refresh.timeout.connect(self._update)
-        self._refresh.start(33)
+        self._refresh.start(100)   # 10 Hz — a position readout doesn't need 30fps,
+                                    # and this is a full-frame copy + repaint on the GUI thread
 
     # ── UI ────────────────────────────────────────────────────────────────
 
@@ -377,15 +389,31 @@ class MotionCaptureWindow(QWidget):
     # ── Actions ───────────────────────────────────────────────────────────
 
     def _scan_cameras(self):
-        from tracker import list_cameras
-        current_idx = self.get_camera_index()
+        # list_cameras() tries cv2.VideoCapture() on several indices
+        # sequentially — each one can be slow to fail (backend/driver
+        # probing), so this used to run inline here and block the whole
+        # app while the window opened. Run it on a background thread instead
+        # (same pattern camera_panel.py's CameraScanThread already uses for
+        # the Add Device dialog's scan).
+        self._pending_cam_idx = self.get_camera_index()
+        self._refresh_btn.setEnabled(False)
         self._cam_combo.blockSignals(True)
         self._cam_combo.clear()
-        self._cameras = list_cameras()
+        self._cam_combo.addItem("Scanning…")
+        self._cam_combo.blockSignals(False)
+        self._scan_thread = _CameraListThread(self)
+        self._scan_thread.done.connect(self._on_cameras_scanned)
+        self._scan_thread.start()
+
+    def _on_cameras_scanned(self, cameras: list):
+        self._refresh_btn.setEnabled(True)
+        self._cam_combo.blockSignals(True)
+        self._cam_combo.clear()
+        self._cameras = cameras
         for _, label in self._cameras:
             self._cam_combo.addItem(label)
         for i, (idx, _) in enumerate(self._cameras):
-            if idx == current_idx:
+            if idx == self._pending_cam_idx:
                 self._cam_combo.setCurrentIndex(i)
                 break
         self._cam_combo.blockSignals(False)
@@ -466,9 +494,14 @@ class MotionCaptureWindow(QWidget):
     # ── Display update ─────────────────────────────────────────────────────
 
     def _update(self):
-        if not self._connected:
+        if not self._connected or not self.isVisible():
             return
 
+        # simulated flips async now (camera opens on the tracker's background
+        # thread, see CameraTracker._open_and_run) — keep the badge in sync
+        # instead of reading a value that was still stale at Connect-time.
+        self._sim_badge.setVisible(self._tracker.simulated)
+
         if not self._selecting:
             frame = self._tracker.get_frame()
             if frame is not None: