Keep the gaze going when the tracker loses one eye

Live, the tracker had lost the left eye (openness 0, set 2's eyes 9 to 14
degrees apart) and ft-gazed dropped 96% of samples as blinks. A blink is now
both eyes closing, each judged against its own recent good readings, and the
service defaults to mmap set 1, SteamVR's combined gaze, which keeps going
with one eye. With set 2, one-eye samples are still dropped, since its
combined direction is off by half of what the lost eye reads.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

gaze/ft-gazed

@@ -3,8 +3,13 @@
 
 Runs ft-gaze (in the dev container), and for every eye tracker sample (90 Hz):
 
-  1. drops blinks and moments the tracker lost an eye: openness under half its running
-     median, or the angle between the eyes jumping more than 1.5 degrees from its median;
+  1. drops blinks: both eyes' openness under half its running median (each eye its own).
+     With the default source, mmap set 1, that's all: set 1 is SteamVR's combined gaze,
+     which keeps going when the tracker loses one eye (its two directions stay together).
+     Set 2's combined direction is the mean of the eyes' own, so with one eye lost it's
+     off by half of whatever that eye reads (9 to 14 degrees apart were seen): with set 2,
+     samples with an eye under its floor, or the angle between the eyes jumping more than
+     1.5 degrees from its median, are dropped too;
   2. smooths it with a fixation lock (the running mean of the current fixation, 1 degree);
   3. corrects it: the calibration from ft-gazeprobe (calibration.json, reloaded when the
      probe changes it) plus what the pointer's corrections have taught since (LiveCorrection,
@@ -31,7 +36,8 @@ Control socket: abstract unix datagram "@ft_gazed":
   forget                           drop what the lessons taught (the calibration stays)
   reload                           read calibration.json again
 
-Options: --source action|mmap1|mmap2 (default mmap2, the quietest), -v (a status line every
+Options: --source action|mmap1|mmap2 (default mmap1; set 2 was a little quieter in the probe,
+but loses the pointer whenever the tracker loses an eye), -v (a status line every
 5 s on stderr), --to NAME (send the gaze to the abstract socket @NAME instead of the pointer
 helper; for testing: a helper without gaze mode forwards what it doesn't know to its driver).
 """
@@ -83,9 +89,9 @@ class Service:
         self.live.wear_time = self.steam.worn()
         self.live.refit(self.base, self.mode)
         self.fix = Fixation(radius=1.0)
-        self.opens = deque(maxlen=90)
+        self.opens = (deque(maxlen=90), deque(maxlen=90))  # left, right
         self.vergence = deque(maxlen=90)
-        self.counts = {"samples": 0, "sent": 0, "dropped": 0, "lessons": 0, "refused": 0}
+        self.counts = {"samples": 0, "sent": 0, "blinks": 0, "one_eye": 0, "dropped": 0, "lessons": 0, "refused": 0}
         self.last_sample = 0.0
         self.last = None
 
@@ -232,18 +238,30 @@ class Service:
         m1 = s["src"].get("mmap1") or {}
         o = m1.get("open")
         lr = src.get("lr", m1.get("lr"))
-        if o:
-            self.opens.append(min(o))
-        if lr is not None:
-            self.vergence.append(lr)
-        # Blinks and dropouts, judged against the last second (see steady_samples: relative,
+        # Blinks and lost eyes, judged against the last second (see steady_samples: relative,
         # because the lids come down looking down, and the vergence depends on distance).
-        if o and len(self.opens) >= 30 and min(o) < max(0.12, 0.5 * statistics.median(self.opens)):
-            self.counts["dropped"] += 1
-            return
-        if lr is not None and len(self.vergence) >= 30 and abs(lr - statistics.median(self.vergence)) > 1.5:
-            self.counts["dropped"] += 1
+        # An eye's floor comes from its good readings, so a lost eye doesn't drag it to 0.
+        low = [False, False]
+        if o and len(o) == 2:
+            for k in (0, 1):
+                hist = self.opens[k]
+                good = [v for v in hist if v >= 0.12]
+                floor = max(0.12, 0.5 * statistics.median(good)) if len(good) >= 30 else 0.12
+                low[k] = o[k] < floor
+                hist.append(o[k])
+        if all(low):
+            self.counts["blinks"] += 1
             return
+        if any(low):
+            self.counts["one_eye"] += 1
+        if self.source == "mmap2":
+            jump = (lr is not None and len(self.vergence) >= 30
+                    and abs(lr - statistics.median(self.vergence)) > 1.5)
+            if lr is not None and not any(low):
+                self.vergence.append(lr)
+            if any(low) or jump:
+                self.counts["dropped"] += 1
+                return
         # The fixation lock works in degrees here (1 degree per "pixel").
         fy, fp = self.fix(src["hy"], src["hp"], s["t"], 1.0)
         cy, cp = self.correction(fy, fp)
@@ -342,7 +360,7 @@ class Service:
 
 def main():
     ap = argparse.ArgumentParser(description="The gaze service: corrected eye tracking for the pointer")
-    ap.add_argument("--source", choices=["action", "mmap1", "mmap2"], default="mmap2")
+    ap.add_argument("--source", choices=["action", "mmap1", "mmap2"], default="mmap1")
     ap.add_argument("-v", "--verbose", action="store_true")
     ap.add_argument("--to", default="ft_pointer_helper", help="abstract socket to send the gaze to")
     args = ap.parse_args()