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session_logger.py
Phase 1: logs the live gaze stream to a per session file.
Writes one line of JSON per frame to:
sessions/live/gaze_log.jsonl
Fields per line:
t wall clock seconds (time.time()). Same epoch the browser uses
via Date.now()/1000, so gaze and DOM logs align by time.
sx, sy gaze in calibration screen space (SCREEN_W x SCREEN_H)
fx, fy gaze as a fraction of the screen (0..1). Phase 4 multiplies
these by the browser viewport size to land on a real element.
The file is truncated on each run, so one tracker run equals one clean session.
"""
import os
import json
import time
class GazeLogger:
def __init__(self, screen_w, screen_h, session_dir=os.path.join("sessions", "live")):
self.screen_w = float(screen_w)
self.screen_h = float(screen_h)
os.makedirs(session_dir, exist_ok=True)
self.session_dir = session_dir
self.gaze_path = os.path.join(session_dir, "gaze_log.jsonl")
# "w" truncates: each run starts a fresh gaze log
self._f = open(self.gaze_path, "w", buffering=1)
meta = {
"type": "meta",
"screen_w": screen_w,
"screen_h": screen_h,
"t": round(time.time(), 4),
}
self._f.write(json.dumps(meta) + "\n")
print(f"[GazeLogger] writing gaze stream to {self.gaze_path}")
def log(self, sx, sy, t=None):
if t is None:
t = time.time()
fx = sx / self.screen_w if self.screen_w else 0.0
fy = sy / self.screen_h if self.screen_h else 0.0
rec = {
"type": "gaze",
"t": round(t, 4),
"sx": round(float(sx), 2),
"sy": round(float(sy), 2),
"fx": round(float(fx), 5),
"fy": round(float(fy), 5),
}
self._f.write(json.dumps(rec) + "\n")
def close(self):
try:
self._f.close()
print(f"[GazeLogger] gaze log closed: {self.gaze_path}")
except Exception:
pass |