fix: rewrite viz as event-driven with zero-latency MIDI rendering

- Remove frame loop latency: render and send immediately on MIDI event
- Remove decay: notes on/off based purely on MIDI note-on/note-off
- Background 5 FPS refresh: catch router-dropped frames
- active_notes uses set instead of dict with decay counters
- Simpler stats: FPS, active notes, midi events processed

scripts/led-matrix-viz.py

@@ -1,20 +1,18 @@
 #!/usr/bin/env python3
 """Listen for MIDI events via UDP and display note activity on LED matrix.
 
-Non-blocking I/O with proper POLLOUT queue, instrumentation, and fast rendering.
+Event-driven: renders and sends frame immediately on each MIDI event.
+Background 5 FPS refresh catches any lost frames from the router.
 """
-import socket, msgpack, time, os, select, collections
+import socket, msgpack, time, os, select
 
 VIZ_PORT = int(os.environ.get("VIZ_PORT", "8082"))
 ROUTER_SOCK = os.environ.get("ROUTER_SOCK", "/var/run/arduino-router.sock")
-DECAY_FRAMES = int(os.environ.get("DECAY_FRAMES", "3"))
-MAX_NOTE_AGE = int(os.environ.get("MAX_NOTE_AGE", "15"))
 
 COLS = 13
 ROWS = 8
 
-frame_interval = 1.0 / 30.0  # 30 FPS target
-next_frame_time = 0.0
+REFRESH_INTERVAL = 0.2  # 5 FPS background refresh (catches dropped frames)
 
 STATS_FILE = "/tmp/viz-stats.json"
 _poll = select.poll()
@@ -35,25 +33,15 @@ def pack_frame(pixels):
             (bits >> 64) & 0xFFFFFFFF, (bits >> 96) & 0xFFFFFFFF)
 
 
-class FrameQueue:
-    def __init__(self, maxsize=10):
-        self._q = collections.deque()
-        self._maxsize = maxsize
-
-    def push(self, frame_bytes):
-        if len(self._q) >= self._maxsize:
-            return False  # dropped
-        self._q.append(frame_bytes)
-        return True
-
-    def pop(self):
-        return self._q.popleft() if self._q else None
-
-    def __len__(self):
-        return len(self._q)
-
-    def full(self):
-        return len(self._q) >= self._maxsize
+def render(active_notes):
+    pixels = [[0] * COLS for _ in range(ROWS)]
+    note_min, note_max = 36, 96
+    for note in active_notes:
+        row = 7 - int((note - note_min) / (note_max - note_min) * 7)
+        row = max(0, min(7, row))
+        col = note % 12
+        pixels[row][col] = 1
+    return pack_frame(pixels)
 
 
 def connect_router():
@@ -66,9 +54,20 @@ def connect_router():
     return router
 
 
-def main():
-    global next_frame_time
+def send_frame(router, packer, msg_id, frame):
+    if frame is None:
+        return msg_id
+    msg_id = (msg_id + 1) % 65535
+    params = [str(v) for v in frame]
+    req = packer.pack([0, msg_id, "draw_frame", params])
+    try:
+        router.sendall(req)
+    except (BlockingIOError, OSError):
+        pass
+    return msg_id
 
+
+def main():
     sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
     sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
     sock.bind(("0.0.0.0", VIZ_PORT))
@@ -78,29 +77,30 @@ def main():
     packer = msgpack.Packer()
 
     _poll.register(sock, POLLIN)
-
-    active_notes = {}
-    last_frame = None
-    buf = b""
-    msg_id = 0
-    next_frame_time = time.monotonic()
-
-    pending_frames = FrameQueue(maxsize=5)
     router_fd = router.fileno()
     _poll.register(router, POLLIN | POLLOUT)
 
+    active_notes = set()
+    last_sent_frame = None
+    pending_frame = None
+    buf = b""
+    msg_id = 0
+
     frames_sent = 0
     frames_dropped = 0
     router_errors = 0
+
+    last_refresh = time.monotonic()
     stats_last_write = time.monotonic()
     fps_sample_start = time.monotonic()
     fps_sample_frames = 0
+    events_processed = 0
 
     while True:
         now = time.monotonic()
+        refresh_due = (now - last_refresh) >= REFRESH_INTERVAL
 
-        timeout = max(0, int((next_frame_time - now) * 1000))
-        timeout = min(timeout, 5)  # 5ms max to stay responsive
+        timeout = 5  # ms
 
         try:
             events = _poll.poll(timeout)
@@ -126,10 +126,20 @@ def main():
                         note = int(parts[2])
                         vel = int(parts[3]) if len(parts) >= 4 else 0
                         msg_type = status & 0xF0
+                        changed = False
                         if msg_type == 0x90 and vel > 0:
-                            active_notes[note] = {"decay": DECAY_FRAMES, "age": 0}
+                            if note not in active_notes:
+                                active_notes.add(note)
+                                changed = True
                         elif msg_type == 0x80 or (msg_type == 0x90 and vel == 0):
-                            active_notes.pop(note, None)
+                            if note in active_notes:
+                                active_notes.discard(note)
+                                changed = True
+                        if changed:
+                            events_processed += 1
+                            frame = render(active_notes)
+                            if frame != last_sent_frame:
+                                pending_frame = frame
 
             # Process router readable
             if fd == router_fd and (flags & POLLIN):
@@ -141,84 +151,43 @@ def main():
                 except BlockingIOError:
                     pass
 
-            # Process router writable — drain pending frames
-            if fd == router_fd and (flags & POLLOUT):
-                frame = pending_frames.pop()
-                if frame:
-                    try:
-                        router.sendall(frame)
-                        frames_sent += 1
-                    except (BlockingIOError, OSError):
-                        frames_dropped += 1
-                        router_errors += 1
-                        pending_frames.push(frame)
-                        time.sleep(ROUTER_RECONNECT_DELAY)
-                        old_fd = router_fd
-                        try:
-                            router.close()
-                        except OSError:
-                            pass
-                        router = connect_router()
-                        router_fd = router.fileno()
-                        try:
-                            _poll.unregister(old_fd)
-                        except (KeyError, OSError):
-                            pass
-                        _poll.register(router, POLLIN | POLLOUT)
+        # Router writable: send pending frame immediately
+        if pending_frame is not None:
+            if any(fd == router_fd and (flags & POLLOUT) for fd, flags in events):
+                msg_id = send_frame(router, packer, msg_id, pending_frame)
+                last_sent_frame = pending_frame
+                pending_frame = None
+                frames_sent += 1
+            else:
+                frames_dropped += 1
 
-        # Render frame when due
-        if now >= next_frame_time:
-            next_frame_time = now + frame_interval
+        # Background refresh: resend last frame to recover from router drops
+        if refresh_due:
+            last_refresh = now
             fps_sample_frames += 1
+            if last_sent_frame is not None:
+                msg_id = send_frame(router, packer, msg_id, last_sent_frame)
 
-            pixels = [[0] * COLS for _ in range(ROWS)]
-            expired = []
-            for note, state in list(active_notes.items()):
-                state["age"] += 1
-                state["decay"] -= 1
-                if state["decay"] <= 0 or state["age"] > MAX_NOTE_AGE:
-                    expired.append(note)
-                    continue
-                note_min, note_max = 36, 96
-                row = 7 - int((note - note_min) / (note_max - note_min) * 7)
-                row = max(0, min(7, row))
-                col = note % 12
-                pixels[row][col] = 1
-
-            for note in expired:
-                del active_notes[note]
-
-            frame = pack_frame(pixels)
-            if frame != last_frame:
-                msg_id = (msg_id + 1) % 65535
-                params = [str(v) for v in frame]
-                req = packer.pack([0, msg_id, "draw_frame", params])
-                if pending_frames.push(req):
-                    pass  # queued
-                else:
-                    frames_dropped += 1
-                last_frame = frame
-
-            # Write stats periodically (every 2s)
+            # Write stats every 2s
             if now - stats_last_write >= 2.0:
                 fps = fps_sample_frames / (now - fps_sample_start) if (now - fps_sample_start) > 0 else 0
-                _write_stats(frames_sent, frames_dropped, pending_frames, fps, len(active_notes))
+                _write_stats(frames_sent, frames_dropped, fps, len(active_notes), events_processed)
                 stats_last_write = now
                 fps_sample_start = now
                 fps_sample_frames = 0
+                events_processed = 0
 
 
-def _write_stats(sent, dropped, pending, fps, active_count):
+def _write_stats(sent, dropped, fps, active_count, events):
     import json
     try:
         with open(STATS_FILE, "w") as f:
             json.dump({
                 "frames_sent": sent,
                 "frames_dropped": dropped,
-                "pending_queue": len(pending),
-                "queue_full": pending.full(),
                 "fps": round(fps, 1),
                 "active_notes": active_count,
+                "midi_events": events,
                 "ts": time.time()
             }, f)
     except OSError: