kmsgrab e ScreenShot2: esiti sperimentali documentati

- kmsgrab non praticabile: piano primario AR30 con modifier AMD DCC/tiled, ffmpeg
  rifiuta il framebuffer prima di applicare format/modifier
- KWin ScreenShot2: NoAuthorized anche con desktop entry system-wide
- indicatore del vassoio identificato come SNI di xdg-desktop-portal-kde
  (titolo 'Trasmissione dello schermo')
- backend kmsgrab comunque implementato e selezionabile (capture=kmsgrab)
- setup-kmsgrab.sh: installa via pkexec una copia di ffmpeg con cap_sys_admin+ep

backend/ambilightd.py

@@ -42,6 +42,8 @@ DEFAULTS = {
     "baud": 115200,
     "fps": 60,
     "side": "top",         # top | bottom
+    "capture": "portal",   # portal (ScreenCast) | kmsgrab (DRM diretto, senza indicatore)
+    "drm_device": "/dev/dri/card1",
     "auto_start": True,    # streaming attivo all'avvio del demone
 }
 PARAM_RANGES = {
@@ -190,32 +192,53 @@ def apply_params(zones, cfg):
 
 
 def capture_loop(state, strip):
-    from ambicapture import Capture, screencast_stream
+    """Ciclo di cattura: sceglie il backend (portal o kmsgrab) e invia i frame."""
+    from ambicapture import Capture, KmsgrabCapture, screencast_stream
 
     cap = None
-    leds_cfg = None
+    key = None
     prev = None
     sent = 0
     t_win = time.time()
+
+    def build(cfg):
+        """Crea e avvia il backend; ritorna (cap, descrizione)."""
+        if cfg["capture"] == "kmsgrab":
+            c = KmsgrabCapture(cfg["leds"], fps=cfg["fps"], device=cfg["drm_device"]).start()
+            return c, f"kmsgrab {c.binary} su {cfg['drm_device']}"
+        node, w, h = screencast_stream()
+        c = Capture(node, cfg["leds"], fps=cfg["fps"])
+        c.start()
+        return c, f"portal node={node} sorgente {w}x{h}"
+
     while True:
         cfg = state.snapshot()
         if not cfg["running"]:
             if cap is not None:
                 cap.stop()
                 cap = None
+                key = None
             prev = None
             time.sleep(0.15)
             continue
 
-        if cap is None or leds_cfg != cfg["leds"]:
+        want = (cfg["capture"], cfg["leds"], cfg["drm_device"], cfg["fps"])
+        dead = cap is not None and hasattr(cap, "alive") and not cap.alive()
+        if cap is None or want != key or dead:
             if cap is not None:
+                err = cap.error_text() if hasattr(cap, "error_text") else ""
                 cap.stop()
+                cap = None
+                if dead:
+                    with state.lock:
+                        state.stream_error = f"kmsgrab terminato: {err}"[:300]
+                    log("kmsgrab terminato:", err)
+                    time.sleep(3)
+                    continue
             try:
-                node, w, h = screencast_stream()
-                cap = Capture(node, cfg["leds"], fps=cfg["fps"])
-                cap.start()
-                leds_cfg = cfg["leds"]
-                log(f"cattura avviata: node={node} sorgente {w}x{h} led={cfg['leds']}")
+                cap, desc = build(cfg)
+                key = want
+                log(f"cattura avviata ({cfg['capture']}): {desc} led={cfg['leds']}")
                 with state.lock:
                     state.stream_error = ""
                     state.last_error = ""
@@ -231,9 +254,8 @@ def capture_loop(state, strip):
             time.sleep(0.005)
             continue
 
-        rows = max(1, int(round(cap.gh * cfg["band"])))
         gh, gw = frame.shape[0], frame.shape[1]
-        rows = min(rows, gh)
+        rows = min(max(1, int(round(gh * cfg["band"]))), gh)
         band = frame[:rows] if cfg["side"] == "top" else frame[gh - rows:]
         sub = gw // cfg["leds"]
         if sub < 1:
@@ -358,7 +380,7 @@ class DBusService:
             value = bool(value)
         elif key == "leds":
             value = max(1, min(256, int(value)))
-        elif key in ("port", "side", "baud", "fps"):
+        elif key in ("port", "side", "baud", "fps", "capture", "drm_device"):
             value = type(DEFAULTS[key])(value)
         else:
             return False, f"parametro sconosciuto: {key}"