Preview: fallback webcam quand le DSLR ne supporte pas le live view

Le Canon 6D ne supporte pas capture_preview() via gphoto2.
Utilise la webcam embarquee pour le preview tout en gardant le DSLR pour la capture.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/camera.py

@@ -63,6 +63,7 @@ class Camera:
         self.mode = "simulation"  # "gphoto2", "webcam", "simulation"
         self.webcam = None
         self.webcam_index = -1
+        self._preview_webcam_fallback = None
 
     def connecter(self, source=None) -> bool:
         """Connecte la camera. source: 'gphoto2', 'webcam:0', 'webcam:2', etc."""
@@ -113,6 +114,9 @@ class Camera:
 
     def deconnecter(self):
         """Deconnecte l'appareil photo."""
+        if self._preview_webcam_fallback:
+            self._preview_webcam_fallback.release()
+            self._preview_webcam_fallback = None
         if self.camera and GPHOTO2_DISPONIBLE:
             try:
                 self.camera.exit()
@@ -196,10 +200,34 @@ class Camera:
         if self.mode == "webcam":
             return self._preview_webcam()
         elif self.mode == "gphoto2":
-            return self._preview_gphoto2()
+            data = self._preview_gphoto2()
+            if data:
+                return data
+            # Fallback webcam pour le preview si le DSLR ne supporte pas le live view
+            if not self._preview_webcam_fallback:
+                self._init_preview_fallback()
+            if self._preview_webcam_fallback:
+                ret, frame = self._preview_webcam_fallback.read()
+                if ret:
+                    _, buf = cv2.imencode(".jpg", frame, [cv2.IMWRITE_JPEG_QUALITY, 70])
+                    return buf.tobytes()
+            return self._preview_simulation()
         else:
             return self._preview_simulation()
 
+    def _init_preview_fallback(self):
+        """Ouvre une webcam pour le preview quand le DSLR ne supporte pas le live view."""
+        webcams = lister_webcams()
+        for wc in webcams:
+            cap = cv2.VideoCapture(wc["index"])
+            if cap.isOpened():
+                cap.set(cv2.CAP_PROP_FRAME_WIDTH, 1280)
+                cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 720)
+                self._preview_webcam_fallback = cap
+                log.info(f"Preview fallback webcam : {wc['nom']}")
+                return
+        log.warning("Aucune webcam disponible pour le preview fallback")
+
     def _preview_gphoto2(self) -> bytes | None:
         try:
             fichier = self.camera.capture_preview()