feat(entry): implement def _detect_backend_from_qpa_env

scanslicer/entry.py

@@ -21,3 +21,18 @@ def parse_args(argv=None):
         help="Display backend selection (default: auto)",
     )
     return parser.parse_args(argv)
+
+
+# _detect_backend_from_qpa_env: function definition for ScanSlicer behavior.
+def _detect_backend_from_qpa_env():
+    qpa_value = os.environ.get("QT_QPA_PLATFORM", "").strip().lower()
+    if not qpa_value:
+        return None
+
+    tokens = [token.strip() for token in qpa_value.split(";") if token.strip()]
+    for token in tokens:
+        if token == "wayland":
+            return "wayland"
+        if token in ("xcb", "x11"):
+            return "x11"
+    return None