Add XOSC Viewer, use this as destination for xform

src/osn-viewer.lisp

@@ -103,6 +103,9 @@
       ((:menu 
         (("OSN File" 
           :callback 'application-interface-new-osn
+          :callback-type :interface)
+         ("XOSC File" 
+          :callback 'application-interface-new-xosc
           :callback-type :interface))
         :title "New")
        ("Open ..."
@@ -184,15 +187,8 @@
 (defmethod export-osn-to-xosc ((viewer osn-viewer))
   (let ((osn (first (capi:graph-pane-roots (slot-value viewer 'osn-graph-pane)))))
     (when osn
-      (multiple-value-bind (pathname ok)
-          (capi:prompt-for-file "Export OSN To XOSC"
-                                :operation :save
-                                :filters '("XOSC Files" "*.XOSC")
-                                :filter "*.XOSC")
-        (when ok
-          (capi:with-busy-interface (viewer)
-            (with-open-file (stream pathname #+(or) (ensure-pathname-type pathname "xosc")
-                                    :external-format :utf-8
-                                    :element-type :default
-                                    :direction :output :if-exists :supersede)
-              (osn-os10:write-os10-stream osn stream))))))))
+      (application-interface-new-xosc
+       viewer
+       :content
+       (with-output-to-string (stream)
+         (osn-os10:write-os10-stream osn stream))))))