Render: Gracefully handle systems without JACK, show error dialog

src/jacklib.py

@@ -30,6 +30,7 @@ try:
         jacklib = cdll.LoadLibrary("libjack.so.0")
 except:
     jacklib = None
+    raise ImportError("JACK not available in this system")
 
 # JACK2 test
 try:

src/jacklib_helpers.py

@@ -16,7 +16,10 @@
 #
 # For a full copy of the GNU General Public License see the COPYING file
 
-import jacklib
+try:
+    import jacklib
+except ImportError:
+    jacklib = None
 
 def get_jack_status_error_string(c_status):
     status = c_status.value

src/render.py

@@ -305,6 +305,11 @@ if __name__ == '__main__':
     app.setOrganizationName("Cadence")
     app.setWindowIcon(QIcon(":/scalable/cadence.svg"))
 
+    if not jacklib:
+        QMessageBox.critical(None, app.translate("RenderW", "Error"), app.translate("RenderW",
+            "JACK is not available in this system, cannot use this application."))
+        sys.exit(1)
+
     for iPATH in PATH:
         if os.path.exists(os.path.join(iPATH, "jack_capture")):
             break
@@ -312,7 +317,7 @@ if __name__ == '__main__':
         QMessageBox.critical(None, app.translate("RenderW", "Error"), app.translate("RenderW",
             "The 'jack_capture' application is not available.\n"
             "Is not possible to render without it!"))
-        sys.exit(1)
+        sys.exit(2)
 
     jackStatus = jacklib.jack_status_t(0)
     jackClient = jacklib.client_open("Render", jacklib.JackNoStartServer, jacklib.pointer(jackStatus))