Add an option to auto-connect JACK ports

alc/backends/jack.cpp

@@ -384,15 +384,17 @@ void JackPlayback::start()
     if(jack_activate(mClient))
         throw al::backend_exception{ALC_INVALID_DEVICE, "Failed to activate client"};
 
-    const char **ports{jack_get_ports(mClient, nullptr, nullptr,
-        JackPortIsPhysical|JackPortIsInput)};
-    if(ports == nullptr)
+    const char *devname{mDevice->DeviceName.c_str()};
+    if(ConfigValueBool(devname, "jack", "connect-ports").value_or(true))
     {
-        jack_deactivate(mClient);
-        throw al::backend_exception{ALC_INVALID_DEVICE, "No physical playback ports found"};
-    }
-    std::mismatch(mPort.begin(), mPort.end(), ports,
-        [this](const jack_port_t *port, const char *pname) -> bool
+        const char **ports{jack_get_ports(mClient, nullptr, nullptr,
+            JackPortIsPhysical|JackPortIsInput)};
+        if(ports == nullptr)
+        {
+            jack_deactivate(mClient);
+            throw al::backend_exception{ALC_INVALID_DEVICE, "No physical playback ports found"};
+        }
+        auto connect_port = [this](const jack_port_t *port, const char *pname) -> bool
         {
             if(!port) return false;
             if(!pname)
@@ -404,8 +406,10 @@ void JackPlayback::start()
                 ERR("Failed to connect output port \"%s\" to \"%s\"\n", jack_port_name(port),
                     pname);
             return true;
-        });
-    jack_free(ports);
+        };
+        std::mismatch(mPort.begin(), mPort.end(), ports, connect_port);
+        jack_free(ports);
+    }
 
     /* Reconfigure buffer metrics in case the server changed it since the reset
      * (it won't change again after jack_activate), then allocate the ring
@@ -415,7 +419,6 @@ void JackPlayback::start()
     mDevice->UpdateSize = jack_get_buffer_size(mClient);
     mDevice->BufferSize = mDevice->UpdateSize * 2;
 
-    const char *devname{mDevice->DeviceName.c_str()};
     ALuint bufsize{ConfigValueUInt(devname, "jack", "buffer-size").value_or(mDevice->UpdateSize)};
     bufsize = maxu(NextPowerOf2(bufsize), mDevice->UpdateSize);
     mDevice->BufferSize = bufsize + mDevice->UpdateSize;

alsoftrc.sample

@@ -469,6 +469,12 @@
 #  backend, opening devices, etc).
 #spawn-server = false
 
+## connect-ports:
+#  Attempts to automatically connect the client ports to physical server ports.
+#  Client ports that fail to connect will leave the remaining channels
+#  unconnected and silent (the device format won't change to accommodate).
+#connect-ports = true
+
 ## buffer-size:
 #  Sets the update buffer size, in samples, that the backend will keep buffered
 #  to handle the server's real-time processing requests. This value must be a