Emit "link-toggled" signal when two ports widgets are connected

src/view/port.rs

@@ -1,10 +1,16 @@
-use gtk::{glib, prelude::*, subclass::prelude::*};
+use gtk::{
+    gdk,
+    glib::{self, subclass::Signal},
+    prelude::*,
+    subclass::prelude::*,
+};
+use log::warn;
 use pipewire::spa::Direction;
 
 use crate::controller::MediaType;
 
 mod imp {
-    use once_cell::unsync::OnceCell;
+    use once_cell::{sync::Lazy, unsync::OnceCell};
     use pipewire::spa::Direction;
 
     use super::*;
@@ -23,7 +29,22 @@ mod imp {
         type ParentType = gtk::Button;
     }
 
-    impl ObjectImpl for Port {}
+    impl ObjectImpl for Port {
+        fn signals() -> &'static [Signal] {
+            static SIGNALS: Lazy<Vec<Signal>> = Lazy::new(|| {
+                vec![Signal::builder(
+                    "port-toggled",
+                    // Provide id of output port and input port to signal handler.
+                    &[<u32>::static_type().into(), <u32>::static_type().into()],
+                    // signal handler sends back nothing.
+                    <()>::static_type().into(),
+                )
+                .build()]
+            });
+
+            SIGNALS.as_ref()
+        }
+    }
     impl WidgetImpl for Port {}
     impl ButtonImpl for Port {}
 }
@@ -46,6 +67,44 @@ impl Port {
 
         res.set_child(Some(&gtk::Label::new(Some(name))));
 
+        // Add either a drag source or drop target controller depending on direction,
+        // they will be responsible for link creation by dragging an output port onto an input port.
+        //
+        // FIXME: The type used for dragging is simply a u32.
+        //   This means that anything that provides a u32 could be dragged onto a input port,
+        //   leading to that port trying to create a link to an invalid output port.
+        //   We should use a newtype instead of a plain u32.
+        //   Additionally, this does not protect against e.g. dropping an outgoing audio port on an ingoing video port.
+        match direction {
+            Direction::Input => {
+                let drop_target = gtk::DropTarget::new(u32::static_type(), gdk::DragAction::COPY);
+                let this = res.clone();
+                drop_target.connect_drop(move |drop_target, val, _, _| {
+                    if let Some(source_id) = val.downcast_ref::<u32>() {
+                        // Get the callback registered in the widget and call it
+                        let source_id = source_id.get_some();
+                        drop_target
+                            .get_widget()
+                            .expect("Drop target has no widget")
+                            .emit_by_name("port-toggled", &[&source_id, &this.id()])
+                            .expect("Failed to send signal");
+                    } else {
+                        warn!("Invalid type dropped on ingoing port");
+                    }
+
+                    true
+                });
+                res.add_controller(&drop_target);
+            }
+            Direction::Output => {
+                // The port will simply provide its pipewire id to the drag target.
+                let drag_src = gtk::DragSourceBuilder::new()
+                    .content(&gdk::ContentProvider::new_for_value(&(id.to_value())))
+                    .build();
+                res.add_controller(&drag_src);
+            }
+        }
+
         // Color the port according to its media type.
         match media_type {
             Some(MediaType::Video) => res.add_css_class("video"),
@@ -57,6 +116,11 @@ impl Port {
         res
     }
 
+    pub fn id(&self) -> u32 {
+        let private = imp::Port::from_instance(self);
+        private.id.get().copied().expect("Port id is not set")
+    }
+
     pub fn direction(&self) -> &Direction {
         let private = imp::Port::from_instance(self);
         private.direction.get().expect("Port direction is not set")