Make Nodes on graph draggable

Cargo.lock

@@ -331,6 +331,7 @@ name = "graphui-rs"
 version = "0.0.1"
 dependencies = [
  "cairo-rs",
+ "gdk",
  "gio",
  "glib",
  "gtk",

Cargo.toml

@@ -9,5 +9,6 @@ edition = "2018"
 [dependencies]
 cairo-rs = "0.9.1"
 glib = "0.10.3"
+gdk = "0.13.2"
 gtk = "0.9.2"
 gio = "0.9.1"

src/view/pipewire_node.rs

@@ -1,26 +1,63 @@
-use gtk::GridExt;
-
+use gtk::prelude::*;
+use gdk::prelude::*;
 use std::collections::HashMap;
 
 pub struct PipewireNode {
     pub(super) widget: gtk::Grid,
-    _label: gtk::Label,
+    label: gtk::Label,
+    label_box: gtk::EventBox,
     ingoing_ports: HashMap<u32, gtk::Button>,
     outgoing_ports: HashMap<u32, gtk::Button>,
 }
 
 impl PipewireNode {
     pub fn new(name: &str) -> Self {
-        let widget = gtk::Grid::new();
-        let label = gtk::Label::new(Some(name));
-        widget.attach(&label, 0, 0, 2, 1);
-
-        Self {
-            widget,
-            _label: label,
+        let result = Self {
+            widget: gtk::Grid::new(),
+            label: gtk::Label::new(Some(name)),
+            label_box: gtk::EventBox::new(),
             ingoing_ports: HashMap::new(),
             outgoing_ports: HashMap::new(),
-        }
+        };
+
+        result.label_box.add(&result.label);
+        result.widget.attach(&result.label_box, 0, 0, 2, 1);
+
+        result
+            .label_box
+            .add_events(gdk::EventMask::BUTTON1_MOTION_MASK);
+        result
+            .label_box
+            .connect_motion_notify_event(|label, event| {
+                let grid = label
+                    .get_ancestor(gtk::Grid::static_type())
+                    .unwrap()
+                    .dynamic_cast::<gtk::Grid>()
+                    .unwrap();
+                let graphview = grid
+                    .get_ancestor(gtk::Layout::static_type())
+                    .unwrap()
+                    .dynamic_cast::<gtk::Layout>()
+                    .unwrap();
+
+                // Use root coordinates to prevent jumping around
+                // as moving the widget also influences the relative coordinates.
+                let (x, y) = event.get_root();
+                let (offset_x, offset_y) = graphview.get_window().unwrap().get_root_origin();
+
+                // TODO: Calculate proper values to center the mouse on the label
+                // instead of using hardcoded offsets.
+                graphview.set_child_x(&grid, x as i32 - offset_x - 100);
+                graphview.set_child_y(&grid, y as i32 - offset_y - 50);
+
+                // FIXME: If links become proper widgets,
+                // we don't need to redraw the full graph everytime.
+                graphview.queue_draw();
+
+                Inhibit(true)
+            });
+
+        result
     }
 
     pub fn add_ingoing_port(&mut self, id: u32, port: gtk::Button) {