gtk: equalize on double clicking the split handle

src/apprt/gtk/Split.zig

@@ -111,6 +111,16 @@ pub fn init(
     // Keep a long-lived reference, which we unref in destroy.
     _ = c.g_object_ref(paned);
 
+    // Clicks
+    const gesture_click = c.gtk_gesture_click_new();
+    errdefer c.g_object_unref(gesture_click);
+    c.gtk_event_controller_set_propagation_phase(@ptrCast(gesture_click), c.GTK_PHASE_CAPTURE);
+    c.gtk_gesture_single_set_button(@ptrCast(gesture_click), 1);
+    c.gtk_widget_add_controller(paned, @ptrCast(gesture_click));
+
+    // Signals
+    _ = c.g_signal_connect_data(gesture_click, "pressed", c.G_CALLBACK(&gtkMouseDown), self, null, c.G_CONNECT_DEFAULT);
+
     // Update all of our containers to point to the right place.
     // The split has to point to where the sibling pointed to because
     // we're inheriting its parent. The sibling points to its location
@@ -236,6 +246,19 @@ pub fn equalize(self: *Split) f64 {
     return weight;
 }
 
+fn gtkMouseDown(
+    _: *c.GtkGestureClick,
+    n_press: c.gint,
+    _: c.gdouble,
+    _: c.gdouble,
+    ud: ?*anyopaque,
+) callconv(.C) void {
+    if (n_press == 2) {
+        const self: *Split = @ptrCast(@alignCast(ud));
+        _ = equalize(self);
+    }
+}
+
 // maxPosition returns the maximum position of the GtkPaned, which is the
 // "max-position" attribute.
 fn maxPosition(self: *Split) f64 {