draft: Port 'Screencast' demo to Vala

src/Screencast/main.vala

@@ -0,0 +1,87 @@
+#! /usr/bin/env -S vala workbench.vala --pkg libadwaita-1 --pkg libportal-gtk4 --pkg gstreamer-1.0
+public errordomain MessageError {
+    FAILED;
+}
+private Gtk.Picture output;
+private Xdp.Portal portal;
+private Xdp.Parent parent;
+
+async void start_screencast_session (Xdp.Portal portal, Xdp.Parent parent) throws Error {
+
+    Xdp.Session session = yield portal.create_screencast_session (MONITOR, // Output Type
+        NONE, // Screencast Flags
+        EMBEDDED, // Cursor Mode
+        TRANSIENT, // Persist Mode
+        null, // Restore token
+        null); // Cancellable
+
+    if (session == null) {
+        throw new MessageError.FAILED (@"Permission denied");
+    }
+
+    bool success = yield session.start (parent, null);
+
+    if (!success) {
+        throw new MessageError.FAILED (@"Could not start session");
+    }
+    int pw_remote = session.open_pipewire_remote ();
+    var pipeline = new Gst.Pipeline ("");
+    Gst.Element source = Gst.ElementFactory.make ("pipewiresrc", "source");
+    Gst.Element queue = Gst.ElementFactory.make ("queue", "queue"); // add a queue element
+    Gst.Element paintable_sink = Gst.ElementFactory.make (
+                                                          "gtk4paintablesink",
+                                                          "paintable_sink"
+    );
+    Gst.Element glsinkbin = Gst.ElementFactory.make ("glsinkbin", "glsinkbin");
+
+    // Set up and Link Pipeline
+    source.set_property ("fd", pw_remote); // pw_remote is the file descriptor obtained from libportal
+
+    // Obtain the node id from the screencast session
+    Variant streams = session.get_streams ();
+    uint node_id = streams.get_child_value (0).get_child_value (0).get_uint32 ();
+    if (node_id == 0) {
+        throw new MessageError.FAILED (@"No available node");
+    }
+
+    source.set_property ("path", node_id);
+    glsinkbin.set_property ("sink", paintable_sink);
+
+    pipeline.add (source);
+    pipeline.add (queue);
+    pipeline.add (glsinkbin);
+    source.link (queue);
+    queue.link (glsinkbin);
+
+    var paintable = Value (typeof (Gdk.Paintable));
+
+    paintable_sink.get_property ("paintable", ref paintable);
+    output.paintable = (Gdk.Paintable) paintable.get_object ();
+
+    // Start the pipeline
+    pipeline.set_state (PLAYING);
+
+    // Handle cleanup on application exit
+    output.destroy.connect (() => {
+        pipeline.set_state (NULL);
+    });
+}
+
+async void on_button_clicked () {
+    try {
+        yield start_screencast_session (portal, parent);
+    } catch (Error e) {
+        critical (@"$(e.message)");
+    }
+}
+
+public void main (string[] args) {
+    unowned string[] arguments = null;
+    Gst.init (ref arguments);
+    portal = new Xdp.Portal ();
+    parent = Xdp.parent_new_gtk (workbench.window);
+    output = (Gtk.Picture) workbench.builder.get_object ("output");
+    var button = (Gtk.Button) workbench.builder.get_object ("button");
+
+    button.clicked.connect (on_button_clicked);
+}