wayland: prefer subsurface when possible

Quite a few applications use GTK_WINDOW_POPUP to create various
temporary windows and place then on screen. That works fine on X11 but
on Wayland there is no global coordinate system for regular surfaces.

If the application is using a gdk temp window and set a parent with
gtk_window_transient_for(), the gdk wayland backend has all it needs to
create a subsurface that can be placed at will by the application.

Bugzilla: https://bugzilla.gnome.org/show_bug.cgi?id=759738

2 files changed, 69 insertions, 0 deletions

diff --git a/tests/Makefile.am b/tests/Makefile.am
index f2123d97db..85d06bae6c 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -170,6 +170,7 @@ noinst_PROGRAMS =  $(TEST_PROGS)	\
 	gdkgears			\
 	listmodel			\
 	foreigndrawing			\
+	testpopup			\
 	$(NULL)
 
 if USE_X11
diff --git a/tests/testpopup.c b/tests/testpopup.c
new file mode 100644
index 0000000000..cd82468c49
--- /dev/null
+++ b/tests/testpopup.c
@@ -0,0 +1,68 @@
+#include <gtk/gtk.h>
+
+static gboolean
+draw_popup (GtkWidget *widget,
+            cairo_t   *cr,
+            gpointer   data)
+{
+  cairo_set_source_rgb (cr, 1, 0, 0);
+  cairo_paint (cr);
+
+  return FALSE;
+}
+
+static gboolean
+place_popup (GtkWidget *parent,
+             GdkEvent  *event,
+             GtkWidget *popup)
+{
+  GdkEventMotion *ev_motion = (GdkEventMotion *) event;
+  gint width, height;
+
+  gtk_window_get_size (GTK_WINDOW (popup), &width, &height);
+  gtk_window_move (GTK_WINDOW (popup),
+                   (int) ev_motion->x_root - width / 2,
+                   (int) ev_motion->y_root - height / 2);
+
+  return FALSE;
+}
+
+static gboolean
+on_map_event (GtkWidget *parent,
+              GdkEvent  *event,
+              gpointer   data)
+{
+  GtkWidget *popup;
+
+  popup = gtk_window_new (GTK_WINDOW_POPUP);
+
+  gtk_widget_set_size_request (GTK_WIDGET (popup), 20, 20);
+  gtk_widget_set_app_paintable (GTK_WIDGET (popup), TRUE);
+  gtk_window_set_transient_for (GTK_WINDOW (popup), GTK_WINDOW (parent));
+  g_signal_connect (popup, "draw", G_CALLBACK (draw_popup), NULL);
+  g_signal_connect (parent, "motion-notify-event", G_CALLBACK (place_popup), popup);
+
+  gtk_widget_show (popup);
+
+  return FALSE;
+}
+
+int
+main (int argc, char *argv[])
+{
+  GtkWidget *window;
+
+  gtk_init (&argc, &argv);
+
+  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+
+  gtk_widget_set_events (window, GDK_POINTER_MOTION_MASK);
+  g_signal_connect (window, "destroy", gtk_main_quit, NULL);
+  g_signal_connect (window, "map-event", G_CALLBACK (on_map_event), NULL);
+
+  gtk_widget_show (window);
+
+  gtk_main ();
+
+  return 0;
+}