Add a simple testcase for transforms

This can help in tracking various things down,
from picking to clipping.

tests/meson.build

@@ -1,5 +1,6 @@
 gtk_tests = [
   # testname, optional extra sources
+  ['testtransform'],
   ['testdropdown'],
   ['rendernode'],
   ['rendernode-create-tests'],

tests/testtransform.c

@@ -0,0 +1,77 @@
+
+/* This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ */
+#include "config.h"
+#include <gtk/gtk.h>
+
+static void
+hello (GtkButton *button)
+{
+  g_print ("Hello!\n");
+}
+
+static void
+quit_cb (GtkWidget *widget,
+         gpointer   data)
+{
+  gboolean *done = data;
+
+  *done = TRUE;
+
+  g_main_context_wakeup (NULL);
+}
+
+int
+main (int argc, char *argv[])
+{
+  GtkWidget *window, *fixed, *button;
+  gboolean done = FALSE;
+  GskTransform *transform;
+
+  gtk_init ();
+
+  window = gtk_window_new ();
+  gtk_window_set_title (GTK_WINDOW (window), "hello world");
+  g_signal_connect (window, "destroy", G_CALLBACK (quit_cb), &done);
+
+  fixed = gtk_fixed_new ();
+  gtk_widget_set_halign (fixed, GTK_ALIGN_FILL);
+  gtk_widget_set_valign (fixed, GTK_ALIGN_FILL);
+  gtk_widget_set_hexpand (fixed, TRUE);
+  gtk_widget_set_vexpand (fixed, TRUE);
+
+  button = gtk_button_new ();
+  gtk_button_set_label (GTK_BUTTON (button), "Hello world");
+  //gtk_widget_set_size_request (button, 50, 50);
+  g_signal_connect (button, "clicked", G_CALLBACK (hello), NULL);
+
+  gtk_fixed_put (GTK_FIXED (fixed), button, 0, 0);
+
+  transform = NULL;
+  transform = gsk_transform_translate_3d (transform, &GRAPHENE_POINT3D_INIT (0, 0, 50));
+  transform = gsk_transform_perspective (transform, 170);
+  transform = gsk_transform_translate_3d (transform, &GRAPHENE_POINT3D_INIT (50, 0, 50));
+  transform = gsk_transform_rotate (transform, 30);
+  transform = gsk_transform_rotate_3d (transform, 30, graphene_vec3_y_axis ());
+  gtk_fixed_set_child_transform (GTK_FIXED (fixed), button, transform);
+
+  gtk_window_set_child (GTK_WINDOW (window), fixed);
+
+  gtk_widget_show (window);
+
+  while (!done)
+    g_main_context_iteration (NULL, TRUE);
+
+  return 0;
+}