Add a test app

This app has a dynamic cursor that is the GTK logo, loaded from
an SVG to make it come out at the nominal size of the cursor
theme, while taking fractional scaling into account.

tests/callbackcursor.c

@@ -0,0 +1,98 @@
+/* testpaintablecursor.c
+ * Copyright (C) 2024 Red Hat, Inc.
+ * Author: Matthias Clasen
+ *
+ * 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 <gtk/gtk.h>
+
+static GdkTexture *
+cursor_callback (GdkCursor *cursor,
+                 int        cursor_size,
+                 double     scale,
+                 int       *width,
+                 int       *height,
+                 int       *hotspot_x,
+                 int       *hotspot_y,
+                 gpointer   data)
+{
+  GdkPixbuf *pixbuf;
+  GdkTexture *texture;
+  GError *error = NULL;
+  int scaled_size;
+
+  scaled_size = ceil (cursor_size * scale);
+
+  g_print ("cursor size %d scale %g\n", cursor_size, scale);
+  g_print ("resulting pixels %d x %d\n", scaled_size, scaled_size);
+
+  pixbuf = gdk_pixbuf_new_from_file_at_size ((const char *)data,
+                                             scaled_size, scaled_size,
+                                             &error);
+  if (!pixbuf)
+    {
+      g_print ("%s\n", error->message);
+      g_error_free (error);
+      return NULL;
+    }
+
+  texture = gdk_texture_new_for_pixbuf (pixbuf);
+
+  g_object_unref (pixbuf);
+
+  *width = cursor_size;
+  *height = cursor_size;
+  *hotspot_x = 0;
+  *hotspot_y = 0;
+
+  return texture;
+}
+
+int
+main (int argc, char *argv[])
+{
+  GtkWidget *window, *button;
+  gboolean done = FALSE;
+  GdkCursor *cursor;
+
+  gtk_init ();
+
+  window = gtk_window_new ();
+  gtk_window_set_title (GTK_WINDOW (window), "hello world");
+  gtk_window_set_resizable (GTK_WINDOW (window), FALSE);
+
+  button = gtk_button_new ();
+  gtk_button_set_label (GTK_BUTTON (button), "hello world");
+  gtk_widget_set_margin_top (button, 10);
+  gtk_widget_set_margin_bottom (button, 10);
+  gtk_widget_set_margin_start (button, 10);
+  gtk_widget_set_margin_end (button, 10);
+
+  cursor = gdk_cursor_new_from_callback (cursor_callback,
+                                         (gpointer) "docs/reference/gsk/gtk-logo.svg", NULL,
+                                         gdk_cursor_new_from_name ("default", NULL));
+
+  gtk_widget_set_cursor (button, cursor);
+  g_object_unref (cursor);
+
+  gtk_window_set_child (GTK_WINDOW (window), button);
+
+  gtk_window_present (GTK_WINDOW (window));
+
+  while (!done)
+    g_main_context_iteration (NULL, TRUE);
+
+  return 0;
+}

tests/meson.build

@@ -1,5 +1,6 @@
 gtk_tests = [
   # testname, optional extra sources
+  ['callbackcursor'],
   ['devicepixels'],
   ['testsections'],
   ['testfilelauncher'],