1 files changed, 75 insertions, 0 deletions
diff --git a/utils/xdbe.c b/utils/xdbe.c
new file mode 100644
index 0000000..d62183e
--- /dev/null
+++ b/utils/xdbe.c
@@ -0,0 +1,75 @@
+/* xscreensaver, Copyright (c) 1998, 1999, 2006
+ *  by Jamie Zawinski <jwz@jwz.org>
+ *
+ * Permission to use, copy, modify, distribute, and sell this software and its
+ * documentation for any purpose is hereby granted without fee, provided that
+ * the above copyright notice appear in all copies and that both that
+ * copyright notice and this permission notice appear in supporting
+ * documentation.  No representations are made about the suitability of this
+ * software for any purpose.  It is provided "as is" without express or 
+ * implied warranty.
+ */
+
+/* The XDBE (Double Buffering) extension is pretty tricky to use, since you
+   can get X errors at inconvenient times during initialization.  This file
+   contains a utility routine to make it easier to deal with.
+ */
+
+#include "utils.h"
+#include "xdbe.h"
+#include "resources.h"		/* for get_string_resource() */
+
+/* #define DEBUG */
+
+#ifdef DEBUG
+# include <X11/Xmu/Error.h>
+#endif
+
+extern char *progname;
+
+#ifdef HAVE_DOUBLE_BUFFER_EXTENSION	/* whole file */
+
+static Bool xdbe_got_x_error = False;
+static int
+xdbe_ehandler (Display *dpy, XErrorEvent *error)
+{
+  xdbe_got_x_error = True;
+
+#ifdef DEBUG
+  fprintf (stderr, "\n%s: ignoring X error from DOUBLE-BUFFER:\n", progname);
+  XmuPrintDefaultErrorMessage (dpy, error, stderr);
+  fprintf (stderr, "\n");
+#endif
+
+  return 0;
+}
+
+
+XdbeBackBuffer 
+xdbe_get_backbuffer (Display *dpy, Window window,
+                     XdbeSwapAction action)
+{
+  XdbeBackBuffer b;
+  XErrorHandler old_handler;
+  int maj, min;
+
+  if (!get_boolean_resource(dpy, "useDBE", "Boolean"))
+    return 0;
+
+  if (!XdbeQueryExtension (dpy, &maj, &min))
+    return 0;
+
+  XSync (dpy, False);
+  xdbe_got_x_error = False;
+  old_handler = XSetErrorHandler (xdbe_ehandler);
+  b = XdbeAllocateBackBufferName(dpy, window, XdbeUndefined);
+  XSync (dpy, False);
+  XSetErrorHandler (old_handler);
+
+  if (xdbe_got_x_error)
+    return 0;
+
+  return b;
+}
+
+#endif /* HAVE_DOUBLE_BUFFER_EXTENSION */