Created attachment 341038 [details]
VNC Client

A simple Python2 VNC client (Gtk2) script connects a VNC server sending a dummy cursor (hotx=5, hoty=10, width=1 and height=1). It produces a warning but does not crash and the application is fully working a excepted.

Warning:

./vncviewer.py:11: GtkWarning: IA__gdk_cursor_new_from_pixbuf: assertion '0 <= x && x < gdk_pixbuf_get_width (pixbuf)' failed
  gtk.main()

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The same script ported to Python3 (Gtk3) don't produce any warning as excepted but crash and is unusable.

Error:

(vncviewer.py3:1487): Gdk-ERROR **: The program 'vncviewer.py3' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadMatch (invalid parameter attributes)'.
  (Details: serial 276 error_code 8 request_code 139 (RENDER) minor_code 27)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the GDK_SYNCHRONIZE environment
   variable to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

+ Trace 236906

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This patch fix the problem:

diff --git a/src/vnccursor.c b/src/vnccursor.c
index 4dd188f..5cc343b 100644
--- a/src/vnccursor.c
+++ b/src/vnccursor.c
@@ -143,6 +143,9 @@ VncCursor *vnc_cursor_new(guint8 *data,
                           guint16 hotx, guint16 hoty,
                           guint16 width, guint16 height)
 {
+    /* Clamp hotx and hoty */
+    if(hotx > width) hotx = width;
+    if(hoty > height) hoty = height;
     return VNC_CURSOR(g_object_new(VNC_TYPE_CURSOR,
                                    "data", data,
                                    "hotx", hotx,


This is probably a faulty behaviour of the VNC Server (Red Hat 3 Update 9 Xvnc 4.0b4). But I think this error should be catch at least in the GtkVnc lib (To be able to connects all VNC Server).

Thanks you.