sync image after change:
  XClearWindow(xw->display,xw->window);
    XSync(xw->display,FALSE);  /* act as XFlush and wait for all requests to
be
                                  received and processed by the X server */
make XSHM stuff thread safe?
error handling http://tronche.com/gui/x/xlib/event-handling/protocol-errors/default-handlers.html
XVisualInfo
http://nobug.ifrance.com/nobug2/article1/babyloon/tut_xwin.htm