XtRegisterDrawable - register a drawable with the Intrinsics event dispatcher
#include <X11/Intrinsic.h>
void XtRegisterDrawable(Display* display, Drawable
    drawable, Widget widget);
void XtUnregisterDrawable(Display* display, Drawable
    drawable);
  - display
- Specifies the drawable's display.
- drawable
- Specifies the drawable to register.
- widget
- Specifies the widget to register the drawable for.
XtRegisterDrawable associates the specified drawable with the specified
  widget so that future calls to XtWindowToWidget with the drawable will
  return the widget. The default event dispatcher will dispatch future core
  events that arrive with the drawable to the widget as though the event
  contained the widget's window, but the event itself will not be changed in any
  way when being passed to even handler or action procedures.If the drawable is already registered with another widget, or if
    the drawable is the window of a widget in the client's widget tree, the
    results of calling XtRegisterDrawable are undefined.
XtUnregisterDrawable removes an association created with
    XtRegisterDrawable. If the drawable is the window of a widget in the
    client's widget tree the results of calling XtUnregisterDrawable are
    undefined.
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface