XtTranslateCoords - translate widget coordinates
#include <X11/Intrinsic.h>
void XtTranslateCoords(Widget w, Position x, Position y, Position *rootx_return, Position *rooty_return);
Returns the root-relative x and y coordinates.
Specify the widget-relative x and y coordinates.
Specifies the widget.
While XtTranslateCoords is similar to the Xlib XTranslateCoordinates function, it does not generate a server request because all the required information already is in the widget's data structures.
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface