To receive ResizeRequest events, set the ResizeRedirect bit in the event-mask attribute of the window. Any attempts to change the size by other clients are then redirected.
The structure for this event type contains:
typedef struct {
int type; /* ResizeRequest */
unsigned long serial; /* # of last request processed by server */
Bool send_event; /* true if this came from a SendEvent request */
Display *display; /* Display the event was read from */
Window window;
int width, height;
} XResizeRequestEvent;
The window member is set to the window whose size another client attempted to change. The width and height members are set to the inside size of the window, excluding the border.