XtAddExposureToRegion - merge exposure events into a region
#include <X11/Intrinsic.h>
void XtAddExposureToRegion(XEvent *event, Region
    region);
  - event
- Specifies a pointer to the Expose or GraphicsExpose
    event.
- region
- Specifies the region object (as defined in
    <X11/Xutil.h>).
The XtAddExposureToRegion function computes the union of the rectangle
  defined by the exposure event and the specified region. Then, it stores the
  results back in region. If the event argument is not an Expose or
  GraphicsExpose event, XtAddExposureToRegion returns without an
  error and without modifying region.This function is used by the exposure compression mechanism (see
    Section 7.9.3).
X Toolkit Intrinsics - C Language Interface
Xlib - C Language X Interface