Your application might require the ability to set the clip region to the intersection of the current clip region and another region. Do this with GpiIntersectClipRectangle, as shown in the following:

#include <os2.h>
void fncCLIP05(void){
    RECTL rcl;
    HPS hps;
        .
        . /* Load rcl with coordinates of rectangle to intersect. */
        .
    GpiIntersectClipRectangle(hps, &rcl);
} /* fncCLIP05 */