The following figure is an example of how to use area functions to draw two intersecting boxes, filled, using the winding mode.

#define INCL_GPI
#include <os2.h>
void fncAREA03(void){
    POINTL ptl;            /* Structure for current position */
    HPS    hps;

    GpiBeginArea(hps, BA_WINDING);
    ptl.x = 100;
    ptl.y = 50;
    GpiMove(hps, &ptl);
    ptl.x = 300;
    ptl.y = 250;
    GpiBox(hps, DRO_OUTLINE, &ptl, 0, 0);
    ptl.x = 180;
    ptl.y = 120;
    GpiMove(hps, &ptl);
    ptl.x = 380;
    ptl.y = 320;
    GpiBox(hps, DRO_OUTLINE, &ptl, 0, 0);
    GpiEndArea(hps);
} /* fncAREA03 */