This function indicates that drawing is about to take place after a palette has been selected.

#define INCL_WIN /* Or use INCL_PM, */
#include <os2.h>

HWND      hwnd;      /*  Window handle where drawing is taking place. */
HPS       hps;       /*  Presentation-space handle. */
PULONG    pcclr;     /*  Number of physical palette entries changed. */
LONG      lChanged;  /*  Number of colors remapped. */

lChanged = WinRealizePalette(hwnd, hps, pcclr);