The following code illustrates how to change graphical data for a graphic button.

typedef struct {
   USHORT  usReserved;                  /*Reserved field */
   PSZ     pszText;                     /*Initial text of button */
   HMODULE hmod;                        /*Module handle for bit maps */
   USHORT  cBitmaps;                    /*Number of bit maps */
   USHORT  aidBitmap[1];                /*Array of bit-map IDs */
}GBTNCDATA;
typedef GBTNCDATA *PGBTNCDATA;

GBTNCDATA  cdata;

cdata.usReserved = GB_STRUCTURE;
cdata.pszText    = "Play";
cdata.hmod       = hmodBitmaps;
cdata.cBitmaps   = 1;
cdata.aidBitmap[0] = ID_PLAY;

WinSendMsg ( hwndButton, GBM_SETGRAPHICDATA, (MPARAM)&cdata, 0L;