This function opens a device context for a window.

#define INCL_WINWINDOWMGR /* Or use INCL_WIN, INCL_PM, Also in COMMON section */
#include <os2.h>

HWND    hwnd;  /*  Window handle. */
HDC     hdc;   /*  Device-context handle. */

hdc = WinOpenWindowDC(hwnd);