HWND hwnd = THE_HWND;
RECT size;
GetClientRect(hwnd, &size);
int w = size.right - size.left;
int h = size.bottom - size.top;
HDC hDC = GetDC(hwnd);
HDC hMemDC = CreateCompatibleDC(hDC);
HBITMAP bmp = CreateCompatibleBitmap(hDC, w, h);
if (bmp) {
HDC hOld = (HDC)SelectObject(hMemDC, bmp);
BitBlt(hMemDC, 0, 0, w, h, hDC, 0, 0, SRCCOPY);
SelectObject(hMemDC, hOld);
DeleteDC(hMemDC);
ReleaseDC(hwnd, hDC);
}