smnb

saved_proc = (WNDPROC)GetWindowLong(hwnd, GWL_WNDPROC);
SetWindowLong(hwnd, GWL_WNDPROC, (LONG)new_proc);

LRESULT CALLBACK new_proc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam){
    PAINTSTRUCT ps;
    HDC hdc;

    switch(message)    {
        case WM_PAINT:
            hdc = BeginPaint(hwnd, &ps);
            OnPaint(hwnd, hdc, NULL);
            EndPaint(hwnd, &ps);
            return 0;
        default:
            break;   
    }
    return CallWindowProc(saved_proc, hwnd, message, wParam, lParam);
}

EXECUTION_STATE esFlags

HDC hdc_mem; // memory device context
HBITMAP hbitmap; // actual memory to draw
:
void prepare_img(){
    HDC hDC = GetDC(hWnd);
    hdc_mem = CreateCompatibleDC(hDC); // or use NULL for screen DC
    
    RECT rt;
    GetClientRect(hWnd, &rt);
    
    hbitmap = CreateCompatibleBitmap( hDC, rt.right, rt.bottom );
    SelectObject(hdc_mem,hbitmap); // assign memory to dc
    HBRUSH hOrigBrush = (HBRUSH)SelectObject( full_range_dc, GetStockObject( BLACK_BRUSH ) );
    PatBlt( hdc_mem, 0, 0, rt.right, rt.bottom, PATCOPY ); // paint back in black
    {
       // Draw Something to thie hdc_mem
       // TextOut(hdc_mem , 10 , 10 , "Hello" , 5);
    }
    ReleaseDC(hWnd , hDC);
}
void un_prepare(){
    DeleteDC(hdc_mem); hdc_mem=NULL;
    DeleteObject(hbitmap); hbitmap=NULL;
}
:
// in Paint Handler
BitBlt( hdc, 0, 0, rt.right, rt.Widtg, hdc_mem, 0, 0, SRCCOPY );