Отрисовка на многослойном окне

HBITMAP hbmp;
 
Form1->BorderStyle = bsNone;
     
SetWindowLong(Form1->Handle, GWL_EXSTYLE,GetWindowLong(Form1->Handle,GWL_EXSTYLE) ^ WS_EX_LAYERED);
    
UnicodeString img_file = "d:/BGimage.png";
 
Gdiplus::Bitmap *img = new Gdiplus::Bitmap(img_file.w_str(), true);
 
GetHBITMAP(0,&hbmp)==Gdiplus::Ok)
 
Form1->Width = img->GetWidth();
Form1->Height = img->GetHeight();
delete img;
 
GetDC(NULL);
HDC screendc = NULL;
HDC backdc = CreateCompatibleDC(screendc);
 
SelectObject(backdc,hbmp);
pt1 = Point(Form1->Left, Form1->Top);
pt2 = Point(0,0);
sz.cx = Form1->Width;
sz.cy = Form1->Height;
 
TBlendFunction bf;
bf.BlendOp = AC_SRC_OVER;
bf.BlendFlags =   0;
bf.SourceConstantAlpha = 0xff;
bf.AlphaFormat = AC_SRC_ALPHA;
 
UpdateLayeredWindow(Handle,screendc, &pt1,&sz,backdc,&pt2,0,&bf,ULW_ALPHA);

Form1->PaintControls(backdc,0);
//и обновляем окно
UpdateLayeredWindow(/*с ранее указанными параметрами*/);

Image1->Picture = NULL;
Form1->PaintControls(backdc,0);
UpdateLayeredWindow(/*с ранее указанными параметрами*/);

HDC old_dc = backdc;

backdc = old_dc;
UpdateLayeredWindow(/*с ранее указанными параметрами*/);