procedure TForm1.Button1Click(Sender: TObject);
var
FullscreenCanvas:TCanvas;
dc:HDC;
begin
DC := GetDC(GetWindow(//窗口名));
FullscreenCanvas := TCanvas.Create;
FullscreenCanvas.Handle := DC;
image1.Canvas.CopyRect(Rect(0, 0, screen.Width,screen.Height),fullscreenCanvas,Rect (0, 0, Screen.Width, Screen.Height));
FullscreenCanvas.Free;
ReleaseDC (0, DC);
end;