2,用如下代码
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procedure TForm1.Button1Click(Sender: TObject);
var
r:thandle;
i:integer;
begin
for i:=1 to trunc(width/1.414) do
begin
r:=CreateEllipticRgn(trunc(width/2)-i,trunc(height/2)-i,trunc(width/2)+i,trunc(height/2)+i);
SetWindowRgn(handle,r,true);
Application.ProcessMessages;
sleep(1);
end;
end;