楼主要的是否是这效果?
procedure TForm1.Button1Click(Sender: TObject);
var
I: Integer;
begin
Button1.Enabled := False;
Canvas.Brush.Color := clBlack;
Canvas.FillRect(ClientRect);
for I := 0 to 255 do
begin
Canvas.Brush.Color := RGB(I, I, I);
Canvas.Ellipse(100, 100, 300, 300);
Application.ProcessMessages;
Sleep(1);
end;
for I := 255 downto 0 do
begin
Canvas.Brush.Color := RGB(I, I, I);
Canvas.Ellipse(100, 100, 300, 300);
Application.ProcessMessages;
Sleep(1);
end;
Button1.Enabled := true;
end;