简单的 "双缓冲" 绘图的例子

http://www.cnblogs.com/del/archive/2010/04/19/1715779.html

所谓双缓冲就是先画到内存画布(如: TBitmap), 然后再转帖到目的地.

譬如下面小程序:

procedure TForm1.FormCreate(Sender: TObject);
begin
  Timer1.Interval := 100;
  Color := clWhite;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
begin
  Canvas.Pen.Color := Random($FFFFFF);
  Canvas.MoveTo(Random(ClientWidth), Random(ClientHeight));
  Canvas.LineTo(Random(ClientWidth), Random(ClientHeight));
end;

var
  bit: TBitmap;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Timer1.Interval := 100;
  bit := TBitmap.Create;
  bit.Width := ClientWidth;
  bit.Height := ClientHeight;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
begin
  bit.Canvas.Pen.Color := Random($FFFFFF);
  bit.Canvas.MoveTo(Random(bit.Width), Random(bit.Height));
  bit.Canvas.LineTo(Random(bit.Width), Random(bit.Height));
  Self.Canvas.Draw(0, 0, bit);
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  bit.Free;
end;