怎么样删除用framrect画的虚线矩形框？ (100分)

我想用鼠标在图片上画任意的矩形框，就象photoshop中选择区域一样，要动态的模拟画虚线矩形框，
这样每次我都必须删除上一次的矩形框。最后放下鼠标左键，矩形框生成。
可是由于我在image1MouseMove事件中每次都执行image1.Repaint，所以闪烁很严重。不知有没有好办法实现这种对图象的选择

canvas.brush.Style := bsDiagCross;
canvas.FrameRect(rect_ll);//画矩形框

//实现流动线效果，如Photoshop中选择图形时的状态，摘自于本论坛
var
Form1: TForm1;
Counter :Byte;

implementation

{$R *.dfm}
procedure MovingDots(X,Y: Integer; TheCanvas: TCanvas); stdcall;
begin
Counter := Counter shl 1;
if Counter = 0 then Counter := 1;
if (Counter and 224) > 0 then
TheCanvas.Pixels[X,Y] :=clBtnFace
else
TheCanvas.Pixels[X,Y] :=clBlack;
end;


procedure TForm1.Timer1Timer(Sender: TObject);
begin
LineDDA(30,30,200,30,@MovingDots,LongInt(Canvas));
LineDDA(200,30,200,150,@MovingDots,LongInt(Canvas));
LineDDA(200,150,30,150,@MovingDots,LongInt(Canvas));
LineDDA(30,150,30,30,@MovingDots,LongInt(Canvas));
end;

一般实现这种情况可用XOR方式操作

倒，被盗版了，^_^

var
Form1: TForm1;
draw :Boolean;
p1,p2 :TPoint;

implementation

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
begin
draw :=False;
Image1.Canvas.Pen.Style :=psDot;
Image1.Canvas.Brush.Style :=bsClear;
end;

procedure TForm1.Image1MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
draw :=True;
p1 :=Point(x,y);
p2 :=p1;
end;

procedure TForm1.Image1MouseMove(Sender: TObject; Shift: TShiftState; X,
Y: Integer);
begin
if draw then
begin
with Image1 do begin
Canvas.Rectangle(p1.x,p1.y,p2.x,p2.y);
Canvas.Pen.Mode :=pmNotXor;
p2 :=Point(x,y);
Canvas.Rectangle(p1.x,p1.y,p2.x,p2.y);
end;
end;
end;

procedure TForm1.Image1MouseUp(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
if draw then
begin
with Image1 do begin
Canvas.Rectangle(p1.x,p1.y,p2.x,p2.y);
Canvas.Pen.Mode :=pmCopy;
p2 :=Point(x,y);
Canvas.Rectangle(p1.x,p1.y,p2.x,p2.y);
end;
end;
draw :=False;
end;

至于如何形成流动线的效果，看看这里：http://www.delphibbs.com/delphibbs/dispq.asp?lid=930660

tyn ,你好象并没有删除矩形框，你能告诉我pmNotXor这种模式的用处吗？
如果我象CLICK 图象时，矩形框消失，可以做到吗？谢谢！

现在好了，先画一个矩形框，然后点击按钮消失。

var
Form1: TForm1;
draw :Boolean;
p1,p2 :TPoint;

implementation

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
begin
draw :=False;
Image1.Canvas.Pen.Style :=psDot;
Image1.Canvas.Brush.Style :=bsClear;

end;

procedure TForm1.Image1MouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
draw :=True;
p1 :=Point(x,y);
p2 :=p1;

end;

procedure TForm1.Image1MouseMove(Sender: TObject; Shift: TShiftState; X,
Y: Integer);
begin

if draw then
begin
with Image1 do begin
Canvas.Rectangle(p1.x,p1.y,p2.x,p2.y);
Canvas.Pen.Mode :=pmNotXor;
p2 :=Point(x,y);
Canvas.Rectangle(p1.x,p1.y,p2.x,p2.y);
end;
end;

end;

procedure TForm1.Image1MouseUp(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
if draw then
begin
with Image1 do begin
Canvas.Rectangle(p1.x,p1.y,p2.x,p2.y);
p2 :=Point(x,y);
Canvas.Rectangle(p1.x,p1.y,p2.x,p2.y);
end;
end;
draw :=False;

end;

procedure TForm1.Button1Click(Sender: TObject);
begin
Image1.Canvas.Rectangle(p1.x,p1.y,p2.x,p2.y);
Image1.Canvas.Pen.Mode :=pmCopy;
end;

接受答案了.