1 unit Unit1;
 2 
 3 interface
 4 
 5 
 6 uses
 7   Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 8   Dialogs, ExtCtrls;
 9 
10 type
11   TForm1 = class(TForm)
12     Image1: TImage;
13     procedure Image1MouseDown(Sender: TObject; Button: TMouseButton;
14       Shift: TShiftState; X, Y: Integer);
15     procedure Image1MouseMove(Sender: TObject; Shift: TShiftState; X,
16       Y: Integer);
17     procedure Image1MouseUp(Sender: TObject; Button: TMouseButton;
18       Shift: TShiftState; X, Y: Integer);
19   private
20     { Private declarations }
21   public
22     { Public declarations }
23   end;
24 
25 var
26   Form1: TForm1;
27   Prior,Origin:TPoint;{Oringin用于记录起始位置也就是鼠标按下的位置，Prior用于记录最后的位置也就是放开鼠标的位置}
28   IsDown:boolean=false;{用于判断鼠标是否仍处于按下的状态}
29 
30 implementation
31 
32 {$R *.dfm}
33 
34 procedure TForm1.Image1MouseDown(Sender: TObject; Button: TMouseButton;
35   Shift: TShiftState; X, Y: Integer);
36 begin
37   IsDown:=true;
38   Image1.Canvas.Moveto(x,y);
39   Origin:=Point(x,y);
40   Prior:=Point(x,y){记录下按下时的位置，此时Origin和Prior重合}
41 end;
42 
43 procedure TForm1.Image1MouseMove(Sender: TObject; Shift: TShiftState; X,
44   Y: Integer);
45 
46 var
47   pX,pY:integer;
48 begin
49   Form1.DoubleBuffered:=true;
50   if isDown then
51   begin
52     pX:=Prior.X;
53     pY:=prior.Y;{着两个值用于保存上一次的位置}
54     Prior:=Point(x,y);
55     Image1.Canvas.MoveTo(Origin.x,origin.Y);
56     Image1.Canvas.Lineto(Prior.X,Prior.Y);{显示现在的线}
57     Image1.Canvas.Pen.Mode:=pmNotXor;{通过异或操作删掉上一条线}
58     Image1.Canvas.MoveTo(Origin.x,origin.Y); 
59     Image1.Canvas.Lineto(pX,pY);
60 
61 
62   end;
63 
64 end;
65 
66 procedure TForm1.Image1MouseUp(Sender: TObject; Button: TMouseButton;
67   Shift: TShiftState; X, Y: Integer);
68 begin
69   IsDown:=false ;
70   Image1.Canvas.Pen.Mode:=pmCopy;
71    
72     Image1.Canvas.MoveTo(Origin.x,origin.Y);
73     Image1.Canvas.Lineto(Prior.X,Prior.Y); {放开鼠标，画出最后的线}
74 
75 end;
76 
77 end.