Delphi实例之橡皮筋画图的实现

在《Delphi7基础教程》这本书的练习中提到过一个橡皮筋画图的例子，书上的源码是错误的！不知道是打印的错误还是本身源码就有问题，我将它改了过来。

在Form1上放置一个Image组件，Image1的Align设为Client。

 unit Unit1;

 interface

 uses

   Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,

   Dialogs, ExtCtrls;

 type

   TForm1 = class(TForm)

     Image1: TImage;

     procedure Image1MouseDown(Sender: TObject; Button: TMouseButton;

       Shift: TShiftState; X, Y: Integer);

     procedure Image1MouseMove(Sender: TObject; Shift: TShiftState; X,

       Y: Integer);

     procedure Image1MouseUp(Sender: TObject; Button: TMouseButton;

       Shift: TShiftState; X, Y: Integer);

   private

     { Private declarations }

   public

     { Public declarations }

   end;

 var

   Form1: TForm1;

   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}

   IsDown:boolean=false;{用于判断鼠标是否仍处于按下的状态}

 implementation

 {$R *.dfm}

 procedure TForm1.Image1MouseDown(Sender: TObject; Button: TMouseButton;

   Shift: TShiftState; X, Y: Integer);

 begin

   IsDown:=true;

   Image1.Canvas.Moveto(x,y);

   Origin:=Point(x,y);

   Prior:=Point(x,y){记录下按下时的位置，此时Origin和Prior重合}

 end;

 procedure TForm1.Image1MouseMove(Sender: TObject; Shift: TShiftState; X,

   Y: Integer);

 var

   pX,pY:integer;

 begin

   Form1.DoubleBuffered:=true;

   if isDown then

   begin

     pX:=Prior.X;

     pY:=prior.Y;{着两个值用于保存上一次的位置}

     Prior:=Point(x,y);

     Image1.Canvas.MoveTo(Origin.x,origin.Y);

     Image1.Canvas.Lineto(Prior.X,Prior.Y);{显示现在的线}

     Image1.Canvas.Pen.Mode:=pmNotXor;{通过异或操作删掉上一条线}

     Image1.Canvas.MoveTo(Origin.x,origin.Y);

     Image1.Canvas.Lineto(pX,pY);

   end;

 end;

 procedure TForm1.Image1MouseUp(Sender: TObject; Button: TMouseButton;

   Shift: TShiftState; X, Y: Integer);

 begin

   IsDown:=false ;

   Image1.Canvas.Pen.Mode:=pmCopy;

     Image1.Canvas.MoveTo(Origin.x,origin.Y);

     Image1.Canvas.Lineto(Prior.X,Prior.Y); {放开鼠标，画出最后的线}

 end;

 end.