Delphi实例之橡皮筋画图的实现

                        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.