Delphi 的绘图功能[12] - TPen 类(下) : 学习橡皮线

//奇妙的异或运算, 就这些简单的代码, 反复点击按钮...



procedure TForm1.Button1Click(Sender: TObject);

begin

  Canvas.Pen.Color := clYellow; {指定笔颜色为黄色}

  Canvas.Pen.Width := 20;       {笔宽 20}

  Canvas.Pen.Mode := pmXor;     {指定画笔模式为: 画笔色与背景色的异或运算}



  {画线}

  Canvas.MoveTo(0,0);

  Canvas.LineTo(ClientWidth,ClientHeight);

end;


 
   




//效果图:

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//做一个橡皮线的示例:



unit Unit1;



interface



uses

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

  Dialogs, StdCtrls;



type

  TForm1 = class(TForm)

    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;

      Shift: TShiftState; X, Y: Integer);

    procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X, Y: Integer);

    procedure FormMouseUp(Sender: TObject; Button: TMouseButton;

      Shift: TShiftState; X, Y: Integer);

  end;



var

  Form1: TForm1;



implementation



{$R *.dfm}



var

  x1,y1,x2,y2: Integer; {直线两个端点的坐标}

  f: Boolean;           {判断鼠标是否点下}





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

  Shift: TShiftState; X, Y: Integer);

begin

  x1 := X; y1 := Y;

  x2 := X; y2 := Y;

  Canvas.Pen.Color := clRed;

  Canvas.Pen.Width := 2;

  Canvas.Pen.Mode := pmXor;

  f := True;

end;



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

  Y: Integer);

begin

  if f then

  begin

    {擦除}

    Canvas.MoveTo(x1, y1);

    Canvas.LineTo(x2, y2);



    x2 := X; y2 := y;



    {重绘}

    Canvas.MoveTo(x1, y1);

    Canvas.LineTo(x2, y2);

  end;

end;



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

  Shift: TShiftState; X, Y: Integer);

begin

  if f then

  begin

    {画出确定的线}

    Canvas.Pen.Mode := pmCopy;

    Canvas.MoveTo(x1, y1);

    Canvas.LineTo(x2, y2);

    f := not f;

  end;

end;



end.


 
   




//效果图:

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