delphi GDI+ 实现简单画图

unit Unit1;

interface

uses

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

  Dialogs;

type

  TForm1 = class(TForm)

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

      Y: Integer);

    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;

      Shift: TShiftState; X, Y: Integer);

    procedure FormMouseUp(Sender: TObject; Button: TMouseButton;

      Shift: TShiftState; X, Y: Integer);

  private

    { Private declarations }

  public

    { Public declarations }

  end;

var

  Form1: TForm1;

implementation

{$R *.dfm}

uses

  GDIPAPI,GDIPOBJ; //包含这两个GDI+单元

var

  flag:Integer; //声明一个用作标志位的变量，根据它的值来决定是否开始画图

  Downx,Downy:Integer; //记录鼠标点下时的坐标

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

  Shift: TShiftState; X, Y: Integer);

begin

  flag:=1; //鼠标点下了，标志置1

  Downx:=x; //同时记录下点击的坐标

  Downy:=y; 

end;

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

  Y: Integer);

var

  g: TGPGraphics;

  p: TGPPen;

begin

  Form1.DoubleBuffered:=True; //开启双缓冲

  if flag = 1 then      //判断是否开始画图，标志为1就开始画

  begin

    g := TGPGraphics.Create(Canvas.Handle); //创建对象

    p := TGPPen.Create(aclRed,2);

    p.SetStartCap(LineCapRound); //设置线帽，让线看起来更圆润

    p.SetEndCap(LineCapRound);

    g.SetSmoothingMode(SmoothingModeHighQuality); //抗锯齿

    g.DrawLine(p,Downx,Downy,x,y); //画线

    Downx:=x; //保存旧的坐标，留待下一次使用

    Downy:=y;

    p.Free; //对象释放

    g.Free;

  end;

end;

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

  Shift: TShiftState; X, Y: Integer);

begin

  flag:=0; //鼠标抬起了，标志置0，表示不再画图了

end;

end.