unit Unit1;interfaceuses  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,  Dialogs;type  TForm1 = class(TForm)    procedure FormPaint(Sender: TObject);    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);    procedure FormCreate(Sender: TObject);  end;var  Form1: TForm1;implementation{$R *.dfm}uses GDIPOBJ,GDIPAPI;var  pts: array of TGPPoint;  ptn: Integer = -1;  f: Boolean;procedure TForm1.FormCreate(Sender: TObject);begin  Text := '按住 Ctrl 键可添加点';end;procedure TForm1.FormPaint(Sender: TObject);var  g: TGPGraphics;  p: TGPPen;  i: Integer;begin  g := TGPGraphics.Create(Canvas.Handle);  p := TGPPen.Create(aclRed, 1);  g.Clear(aclWhite);  g.DrawBeziers(p, PGPPoint(pts), Length(pts));  p.SetColor(aclBlue);  for i := Low(pts) to High(pts) do    g.DrawRectangle(p, MakeRect(Rect(pts[i].X-2, pts[i].Y-2, pts[i].X+2, pts[i].Y+2)));  g.Free;  p.Free;end;procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;  Shift: TShiftState; X, Y: Integer);begin  f := True;end;procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,  Y: Integer);var  R: TRect;  i: Integer;begin  if f then  begin    if ptn = -1 then Exit;    pts[ptn].X := X;    pts[ptn].Y := Y;    Repaint;  end else begin    ptn := -1;    Cursor := crDefault;    for i := Low(pts) to High(pts) do    begin      R := Rect(pts[i].X-2, pts[i].Y-2, pts[i].X+2, pts[i].Y+2);      if PtInRect(R, Point(X, Y)) then      begin        ptn := i;        Cursor := crHandPoint;      end;    end;  end;end;procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;  Shift: TShiftState; X, Y: Integer);begin  f := False;  if ssCtrl in Shift then  begin    SetLength(pts, Length(pts)+1);    pts[High(pts)].X := X;    pts[High(pts)].Y := Y;    Canvas.Pen.Color := clBlue;    Canvas.Rectangle(X-2, Y-2, X+2, Y+2);    {当点数是 3*n+1 时再绘制}    if Length(pts) mod 3 = 1 then Repaint;  end;end;end.

object Form1: TForm1  Left = 0  Top = 0  Caption = 'Form1'  ClientHeight = 188  ClientWidth = 254  Color = clBtnFace  Font.Charset = DEFAULT_CHARSET  Font.Color = clWindowText  Font.Height = -11  Font.Name = 'Tahoma'  Font.Style = []  OldCreateOrder = False  Position = poDesktopCenter  OnCreate = FormCreate  OnMouseDown = FormMouseDown  OnMouseMove = FormMouseMove  OnMouseUp = FormMouseUp  OnPaint = FormPaint  PixelsPerInch = 96  TextHeight = 13end