Window画图程序中画曲线的简单实现

下面是很入以前的一个程序,模仿windows的画图程序中画曲线.其实原理简单得要命 ,就是一个polybezier函数.
那一位有兴趣的可以封装成一个类,方便以后用.
unit unit1;

interface

uses
  windows, messages, sysutils, variants, classes, graphics, controls, forms,
  dialogs, stdctrls;

type
  tstep=(sstartend,sctrl1,sctrl2);
  tform1 = class(tform)
    button1: tbutton;
    procedure formcreate(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 formpaint(sender: tobject);
  private
    { private declarations }
    isdown:boolean;
    isok:boolean;  //标识一次bezier线的绘制是否完成
    step:tstep; //指示到那个阶段了
    startp:tpoint;  //以下是四个点坐标
    endp:tpoint;
    ctrp1:tpoint;
    ctrp2:tpoint;
  public
    { public declarations }
  end;

var
  form1: tform1;

implementation

{$r *.dfm}

procedure tform1.formcreate(sender: tobject);
begin
  self.doublebuffered:=true;
  isdown:=false;
  step:=sstartend;
  isok:=false;
end;

procedure tform1.formmousedown(sender: tobject; button: tmousebutton;
  shift: tshiftstate; x, y: integer);
begin
  isdown:=true;
  if button=mbleft then
  begin
    if (step=sstartend) then
    begin
      startp.x:=x;
      startp.y:=y;
      endp:=point(x,y);
      isok:=false;
    end
    else if (step=sctrl1)  then
    begin
      ctrp1:=point(x,y);
      ctrp2:=point(x,y);
    end
    else if (step=sctrl2)  then
    begin
      ctrp2:=point(x,y);
    end;
  end;
end;

procedure tform1.formmousemove(sender: tobject; shift: tshiftstate; x,
  y: integer);
begin
  if isdown and (shift=[ssleft]) then
  begin
    if (step=sstartend) then
    begin
      endp.x:=x;
      endp.y:=y;
    end
    else if step=sctrl1 then
    begin
      ctrp1:=point(x,y);
      ctrp2:=point(x,y);
    end
    else if (step=sctrl2)  then
    begin
      ctrp2:=point(x,y);
    end;
    self.invalidate;
  end;
end;

procedure tform1.formmouseup(sender: tobject; button: tmousebutton;
  shift: tshiftstate; x, y: integer);
begin
  if isdown and (button=mbleft) then
  begin
    isdown:=false;
    if step=sstartend then step:=sctrl1
    else if step=sctrl1 then step:=sctrl2
    else if step=sctrl2 then begin step:=sstartend; isok:=true; end;
  end;
end;

procedure tform1.formpaint(sender: tobject);
begin
  if not isok then
  begin
    if step=sstartend then
    begin
      self.canvas.moveto(startp.x,startp.y);
      self.canvas.lineto(endp.x,endp.y);
    end
    else begin
     self.canvas.polybezier([startp,ctrp1,ctrp2,endp]);
    end;
  end else begin
    self.canvas.polybezier([startp,ctrp1,ctrp2,endp]);
  end;
end;

end.