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.

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