再学 GDI+[13] DrawBezier - 绘制贝塞尔线

unit Unit1;

interface

uses
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);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}
uses
GDIPOBJ,GDIPAPI;
var                 //定义4个指针变量，并赋予初值
pts:array[0..3] of TGPPoint = ((x:30;y:100),(x:120;y:10),(x:170;y:150),(x:220;y:100));
ptn:Integer = -1;
flag:Boolean;     //定义标志变量，它决定了是否该绘画
procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
flag:=True;     //鼠标左键被按下，可以绘画了，所以标志位致True
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
Y: Integer);
var
R:TRect;
i:Integer;
begin
if flag then
begin
if ptn = -1 then Exit;
pts[ptn].X:=x;    //如果鼠标按下，同时还命中了以四个坐标点所画的蓝色矩形，那么保存移动到的新位置
pts[ptn].Y:=y;
Repaint;
end
else
//-----------------鼠标在客户区移动而没有按下鼠标左键时执行以下代码----------------------------
begin
ptn:=-1;
for I := 0 to 3 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 ptn:=i;    //PtInRect是矩形命中函数，参数1是个矩形，参数2是个坐标
end;

end;
//------------------如果鼠标移动到任何一个蓝色矩形，那么么ptn就有正值（不是-1）了，
//-------------------而当鼠标左键按下同时又命中蓝色矩形时，这部分代码就暂时不执行了-------------
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
Shift: TShiftState; X, Y: Integer);
begin
flag:=False;    //鼠标左键抬起就不再画了，所以标志位致False
end;

procedure TForm1.FormPaint(Sender: TObject);
var
g:TGPGraphics;
p:TGPPen;
i:Integer;
begin
Form1.DoubleBuffered:=True;
g:=TGPGraphics.Create(Canvas.Handle);
g.Clear(aclWhite);
p:=TGPPen.Create(aclRed,1);

g.DrawBezier(p,pts[0],pts[1],pts[2],pts[3]);   //根据4个坐标点变量画塞贝尔曲线

p.SetColor(aclBlue); //画笔颜色设为蓝色并开始逐个按4个坐标点变量画4个很小的矩形
for I := 0 to 3 do
begin
g.DrawRectangle(p,MakeRect(Rect(pts[i].X-2,pts[i].Y-2,pts[i].X+2,pts[i].Y+2)));
end;
p.Free;
g.Free;

end;

end.