为何得不到想要的图形？

[1982fish]

我的源程序：
//---------------------------------------------------------------------------

#include <vcl.h>
#pragma hdrstop
#include<math.h>
#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
#define Pi 3.14159265
double a,b;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
: TForm(Owner)
{
}
//---------------------------------------------------------------------------

void __fastcall TForm1::FormCreate(TObject *Sender)
{

for(int i=0;i<19;i++)
{
b=250+250*sin(i*Pi/360.0);
a=250+250*cos(i*Pi/360.0);
}
Shape1->Shape=stCircle;
Image1->Canvas->Ellipse(0,0,500,500);
Image1->Canvas->Ellipse(50,50,450,450);
Image1->Canvas->MoveTo(250,250);
Image1->Canvas->LineTo(a,b);

}
为什么把 Image1->Canvas->MoveTo(250,250);
Image1->Canvas->LineTo(a,b);
放在 Shape1->Shape=stCircle;
Image1->Canvas->Ellipse(0,0,500,500);
Image1->Canvas->Ellipse(50,50,450,450);
前输出结果就不一样？我想输出一个环行被线段平均割成20块
但是上面的循环好像不起作用，请问各位大侠上面程序错在哪里；我应该怎么改？

[ljianq]

你的循环肯定不起作用，应该把画图命令放在循环中。

[hdaq]

这使因为你没有指定Canvas的Brush的类型导致，系统默认是实型填充，所一你先画线的话会被后面的圆清掉。
下面的程序可以达到你的要求：

void __fastcall TForm1::FormCreate(TObject *Sender)
{
int a,b,c,d;
Image1->Picture->Bitmap->Width = 500;
Image1->Picture->Bitmap->Height = 500;
Image1->Picture->Bitmap->PixelFormat = pf24bit;
Image1->Picture->Bitmap->Canvas->Brush->Style = bsClear;
for(int i=0;i<20;i++)
{
b = (int)floor(250.0 + 250.0 * sin((double)i * 360.0 / 20.0 /180.0 * M_PI) + 0.5);
a = (int)floor(250.0 + 250.0 * cos((double)i * 360.0 / 20.0 /180.0 * M_PI) + 0.5);

d = (int)floor(250.0 + 200.0 * sin((double)i * 360.0 / 20.0 /180.0 * M_PI) + 0.5);
c = (int)floor(250.0 + 200.0 * cos((double)i * 360.0 / 20.0 /180.0 * M_PI) + 0.5);
//Shape1->Shape=stCircle;

Image1->Canvas->MoveTo(c,d);
Image1->Canvas->LineTo(a,b);

Image1->Canvas->Ellipse(0,0,500,500);
Image1->Canvas->Ellipse(50,50,450,450);
}
}
//---------------------------------------------------------------------------

[1982fish]

thx