スパイラル曲線を描画
void drawspiral(HDC hdc,int cx,int cy)
{
const double numRevs=20;
const double iNumPoints=numRevs*2*(cx+cy);
cx/=2;
cy/=2;
const double np=iNumPoints/numRevs;
double x=cx*2.0;
double y=cy;
for(int i=0;i<iNumPoints;i+=50)
{
double fAngle=i*2.0*3.14159265/np;
double fScale=1.0-i/iNumPoints;
MoveToEx(hdc,x,y,0);
x=cx*(1.0+fScale*cos(fAngle));
y=cy*(1.0+fScale*sin(fAngle));
LineTo(hdc,x,y);
}
}