////////////////////////////////////////////////////////////////////
//中點(diǎn)圓整數(shù)算法 畫圓 //
/////////////////////////////////////////////////////////////////////
void roundMid(int x1,int y1,int R,CDC* pDC)
{
int x=0,y=R;
int d=1-R; //起點(diǎn)(0,R),下一點(diǎn)中點(diǎn)(1,R-0.5),d=1*1+(R-0.5)*(R-0.5)-R*R=1.25-R,d只參與整數(shù)運(yùn)算，所以小數(shù)部分可省略
while(y>x) //y>x即第一象限的第2區(qū)八分圓
{
pDC->SetPixel(x+x1,y+y1,RGB(255,0,0)); //圓心(x1,y1),畫點(diǎn)時(shí)直接相加平移,畫2區(qū)
pDC->SetPixel(y+x1,x+y1,RGB(255,0,0)); //畫1區(qū)
pDC->SetPixel(-x+x1,y+y1,RGB(255,0,0)); //畫3區(qū)
pDC->SetPixel(-y+x1,x+y1,RGB(255,0,0)); //畫4區(qū)
pDC->SetPixel(-x+x1,-y+y1,RGB(255,0,0)); //畫5區(qū)
pDC->SetPixel(-y+x1,-x+y1,RGB(255,0,0)); //畫6區(qū)
pDC->SetPixel(x+x1,-y+y1,RGB(255,0,0)); //畫7區(qū)
pDC->SetPixel(y+x1,-x+y1,RGB(255,0,0)); //畫8區(qū)
if(d<0)
d=d+2*x+3; //d的變化
else
{
d=d+2*(x-y)+5; //d<=0時(shí),d的變化
y--; //y坐標(biāo)減1
}
x++; //x坐標(biāo)加1
}
}
////////////////////////////////////////////////////////////////////
//Bresenham算法畫圓 //
/////////////////////////////////////////////////////////////////////
void RoundBre(int x1,int y1,int R,CDC* pDC)
{
//圓心(x1,y1),當(dāng)前像素I(xi,yi),右像素H(xi+1,y),右下像素D(xi+1,yi-1),下像素V(xi,yi-1)
int xi,yi,dd,m,n;
//圓心距差值平方dh=(xi+1)*(xi+1)+yi*yi-R*R; dd=(xi+1)*(xi+1)+(yi-1)*(yi-1)-R*R; dv=xi*xi+(yi-1)*(yi-1)-R*R;
xi=0; //起點(diǎn)(0,R)
yi=R;
dd=2-2*R; //起點(diǎn)的右下像素(1,R-1)的圓心距差值dd=1+(R-1)*(R-1)-R*R
pDC->SetPixel(x1,y1,RGB(0,0,255)); //畫圓心,證明圓心必須占用一個(gè)像素
while(yi>=xi) //循環(huán)到八分之一圓;yi>=0即可以畫出四分圓
{
pDC->SetPixel(xi+x1,yi+y1,RGB(255,0,0)); //2區(qū),坐標(biāo)平移(x1,y1)畫圓
pDC->SetPixel(yi+x1,xi+y1,RGB(255,0,0)); //1區(qū)
pDC->SetPixel(-xi+x1,yi+y1,RGB(255,0,0)); //3區(qū)
pDC->SetPixel(-yi+x1,xi+y1,RGB(255,0,0)); //4區(qū)
pDC->SetPixel(-yi+x1,-xi+y1,RGB(255,0,0)); //5區(qū)
pDC->SetPixel(-xi+x1,-yi+y1,RGB(255,0,0)); //6區(qū)
pDC->SetPixel(xi+x1,-yi+y1,RGB(255,0,0)); //7區(qū)
pDC->SetPixel(yi+x1,-xi+y1,RGB(255,0,0)); //8區(qū)
if(dd<0) //D在圓內(nèi);H在圓上或圓外;選擇H或D,dh>=0,dd<0,m=|dh|-|dd|=2*(dd+yi)-1;
{
m=2*(dd+yi)-1;
if(m<=0) //取右像素H(xi+1,yi);m=0時(shí) 取右點(diǎn)
{
dd=dd+2*xi+3; //求H的右下像素(xi+2,yi-1),dd=(xi+2)*(xi+2)+(yi-1)*(yi-1)-R*R
xi=xi+1;
}
else //取右下像素D(xi+1,yi-1)
{
dd=dd+2*(xi-yi+3); //求D的右下像素(xi+2,yi-2),dd=(xi+2)*(xi+2)+(yi-2)*(yi-2)-R*R
xi=xi+1;
yi=yi-1;
}
}
else if(dd>0) //D在圓外;V在圓外或圓上;選擇D或V;dd>0,dv<=0,n=|dd|-|dv|=2*(dd-xi)-1;
{
n=2*(dd-xi)-1;
if(n<=0) //取右下像素D(xi+1,yi-1);n=0時(shí)取
{
dd=dd+2*(xi-yi+3); //求D的右下像素(xi+2,yi-2),dd=(xi+2)*(xi+2)+(yi-2)*(yi-2)-R*R
xi=xi+1;
yi=yi-1;
}
else //取下像素V(xi,yi-1)
{
dd=dd-2*yi+3; //求V的右下像素(xi+1,yi-2)dd=(xi+1)*(xi+1)+(yi-2)*(yi-2)-R*R
yi=yi-1;
}
}
else if(dd==0) //D在圓上,取D(xi+1,yi-1)
{
dd=dd+2*(xi-yi+3); //求D的右下像素(xi+2,yi-2),dd=(xi+2)*(xi+2)+(yi-2)*(yi-2)-R*R
xi=xi+1;
yi=yi-1;
}
}
}