中点Bresenham算法画圆

根据鼠标按下和抬起画圆
p0点鼠标按下点，当做圆的中心
p1点鼠标抬起点
而P0，P1的得到，具体由OnLButtonUp（）和OnLButtonDown来实现
由p0和p1可以得到圆的半径r
采用八分法画圆

void DrawCircle(CDC *pDC, CPoint p0, CPoint p1, COLORREF clr)
{
    int q=(p0.x-p1.x)*(p0.x-p1.x)+(p0.y-p1.y)*(p0.y-p1.y);
    int r=(int)sqrt(q);
    int k=r/1.4;
    float d=1.25-r;
    int x=0,y=r;

    while(x!=k){

        if (d<0)  
            d+=2*x+3;  
        else  
        {  
            d+=2*(x-y)+5;  
            y-=1;  
        }  
        pDC->SetPixel(p0.x+x,p0.y+y,clr);  
        pDC->SetPixel(p0.x+x,p0.y-y,clr);  
        pDC->SetPixel(p0.x-x,p0.y+y,clr);  
        pDC->SetPixel(p0.x-x,p0.y-y,clr);  
        pDC->SetPixel(p0.x+y,p0.y-x,clr);  
        pDC->SetPixel(p0.x+y,p0.y+x,clr);  
        pDC->SetPixel(p0.x-y,p0.y+x,clr);  
        pDC->SetPixel(p0.x-y,p0.y-x,clr);  
        x=x+1; 
    }


}