算法画圆 中点圆算法 计算机图形学.doc

算法画圆 中点圆算法 计算机图形学Bresenham算法画圆中点圆算法计算机图形学2010-12-02 20：48/中点圆整数算法画圆/void roundMid(int x1,int y1,int R,CDC*pDC)int x=0,y=R；int d=1-R；/起点(0,R),下一点中点(1,R-0.5),d=1*1+(R-0.5)*(R-0.5)-R*R=1.25-R,d只参与整数运算，所以小数部分可省略while(y x)/y x即第一象限的第2区八分圆pDC-SetPixel(x+x1,y+y1,RGB(255,0,0)；/圆心(x1,y1),画点时直接相加平移,画2区pDC-SetPixel(y+x1,x+y1,RGB(255,0,0)；/画1区pDC-SetPixel(-x+x1,y+y1,RGB(255,0,0)；/画3区pDC-SetPixel(-y+x1,x+y1,RGB(255,0,0)；/画4区pDC-SetPixel(-x+x1,-y+y1,RGB(255,0,0)；/画5区pDC-SetPixel(-y+x1,-x+y1,RGB(255,0,0)；/画6区pDC-SetPixel(x+x1,-y+y1,RGB(255,0,0)；/画7区pDC-SetPixel(y+x1,-x+y1,RGB(255,0,0)；/画8区if(d 0)d=d+2*x+3；/d的变化elsed=d+2*(x-y)+5；/d=0时,d的变化y-；/y坐标减1x+；/x坐标加1/Bresenham算法画圆/void RoundBre(int x1,int y1,int R,CDC*pDC)/圆心(x1,y1),当前像素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；/圆心距差值平方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；/起点(0,R)yi=R；dd=2-2*R；/起点的右下像素(1,R-1)的圆心距差值dd=1+(R-1)*(R-1)-R*R pDC-SetPixel(x1,y1,RGB(0,0,255)；/画圆心,证明圆心必须占用一个像素while(yi=xi)/循环到八分之一圆；yi=0即可以画出四分圆pDC-SetPixel(xi+x1,yi+y1,RGB(255,0,0)；/2区,坐标平移(x1,y1)画圆pDC-SetPixel(yi+x1,xi+y1,RGB(255,0,0)；/1区pDC-SetPixel(-xi+x1,yi+y1,RGB(255,0,0)；/3区pDC-SetPixel(-yi+x1,xi+y1,RGB(255,0,0)；/4区pDC-SetPixel(-yi+x1,-xi+y1,RGB(255,0,0)；/5区pDC-SetPixel(-xi+x1,-yi+y1,RGB(255,0,0)；/6区pDC-SetPixel(xi+x1,-yi+y1,RGB(255,0,0)；/7区pDC-SetPixel(yi+x1,-xi+y1,RGB(255,0,0)；/8区if(dd 0)/D在圆内；H在圆上或圆外；选择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时取右点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在圆外；V在圆外或圆上；选择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时取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在圆