怎样用C语言画圆？

#include <math.h>

#include <graphics.h> /*预定义库函数*/

void circlePoint(int x,int y)/*八分法画圆程序*/

{

circle(320+x*20,240+y*20,3)

circle(320+y*20,240+x*20,3)

circle(320-y*20,240+x*20,3)

circle(320-x*20,240+y*20,3)

circle(320-x*20,240+y*20,3)

circle(320-x*20,240-y*20,3)

circle(320-y*20,240-x*20,3)

circle(320+y*20,240-x*20,3)

circle(320+x*20,240-y*20,3)

}

void MidBresenhamcircle(int r) /* 中点Bresenham算法画圆的程序 */

{

int x,y,d

x=0y=rd=1-r /* 计算初始值 */

while(x<y)

{ circlePoint(x,y) /* 绘制点(x,y)及其在八分圆中的另外7个对称点 */

if(d<0) d+=2*x+3/* 根据误差项d的判断,决定非最大位移方向上是走还是不走 */

else

{ d+=2*(x-y)+5

y--

}

x++

delay(900000)

} /* while */

}

main()

{

int i,j,r,graphmode,graphdriver

detectgraph(&graphdriver,&graphmode)

initgraph(&graphdriver,&graphmode," ")

printf("中点Bresenhamcircle算法画圆的程序\n")/*提示信息*/

printf("注意 |r|<=11")

printf("\n输入半径值 r:")

scanf("%d",&r)

printf("按任意键显示图形...")

getch()

cleardevice()

setbkcolor(BLACK)

for(i=20i<=620i+=20) /*使用双循环画点函数画出表格中的纵坐标*/

for(j=20j<=460j++)

putpixel(i,j,2)

for(j=20j<=460j+=20) &n欢迎光临学网,收藏本篇文章 [1] [2]

$False$

bsp/*使用双循环画点函数画出表格中的横坐标*/

for(i=20i<=620i++)

putpixel(i,j,2)

outtextxy(320,245,"0")/*原点坐标*/

outtextxy(320-5*20,245,"-5")circle(320-5*20,240,2) /*横坐标值*/

outtextxy(320+5*20,245,"5")circle(320+5*20,240,2)

outtextxy(320-10*20,245,"-10")circle(320-10*20,240,2)

outtextxy(320+10*20,245,"10")circle(320+10*20,240,2)

outtextxy(320-15*20,245,"-15")circle(320-15*20,240,2)

outtextxy(320+15*20,245,"15")circle(320+15*20,240,2)

outtextxy(320,240-5*20,"-5")circle(320,240-5*20,2) /*纵坐标值*/

outtextxy(320,240+5*20,"5")circle(320,240+5*20,2)

outtextxy(320,240-10*20,"-10")circle(320,240-10*20,2)

outtextxy(320,240+10*20,"10")circle(320,240+10*20,2)

outtextxy(20,10,"The center of the circle is (0,0) ") /*坐标轴左上角显示提示信息*/

setcolor(RED)/*标记坐标轴*/

line(20,240,620,240) outtextxy(320+15*20,230,"X")

line(320,20,320,460) outtextxy(330,20,"Y")

setcolor(YELLOW)

MidBresenhamcircle(r)

setcolor(BLUE)/*绘制圆*/

circle(320,240,r*20)

setcolor(2)

getch()

closegraph()

}

的确哈，关键在于对delta的理解

可以看到，都是delta=2*(1-radius)这样的，起作用应该是判断要画的点x、y坐标的变化趋势，先把我注释了的代码贴下，加了getch()可以看到画的过程

-----------------------------------------------------------------

#include<graphics.h>

#include<stdio.h>

void BresenhemCircle(int centerx, int centery, int radius, int color, int type)

void main()

{

int drive=DETECT,mode

int i,j

initgraph(&drive,&mode,"")

BresenhemCircle(300,200,100,15,0)

getch()

}

void BresenhemCircle(int centerx, int centery, int radius, int color, int type)

{

int x =type = 0/*初始横坐标为原点*/

int y = radius/*初始纵坐标远离原点*/

int delta = 2*(1-radius)

int direction

while (y >= 0)

{

getch()

if (!type)/*执行*/

{

/*在上半圆画两点*/

putpixel(centerx+x, centery+y, color)

putpixel(centerx-x, centery+y, color)

/*在下半圆画两点*/

putpixel(centerx-x, centery-y, color)

putpixel(centerx+x, centery-y, color)

getch()

}

else/*不执行*/

{

line(centerx+x, centery+y, centerx+x, centery-y)

line(centerx-x, centery+y, centerx-x, centery-y)

getch()

}

/*以下代码设置下次四点的位置，圆是对称的，且此方法相当于同时画四个圆弧

观察右上方圆弧可知，前一半是x增的要快些，后一半是y减的快些*/

if (delta <0)

{

if ((2*(delta+y)-1) <0)

direction = 1/*选择横向加*/

else

direction = 2

}

else if(delta >0)

{

if ((2*(delta-x)-1) >0)

direction = 3/*选择纵向减*/

else

direction = 2

}

else

direction=2

switch(direction)

{

case 1:

x++/*只横坐标远离原点*/

delta += (2*x+1)/*小执行到这，所以加*/

break

case 2:

x++

y--/*横向远离，同时纵向靠近*/

delta += 2*(x-y+1)/*即(2*x+1)+(-2*y+1)*/

break

case 3:

y--/*只纵坐标靠近原点*/

delta += (-2*y+1)/*大执行到这，所以减*/

break

}

}

}

---