1. 演算法

2. 原始碼

#include "stdafx.h"


#include "GL/glut.h"
#include "stdlib.h"

void init()
{
	glClearColor(1.0,1.0,1.0,0.0);
	
	glMatrixMode(GL_PROJECTION);
	gluOrtho2D(0.0,600.0,0.0,400.0);
}

inline int round(int x)
{
	return int(x+0.5);
}

void setPixel(int x, int y)
{
	glBegin(GL_POINTS);
	glVertex2i(x,y);
	glEnd();
}

void ellipsePlotPoints(int xc,int yc,int x,int y)
{
	setPixel(xc+x,yc+y);
	setPixel(xc-x,yc+y);
	setPixel(xc-x,yc-y);
	setPixel(xc+x,yc-y);
}

void ellipseMidPoint(int xc,int yc,int rx,int ry)
{
    int x, y, p1,p2;
	int rx2=rx*rx,ry2=ry*ry;
	x=0;
	y=ry;

	/*region 1*/
	ellipsePlotPoints(xc,yc,x,y);
	p1=round(rx2-(rx2*ry)+(0.25*rx2));
	while(ry2*x<=rx2*y)
	{
		if(p1<=0)
		{
            p1+=ry2*(2*x+3);
			x++;
		}
		else
		{
			p1+=ry2*(2*x+3)+rx2*(2-2*y);
            x++;
			y--;
		}
         ellipsePlotPoints(xc,yc,x,y);
	}

	/*region 2*/
	p2=round(ry2*(x+0.5)*(x+0.5)+rx2*(y-1)*(y-1)-rx2*ry2);
	while(y>=0)
	{
		if(p2<=0)
		{
			p2+=ry2*(2*x+2)+rx2*(3-2*y);
			x++;
	        y--;
		}
		else
		{
            p2+=rx2*(3-2*y);
			y--;
		}
		ellipsePlotPoints(xc,yc,x,y);
	}
}

void render()
{
	glClear(GL_COLOR_BUFFER_BIT);
	glColor3f(1.0,0.0,0.0);
	
	ellipseMidPoint(200,200,180,150);
	ellipseMidPoint(400,200,80,160);
	
	glFlush();
}

int main(int argc, char* argv[])
{
	glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
	glutInitWindowPosition(50,100);
	glutInitWindowSize(600,400);
	glutCreateWindow("ellipse");
	
	init();
	glutDisplayFunc(render);
	glutMainLoop();
	
	return 0;
}
 

3. 實驗結果