Ellipse_Bresenham.cpp

#include <GL/glut.h>
#include <math.h>
void initGL()
{
	glClearColor(1.0f, 1.0f, 1.0f, 1.0f); //R=0,G=0,B=0, anpha=1
	glOrtho(-320,320,-240,240,-1,1);	
}
void draw4point(int xc, int yc, int x, int y)
{
	glBegin(GL_POINTS);
		 
		glVertex2i(x + xc, y + yc);
		glVertex2i(x + xc,-y + yc);
		glVertex2i(xc - x, yc - y);
		glVertex2i(xc - x, yc + y);

	glEnd();
}
void EllipsBresenham(int xc,int yc,double a, double b )	
{	 
   	
   	int x = 0;
	int y = b; 
	
	float x0 = a*a/sqrt(a*a + b*b); 
	float P = a*a*(1-2*b)+ b*b;
	draw4point(xc,yc,x,y);
	while (x <= x0) 
    	{
		if (P <0)	
           P += (2*b*b)*(2*x + 3);
            
		else
           {	
            
            P += (2*b*b)*(2*x+3) + 4*a*a*(1-y);
		    y--;
		   }
		x++;
        draw4point(xc,yc,x,y);
		}
	
	x=a;
	y=0;
	
	P=b*b*(1-2*a)+ a*a;
	draw4point(xc,yc,x,y);
	while (x > x0) 
    	{
		if (P <0)	
            P +=(2*a*a)*(2*y + 3);
		else
           {	
            P += (2*a*a)*(2*y + 3) + 4*b*b*(1-x);
            
		    x--;
		   }
		y++;
        draw4point(xc,yc,x,y);
		}
		
}

void mydisplay()
{
    glClear(GL_COLOR_BUFFER_BIT);
	glColor3f(1.0, 0.0, 0.0);
	EllipsBresenham(0, 0, 300,200); //Tâm C(0,0) bán kính 200
	glViewport(0,0,640,480);
	glFlush();

}

int main(int argc, char** argv){
	int mode=GLUT_SINGLE | GLUT_RGB;
	glutInitDisplayMode(mode);
	
	glutInitWindowSize(640, 480);
	glutInitWindowPosition(0, 0);
	glutCreateWindow("DEMO THUAT TOAN VE DUONG ELLIPSE - BRESENHAM");
	 
    initGL();
	glutDisplayFunc(mydisplay);    
	glutMainLoop();
}