//linda macphee-cobb fall 99
//demonstrate midpoint line drawing algorithm for a circle
//input r 
//output x, y each iteration and draw in a window


//www.timestocome.com
//to compile on OSX
//gcc circle.c -o circle -framework GLUT -framework OpenGL


#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <GLUT/glut.h>






//globals
//opengl rountines are predefined so data that is passed to them must
//be declared globably

int r;         //user input radius





//prototypes
void display(void);
void myinit(void);





int main(int argc, char **argv)

{



  //get user input

  system("clear");

  printf("\n Input the radius => ");

  scanf("%d", &r);

 

  //calculate and plot points
  glutInit(&argc, argv);
	glutInitWindowSize(500, 250);           
   	glutInitDisplayMode(GLUT_RGB|GLUT_SINGLE);
	(void)glutCreateWindow("mid-point circle algorithm");
	glutDisplayFunc(display);
	myinit();
  glutMainLoop();



  return 0;



}



//calculate and draw points

void display (void){



	typedef GLfloat point2[2];        //define a point array
	point2 p  = {0.0, 0.0};           //temp for calcluations
	point2 p1, p2, p3, p4, p5, p6, p7;


	int x = 0;
	int y = r;
	int d = 1 - r;
	int deltaE = 3;
	int deltaSE = -2*r + 5;
	int i;


	glClear(GL_COLOR_BUFFER_BIT);	  //clear window



	while(y > x){

		

	  //calculate points

	  if(d < 0){
	    d += deltaE;
	    deltaE += 2;
	    deltaSE += 2;

	  }else{

	    d += deltaSE;
	    deltaE += 2;
	    deltaSE += 4;
	    y--;

	  }

	  x++;

	    

	  //plot points  (*points are cast to floats before plotting...)

	    p[0] = x;	    p[1] = y;
	    p1[0] = y;      p1[1] = x;
	    p2[0] = y;      p2[1] = -x;
		p3[0] = x;      p3[1] = -y;
	    p4[0] = -x;     p4[1] = y;
	    p5[0] = -y;     p5[1] = -x;
	    p6[0] = -y;     p6[1] = x;
	    p7[0] = -x;     p7[1] = -y;





	    glBegin(GL_POINTS);
	      glVertex2fv(p);
	      glVertex2fv(p1);
	      glVertex2fv(p2);
	      glVertex2fv(p3);
	      glVertex2fv(p4);
	      glVertex2fv(p5);
	      glVertex2fv(p6);
	      glVertex2fv(p7);

	    glEnd();



	 



	  //dump points to terminal window

	    //  printf(" x = %d; y = %d\t", x, y);
	    //if(i > 1){
	    //printf("\n");
	    //i=0;
	    //}else{
	    //i++;
	    //}

	

	}



	glFlush();     //plot quickly..  only makes a difference over a network

}





//set up window

void myinit (void){



        //attributes

	glClearColor(1.0, 1.0, 1.0, 0.0);	//backround  (r, g, b, alpha)
	glColor3f(1.0, 0.0, 0.0);		//draw color (r, g, b)



	//set up viewing

	glMatrixMode(GL_PROJECTION);
	gluOrtho2D(-250.0, 250.0, -125.0, 125.0);     //viewing area
	glMatrixMode(GL_MODELVIEW);

}