/*
 *  epicycloid.c
 */

#include <math.h>
#include <stdlib.h>
#include "glut.h"

typedef float vec2[2];

void vadd(vec2 c, vec2 a, vec2 b)
{
    c[0] = a[0] + b[0];
    c[1] = a[1] + b[1];
}

void smul(vec2 b, float s, vec2 a)
{
    b[0] = s * a[0];
    b[1] = s * a[1];
}

float a, b;
float N;

void setup(void)
{
    gluOrtho2D(-1.0, 1.0, -1.0, 1.0);
}

void circle(float t, vec2 v)
{
   float phi = 2*M_PI*t;
   v[0] = cos(phi);
   v[1] = sin(phi);
}

void  epicycloid(float t, vec2 v)
{
   float phi = 2*M_PI*t;
   v[0] = (a+b)*cos(phi) - cos(((a+b)/b)*phi);
   v[1] = (a+b)*sin(phi) - sin(((a+b)/b)*phi);
} 

void display(void)
{
    /* clear background */
    glClearColor(0.95f, 0.95f, 0.95f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT); 

    // circle of radius b rolling on a circle of radius a

    glColor3f(1.0f, 0.25, 0.25f);
    glLineWidth(2.0f);
    glBegin(GL_LINE_LOOP);
        float t;
	for( t = 0.0; t < 10.0; t += 10.0/N ) {
            vec2 u, v, w;
            circle(t, u);
            smul(v, a+b, u);
            circle((a/b+1)*t, u);
            smul(w, -b, u);
            vadd(u, v, w);
            glVertex2fv(u);
            //epicycloid(t,v);
            //glVertex2fv(v);
        }
    glEnd();


    glFlush();
}

int main(int argc, char** argv)
{
    glutInit(&argc,argv); 
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);  
    glutInitWindowSize(512,512);
    glutInitWindowPosition(32,32);
    glutCreateWindow("rect"); 

    a = 0.25;
    b = a/3;
    N = 360*10;
    if( argc > 1 ) {
        if( argc > 2 ) {
            a = atof(argv[1]);
            b = atof(argv[2]);
        }
        if( argc > 3 ) {
            N = atoi(argv[3]);
        }
    }
    printf("a=%g, b=%g, N=%g\n", a, b, N);

    setup();

    glutDisplayFunc(display);

    glutMainLoop();
}