/* Recursive subdivision of triangle to form Sierpinski gasket */

#include <GL/freeglut.h>

typedef float point2[2];

/* initial triangle */

point2 v[]={{-1.0, -0.58}, {1.0, -0.58}, {0.0, 1.15}};

int n;

void triangle( point2 a, point2 b, point2 c)

/* display one triangle  */
{
    
       glVertex2fv(a);
       glVertex2fv(b);
       glVertex2fv(c);
}

void divide_triangle(point2 a, point2 b, point2 c, int m)
{

/* triangle subdivision using vertex numbers */

    point2 v0, v1, v2;
    int j;
    if(m>0) 
    {
        for(j=0; j<2; j++) v0[j]=(a[j]+b[j])/2;
        for(j=0; j<2; j++) v1[j]=(a[j]+c[j])/2;
        for(j=0; j<2; j++) v2[j]=(b[j]+c[j])/2;
        divide_triangle(a, v0, v1, m-1);
        divide_triangle(c, v1, v2, m-1);
        divide_triangle(b, v2, v0, m-1);
    }
    else(triangle(a,b,c)); /* draw triangle at end of recursion */
}


void display(void)
{


    glClear(GL_COLOR_BUFFER_BIT);
	glBegin(GL_TRIANGLES);
	divide_triangle(v[0], v[1], v[2], n);
    glEnd();
    glFlush();
    
}

void clear(void)
{
	glClear(GL_COLOR_BUFFER_BIT);
}



void mouse(int btn, int state, int x, int y)
{
if(btn==GLUT_LEFT_BUTTON&state==GLUT_DOWN)  glutIdleFunc(display);
if(btn==GLUT_MIDDLE_BUTTON&state==GLUT_DOWN)   exit(0);
if(btn==GLUT_RIGHT_BUTTON&state==GLUT_DOWN)   glutIdleFunc(NULL);
}

void myinit()
{

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(-2.0, 2.0, -2.0, 2.0);
    glMatrixMode(GL_MODELVIEW);
    glClearColor (1.0, 1.0, 1.0, 1.0);
	glColor3f(0.0,0.0,0.0);
}

void
main(int argc, char **argv)
{
    n=4;
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB );
    glutInitWindowSize(500, 500);
    glutCreateWindow("3D Gasket");

    glutIdleFunc (display);
    glutMouseFunc (mouse); 
    glutDisplayFunc(clear);
    myinit();
    glutMainLoop();
}