/* gasket2.c   */

/* E. Angel, Interactive Computer Graphics */
/* A Top-Down Approach with OpenGL, Third Edition */
/* Addison-Wesley Longman, 2003 */

/* Updated by Bary W Pollack */

/* Recursive subdivision of triangle to a form Sierpinski Gasket */

#include <GL/glut.h>
#include <stdio.h>

typedef float point2[2];

/* initial triangle */
point2 v[] = { {-1.0, -0.58}, {1.0, -0.58}, {0.0, 1.15} };

int n;      /* global: number of subdivisions to be used */

void triangle (point2 a, point2 b, point2 c)
{   /* display one triangle  */
    glBegin (GL_TRIANGLES);
       glVertex2fv (a);
       glVertex2fv (b);
       glVertex2fv (c);
    glEnd ();
}

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);
    divide_triangle (v[0], v[1], v[2], n);
    glFlush ();
}

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);
}

int main (int argc, char **argv)
{
    char sTitle [256];
    n = 4;
    sprintf (sTitle, "2D Gastket - %d subdivisions", n);
    glutInit (&argc, argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB );
    glutInitWindowSize (500, 500);
    glutCreateWindow (sTitle);
    glutDisplayFunc (display);
    myinit ();
    glutMainLoop ();
    return 0;
}