// Sierpinski Gasket in OpenGL

#include <gl/glut.h>


void myinit(void)
{
 		glClearColor(1.0, 1.0, 1.0, 1.0); /* white background */
		glColor3f(1.0, 0.0, 0.0); /* draw in red */

/* set up viewing */
/* 500 x 500 window with origin lower left */

		glMatrixMode(GL_PROJECTION);
		glLoadIdentity();
		gluOrtho2D(0.0, 500.0, 0.0, 500.0);
		glMatrixMode(GL_MODELVIEW);
}

void display( void )
{
/* define a point data type */

    typedef GLfloat point2[2];     

    point2 vertices[3]={{0.0,0.0},{250.0,500.0},{500.0,0.0}}; /* A triangle */

    int i, j, k;
/*     long rand();       standard random number generator */
    point2 p ={75.0,50.0};  /* An srbitrary initial point */

    glClear(GL_COLOR_BUFFER_BIT);  /*clear the window */

/* computes and plots 5000 new points */

    for( k=0; k<5000; k++)
    {
	      j=rand()%3; /* pick a vertex at random */

     /* Compute point halfway between vertex and old point */

	      p[0] = (p[0]+vertices[j][0])/2.0; 
	      p[1] = (p[1]+vertices[j][1])/2.0;
	
     /* plot new point */

	       glBegin(GL_POINTS);
		         glVertex2fv(p); 
	       glEnd();
     }
     glFlush(); /* clear buffers */
}

void main(int argc, char** argv)
{
/* Standard GLUT initialization */

	    glutInit(&argc,argv);
	    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); /* default, not needed */
	    glutInitWindowSize(500,500); /* 500 x 500 pixel window */
	    glutInitWindowPosition(0,0); /* place window top left on display */
	    glutCreateWindow("Sierpinski Gasket"); /* window title */
	    glutDisplayFunc(display); /* display callback invoked when window opened */
		myinit(); /* set attributes */
	    glutMainLoop(); /* enter event loop */
}