#include <GL/gl.h>
#include <GL/glut.h>
#include <stdlib.h>


/* Author: Brian J. Ross
   October 1999
   
   Draw 3D Sierpinski Pyramids to level i. 
   The unit pyramid is based upon the local origin sitting in its middle.
   The recursive cases presume the sub-pyramids are scaled 1/2, and then
   translated to new loci around bigger triangle position. */

void recursive_tri(int i) {

	if (i <= 1) {  		  /* Base case: draw a pyramid */
	   glBegin(GL_TRIANGLES);
	      glColor3f(drand48(), drand48(), drand48());
	      glVertex3f(-80.0, -80.0, 80.0);
	      glVertex3f(80.0, -80.0, 80.0);
	      glVertex3f(0.0, 80.0, 0.0);

	      glColor3f(drand48(), drand48(), drand48());
	      glVertex3f(80.0, -80.0, 80.0);
	      glVertex3f(0.0, -80.0, -80.0);
	      glVertex3f(0.0, 80.0, 0.0);

	      glColor3f(drand48(), drand48(), drand48());
	      glVertex3f(0.0, -80.0, -80.0);
	      glVertex3f(-80.0, -80.0, 80.0);
	      glVertex3f(0.0, 80.0, 0.0);

	      glColor3f(drand48(), drand48(), drand48());
	      glVertex3f(-80.0, -80.0, 80.0);
	      glVertex3f(80.0, -80.0, 80.0);
	      glVertex3f(0.0, -80.0, -80.0);
	   glEnd();
	}
	else {
	   --i; 

	   glPushMatrix();	 /* draw lower front left */
	   glTranslatef(-40.0, -40.0, 40.0);
	   glScalef(0.5, 0.5, 0.5);
	   recursive_tri(i);
	   glPopMatrix();

	   glPushMatrix();	 /* draw lower front right */
	   glTranslatef(40.0, -40.0, 40.0);
	   glScalef(0.5, 0.5, 0.5);
	   recursive_tri(i);
	   glPopMatrix();

	   glPushMatrix();	 /* draw lower back middle */
	   glTranslatef(0.0, -40.0, -40.0);
	   glScalef(0.5, 0.5, 0.5);
	   recursive_tri(i);
	   glPopMatrix();


	   glPushMatrix();	 /* draw top-middle */
	   glTranslatef(0.0, 40.0, 0.0);
	   glScalef(0.5, 0.5, 0.5);
	   recursive_tri(i);
	   glPopMatrix();
	}
}

/* Draw 8 levels of Sierpinski Pyramids. 
   Give 5 seconds of viewing enjoyment per level. */

void drawtri() {
	int i;

	for (i=1; i < 9; i++) {
	   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	   printf("level = %d\n", i);
	   recursive_tri(i);
	   sleep(5);
	}
}


main(int argc, char **argv) {
	glutInit(&argc, argv);
	glutInitWindowSize(600, 600);
	glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE | GLUT_DEPTH);
	glutCreateWindow("3D Sierpinski Pyramids");


	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(-125.0, 125.0, -125.0, 125.0, -125.0, 125.0);
 	glRotatef(15.0, 1.0, 0.0, 0.0);
	glRotatef(45.0, 0.0, 1.0, 0.0); 
       
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	glPushMatrix();
	glEnable(GL_DEPTH_TEST);

	glClearColor(0.0, 0.0, 0.0, 1.0);  /* black */

	glutDisplayFunc(drawtri);
	glutMainLoop();
	return 0;
}