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

/* Author: Brian J. Ross
   October 1999             

   Draw Sierpinski Triangles to level i. 
   The unit triangle is based upon the local origin sitting in its middle.
   The recursive cases presume the sub-triangles are scaled 1/2, and then
   translated to new loci around bigger triangle position.
   Note the order of glTranslatef and glScalef: we scale the object first,
   and translate it to desired position. If these commands are reversed,
   then the scaling will affect translated position, which won't correctly
   position the triangles. (Transformations accumulate!) */

void recursive_tri(int i) {

	if (i <= 1) {  		  /* Base case: draw a triangle */
	   glBegin(GL_TRIANGLES);
	      glVertex2f(-80.0, -80.0);
	      glVertex2f(80.0, -80.0);
	      glVertex2f(0.0, 80.0);
	   glEnd();
	}
	else {
	   --i; 

	   glPushMatrix();	 /* draw lower-left */
	   glTranslatef(-40.0, -40.0, 0.0);
	   glScalef(0.5, 0.5, 1.0);
	   recursive_tri(i);
	   glPopMatrix();

	   glPushMatrix();	 /* draw lower-right */
	   glTranslatef(40.0, -40.0, 0.0);
	   glScalef(0.5, 0.5, 1.0);
	   recursive_tri(i);
	   glPopMatrix();

	   glPushMatrix();	 /* draw top-middle */
	   glTranslatef(0.0, 40.0, 0.0);
	   glScalef(0.5, 0.5, 1.0);
	   recursive_tri(i);
	   glPopMatrix();
	}
}

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

void drawtri() {
	int i;

	for (i=1; i < 9; i++) {
	   glClear(GL_COLOR_BUFFER_BIT);
	   glColor3f(1.0, 1.0, 1.0);	
	   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);
	glutCreateWindow("Sierpinski Triangles");


	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D(-100.0, 100.0, -100.0, 100.0);
       
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	glPushMatrix();

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

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