/* Two-Dimensional Sierpinski Gasket          */
/* Generated Using Randomly Selected Vertices */
/* And Bisection                              */

#ifdef mac_osx
#include <GLUT/glut.h>  // GLUT for the Macintosh
#else
#include <GL/glut.h>  // GLUT for Linux and Unix.
#endif

/* Initial dimensions and attributes of the GUI Window */
#define INITIAL_WINDOW_WIDTH  512
#define INITIAL_WINDOW_HEIGHT 512
#define INITIAL_HORIZONTAL_OFFSET 10
#define INITIAL_VERTICAL_OFFSET 40
#define WINDOW_TITLE "Sierpinski Gasket"

/* World coordinate extrema */
#define XMIN 0.0
#define XMAX 500.0
#define YMIN 0.0
#define YMAX 500.0

/* Algorithm parameter */
#define MAX_ITERATIONS 100000

/* Global variables */
int windowWidth  = INITIAL_WINDOW_WIDTH;
int windowHeight = INITIAL_WINDOW_HEIGHT;

/* Function prototypes */
void display(void);
void reshape(int w, int h);

/* reshape is called each time the user changes the GUI window dimensions. It updates the viewport
   and the world coordinate -> device coordinate transformation */
void reshape(int w, int h) { 
   windowWidth  = w;											/* Update the GUI window dimensions */
   windowHeight = h;
   																/* We will draw in the entire window */
   glViewport(0, 0, (GLsizei) windowWidth, (GLsizei) windowHeight);
   																/* using an orthographic projection */
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   gluOrtho2D(XMIN, XMAX, YMIN, YMAX);
   glMatrixMode(GL_MODELVIEW);
   
   glClearColor(1.0, 1.0, 1.0, 1.0); /* white background */
   glColor3f(1.0, 0.0, 0.0);         /* draw in red */
}

/* display is called each time a portion of the window is exposed, or the window is resized. It
   is always called after reshape. It generates a recursive illustration of Sierpinski's triangular
   gasket. */
void display( void ) {

	/* define a point data type */
    typedef GLfloat point2[2];     

    point2 vertices[3]={{XMIN, YMIN},{(XMIN+XMAX)/2, YMAX},{XMAX, YMIN}}; /* The boundary triangle */

    int j, k;
    int rand();       				       /* standard random number generator */
    point2 p = {(XMIN + XMAX)/2, YMIN};    /* An initial point (world coordinate) */

    glClear(GL_COLOR_BUFFER_BIT);  /*clear the window (paint it with the background color)*/


	/* compute and plot MAX_INTERATIONS new points */
    for( k=0; k < MAX_ITERATIONS; k++) {
         j=rand() % 3; /* pick a vertex at random */

			/* Compute point halfway between selected vertex and old point */
         p[0] = (p[0] + vertices[j][0]) / 2.0; 
         p[1] = (p[1] + vertices[j][1]) / 2.0;
   
     /* plot one new point each iteration */
          glBegin(GL_POINTS);
               glVertex2fv(p); 
          glEnd(); 
     }
     glFlush(); /* clear buffers */
 }

int main(int argc, char** argv) {
	glutInit(&argc,argv);
	glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); /* default, not needed */
	glutInitWindowSize(INITIAL_WINDOW_WIDTH, INITIAL_WINDOW_HEIGHT); 
	glutInitWindowPosition(INITIAL_HORIZONTAL_OFFSET, INITIAL_VERTICAL_OFFSET); 
	glutCreateWindow(WINDOW_TITLE); 
	glutReshapeFunc(reshape); /* register reshape as a callback function */
	glutDisplayFunc(display); /* register display as a callback function */
	glutMainLoop();           /* enter event loop */
	return 0;                 
}