/********************************************************************
  File: my_gasket.cc 
  Recursive subdivision of triangle to form Sierpinski gasket.

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

  Modified by D. Vrajitoru.
********************************************************************/

#include <GL/glut.h>

typedef float point2[2];

/* initial triangle */

point2 v[]={{-1.0, -0.58}, {1.0, -0.58}, {0.0, 1.15}};

int n;

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

//triangle subdivision using vertex numbers
void divide_triangle(point2 a, point2 b, point2 c, int m)
{
  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(-1.25, 1.25, -1.25, 1.25);
  glMatrixMode(GL_MODELVIEW);
  glClearColor (1.0, 0.95, 0.9, 1.0);
  glColor3f(1.0,0.0,0.0);
}

int main(int argc, char **argv)
{
  n=4;
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB );
  glutInitWindowSize(300, 300);
  glutCreateWindow("2D Gasket");
  glutDisplayFunc(display);
  myinit();
  glutMainLoop();
}