#include<math.h>
#include<cairo-features.h>
#include<cairo.h>
#include<cairo-xlib.h>

void
plot (cairo_t* cr,
      int n,
      double r,
      int width,
      int height)
{

   int i;
   double pi = 3.141592653589;
   double d_theta = 2 * pi / n;

   cairo_set_source_rgba (cr, 1, 0, 0, 1);
   cairo_move_to (cr, width/2 + r * cos (0), height/2 + r * sin (0));

   for (i = 0; i < n; i++)
   {
      double theta = i * d_theta;
      cairo_line_to (cr, width/2 + r * cos (theta), height/2 + r * sin (theta));
   }

   cairo_close_path (cr);
   cairo_fill (cr);   
   //cairo_stroke (cr);   

}

void
plot_png (int n,
          double r,
          int width,
          int height)
{

   cairo_t* cr;
   cairo_surface_t* cs_ptr;

   cs_ptr = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, width, height);
   cr = cairo_create (cs_ptr);
   cairo_set_fill_rule (cr, CAIRO_FILL_RULE_EVEN_ODD);  

   plot (cr, n, r, width, height);

   cairo_surface_write_to_png (cs_ptr, "test.png");
   cairo_surface_destroy (cs_ptr);
   cairo_destroy (cr);

}

void
plot_x (int n,
        double r,
        int width,
        int height)
{

   GC gc;
   int screen;
   Pixmap pixmap;   
   Display* display;
   Window root, window;
   unsigned long pixel;

   cairo_t* cr;
   cairo_surface_t* cs_ptr;

   display = XOpenDisplay (NULL);
   screen = DefaultScreen (display);
   root = DefaultRootWindow (display);
   pixel = WhitePixel (display, screen);
   window = XCreateSimpleWindow (display, root,
      0, 0, width, height, 0, 0, pixel);   

   XMapWindow (display, window);
   XSelectInput (display, window, StructureNotifyMask);

   pixmap = XCreatePixmap (display, window, width, height,
      DefaultDepth (display, screen));

   cs_ptr = cairo_xlib_surface_create (display, pixmap,
      DefaultVisual (display, screen), width, height);

   gc = XCreateGC (display, window, 0, 0); 
   XCopyArea (display, pixmap, window, gc, 0, 0, width, height, 0, 0);
   XFlush (display);

   cr = cairo_create (cs_ptr);
   cairo_set_fill_rule (cr, CAIRO_FILL_RULE_EVEN_ODD);    

   plot (cr, n, r, width, height);

   XCopyArea (display, pixmap, window, gc, 0, 0, width, height, 0, 0);
   XFlush (display); 

   sleep (2);

   XFreePixmap (display, pixmap);
   XDestroyWindow (display, window); 

   cairo_destroy (cr);
   cairo_surface_destroy (cs_ptr);

}

int
main (int argc,
      char** argv)
{

   int width = 800;
   int height = 600;

   int n = atoi (argv[1]);
   plot_x (n, 200, width, height);
//   plot_png (n, 200, width, height);

};