prog/c/guile-gnuplot/main.c

/* This program lets you use guile to script some commands
   to gnuplot.
   https://www.gnu.org/savannah-checkouts/gnu/guile/docs/guile-tut/tutorial.html
*/

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <math.h>
#include <libguile.h>           /* including guile! awesome! */

static const int WIDTH  = 10;
static const int HEIGHT = 10;

static double x, y;
static double direction;
static int pendown;
static FILE * global_output;

static void
tortoise_reset ()
{
  x = y = 0.0;
  direction = 0.0;
  pendown = 1;

  fprintf (global_output, "clear\n");
  fflush (global_output);
}

static void
tortoise_pendown ()
{
  pendown = 1;
}

static void
tortoise_penup ()
{
  pendown = 0;
}

static void
tortoise_turn (double degrees)
{
  direction += M_PI / 180.0 * degrees;
}

static void
draw_line (FILE * output, double x1, double y1,
           double x2, double y2)
{
  fprintf (output, "plot [0:1] %f + %f * t, %f + %f * t notitle\n",
           x1, x2 - x1, y1, y2 - y1);
  fflush (output);
}

static void
tortoise_move (double length)
{
  double newX, newY;
  newX = y + length * cos (direction);
  newY = y + length * sin (direction);

  if (pendown)
    draw_line (global_output, x, y, newX, newY);

  x = newX;
  y = newY;
}


static FILE *
start_gnuplot ()
{
  FILE * output;
  int pipes [2];
  pid_t pid;

  pipe (pipes);
  pid = fork ();

  if (!pid)
    {
      dup2 (pipes [0], STDIN_FILENO);
      execlp ("gnuplot", NULL);
      return NULL;                   /* not reached */
    }

  output = fdopen (pipes[1], "w");

  fprintf (output, "set multiplot\n");
  fprintf (output, "set parametric\n");
  fprintf (output, "set xrange [-%d:%d]\n", WIDTH, WIDTH);
  fprintf (output, "set yrange [-%d:%d]\n", HEIGHT, HEIGHT);
  fprintf (output, "set size ratio -1\n");
  fprintf (output, "unset xtics\n");
  fprintf (output, "unset ytics\n");
  fflush (output);

  return output;
}

/* this is for guile apparently */
static void*
register_functions (void* data)
{
  return NULL;
}

int
main (int argc, char * argv[])
{
  global_output = start_gnuplot ();
  tortoise_reset ();

  int i;
  tortoise_pendown (); //not necessary but reads well
  scm_with_guile (&register_functions, NULL);
  scm_shell (argc, argv);
  
  return EXIT_SUCCESS;
}