#include <stdio.h>
#include <stdlib.h>
#include <gtk/gtk.h>
#include <glib.h>
#include <math.h>
#define INTERVAL 100

typedef struct
{
  gint last_x, last_y;
  gdouble distance;
} MotionRecord;

gdouble distance (gint dx, gint dy)
{
  static gboolean initialized = FALSE;
  static gdouble dx_mm, dy_mm;
  if (!initialized)
    {
      gdouble width_meter, width_pixel, height_meter, height_pixel;
      GdkScreen *screen = gdk_screen_get_default ();
      width_meter = (gdouble)gdk_screen_get_width_mm (screen) / 1000;
      width_pixel = gdk_screen_get_width (screen);
      height_meter = (gdouble)gdk_screen_get_height_mm (screen) / 1000;
      height_pixel = gdk_screen_get_height (screen);

      dx_mm = (gdouble)width_meter / width_pixel;
      dy_mm = (gdouble)height_meter / height_pixel;
      initialized = TRUE;
    }

  return sqrt (pow (dx_mm*dx, 2) + pow (dy_mm*dy, 2));
}

gboolean record_motion (gpointer data)
{
  static gboolean initialized = FALSE;
  MotionRecord *record = (MotionRecord *)data;
  GdkWindow *root_window;
  gint x, y;

  root_window = gdk_screen_get_root_window (gdk_screen_get_default ());
  gdk_window_get_pointer (root_window, &x, &y, NULL);

  if (initialized)
    {
      gint dx, dy;
      dx = record->last_x - x;
      dy = record->last_y - y;
      record->distance += distance (dx, dy);
    }
  else
    initialized = TRUE;

  record->last_x = x;
  record->last_y = y;
  g_print ("distance: %.2fm\n", record->distance);
  return TRUE;
}

int main (int argc, char **argv)
{
  MotionRecord record = {0};

  gtk_init (&argc, &argv);
  g_timeout_add (INTERVAL, record_motion, &record);
  gtk_main ();

  return EXIT_SUCCESS;
}