void spSkipSpace(const char **pos)

  { while(**pos && isspace(**pos)) ++*pos; }

double spReadNum(const char **pos) {

  spSkipSpace(pos);

  char *end = "";

  double x = strtod(*pos, &end);

  *pos = end;

  return x;

}

void spTrack(const char *path, double *x, double *y) {

  double sx = *x, sy = *y;

  const char *c = path;

  spSkipSpace(&c);

  while(*c) {

    switch(*c++) {

    case 'M':

      sx = (*x = spReadNum(&c));

      sy = (*y = spReadNum(&c));

      break;

    case 'm':

      sx = (*x += spReadNum(&c));

      sy = (*y += spReadNum(&c));

      break;

    case 'C':

      spReadNum(&c);

      spReadNum(&c);

    case 'Q':

      spReadNum(&c);

      spReadNum(&c);

    case 'L':

      *x = spReadNum(&c);

      *y = spReadNum(&c);

      break;

    case 'c':

      spReadNum(&c);

      spReadNum(&c);

    case 'q':

      spReadNum(&c);

      spReadNum(&c);

    case 'l':

      *x += spReadNum(&c);

      *y += spReadNum(&c);

      break;

    case 'Z':

    case 'z':

      *x = sx;

      *y = sy;

      break;

    default:

      printf("unknown path command \'%c\'\n", *(c - 1));

    }

    spSkipSpace(&c);

  }

}