function obj_display ( input_file_name )

%*****************************************************************************80

%

%% OBJ_DISPLAY displays the faces of a shape defined by an OBJ file.

%

%  Usage:

%

%    obj_display ( 'file.obj' )

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    27 September 2008

%

%  Author:

%

%    John Burkardt

%

  timestamp ( );

  fprintf ( 1, '\n' );

  fprintf ( 1, 'OBJ_DISPLAY\n' );

  fprintf ( 1, '  MATLAB version\n' );

  fprintf ( 1, '\n' );

  fprintf ( 1, '  Reads an object in an ASCII OBJ file.\n' );

  fprintf ( 1, '  Display it as a MATLAB shape.\n' );

%

%  If at least one command line argument, it's the input file name.

%

  if ( nargin < 1 )

    fprintf ( 1, '\n' );

    fprintf ( 1, 'OBJ_DISPLAY:\n' );

    input_file_name = input ( 'Enter the name of the input file:' );

  end

%

%  Get sizes.

%

  [ node_num, face_num, normal_num, order_max ] = obj_size ( input_file_name );

%

%  Print the sizes.

%

  obj_size_print ( input_file_name, node_num, face_num, normal_num, order_max );

%

%  Get the data.

%

  [ node_xyz, face_order, face_node ] = ...

    obj_read ( input_file_name, node_num, face_num, normal_num, order_max );

%

%  FACE_NODE may contain polygons of different orders.

%  To make the call to PATCH, we will assume all the polygons are the same order.

%  To do so, we'll simply "stutter" the first node in each face list.

%

  for face = 1 : face_num

    face_node(face_order(face)+1:order_max,face) = face_node(1,face);

  end

%

%  If any node index is still less than 1, set the whole face to 1's.

%  We're giving up on this presumably meaningless face, but we need to

%  do it in a way that keeps MATLAB happy!

%

  for face = 1 : face_num

    for i = 1 : order_max

      face_node(i,face) = max ( face_node(i,face), 1 );

    end

  end

%

%  Display the shape.

%

  handle = patch ( 'Vertices', node_xyz', 'Faces', face_node' );

  set ( handle, 'FaceColor', [0.5, 0.6, 0.8], 'EdgeColor', 'Black' );

  axis equal; 

  grid on;

  xlabel ( '--X axis--' )

  ylabel ( '--Y axis--' )

  zlabel ( '--Z axis--' )

%

%  The TITLE function will interpret underscores in the title.

%  We need to unescape such escape sequences!

%

  title_string = s_escape_tex ( input_file_name );

  title ( title_string )

%

%  Terminate.

%

  fprintf ( 1, '\n' );

  fprintf ( 1, 'OBJ_DISPLAY:\n' );

  fprintf ( 1, '  Normal end of execution.\n' );

  fprintf ( 1, '\n' );

  timestamp ( );

  return

end

function c = ch_cap ( c )

%*****************************************************************************80

%

%% CH_CAP capitalizes a single character.

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    22 November 2003

%

%  Author:

%

%    John Burkardt

%

%  Parameters:

%

%    Input, character C, the character to capitalize.

%

%    Output, character C, the capitalized character.

%

  if ( 'a' <= c && c <= 'z' )

    c = c + 'A' - 'a';

  end

  return

end

function truefalse = ch_eqi ( c1, c2 )

%*****************************************************************************80

%

%% CH_EQI is a case insensitive comparison of two characters for equality.

%

%  Example:

%

%    CH_EQI ( 'A', 'a' ) is TRUE.

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    28 July 2000

%

%  Author:

%

%    John Burkardt

%

%  Parameters:

%

%    Input, character C1, C2, the characters to compare.

%

%    Output, logical TRUEFALSE, is TRUE (1) if the characters are equal.

%

  FALSE = 0;

  TRUE = 1;

  if ( ch_cap ( c1 ) == ch_cap ( c2 ) )

    truefalse = TRUE;

  else

    truefalse = FALSE;

  end

  return

end

function value = ch_index ( s, c )

%*****************************************************************************80

%

%% CH_INDEX is the first occurrence of a character in a string.

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    01 May 2004

%

%  Author:

%

%    John Burkardt

%

%  Parameters:

%

%    Input, string S, the string to be searched.

%

%    Input, character C, the character to be searched for.

%

%    Output, integer VALUE, the location of the first occurrence of C 

%    in the string, or 0 if C does not occur.

%

  value = 0;

  for i = 1 : length ( s )

    if ( s(i:i) == c )

      value = i;

      return

    end

  end

  return

end

function value = ch_is_control ( ch )

%*****************************************************************************80

%

%% CH_IS_CONTROL is TRUE if a character is a control character.

%

%  Discussion:

%

%    A "control character" has ASCII code <= 31 or 127 <= ASCII code.

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    27 September 2008

%

%  Author:

%

%    John Burkardt

%

%  Parameters:

%

%    Input, character CH, the character to be tested.

%

%    Output, integer CH_IS_CONTROL, TRUE if the character is a control

%    character, and FALSE otherwise.

%

  if ( ch <= 31 || 127 <= ch )

    value = 1;

  else

    value = 0;

  end

  return

end

function truefalse = ch_is_digit ( c )

%*****************************************************************************80

%

% CH_IS_DIGIT returns TRUE if the character C is a digit.

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    11 December 2003

%

%  Author:

%

%    John Burkardt

%

%  Parameters:

%

%    Input, character C, a character.

%

%    Output, integer TRUEFALSE, is TRUE (1) if C is a digit, FALSE (0) otherwise.

%

  TRUE = 1;

  FALSE = 0;

  if ( '0' <= c && c <= '9' )

    truefalse = TRUE;

  else

    truefalse = FALSE;

  end

  return

end

function digit = ch_to_digit ( c )

%*****************************************************************************80

%

%% CH_TO_DIGIT returns the integer value of a base 10 digit.

%

%  Example:

%

%     C   DIGIT

%    ---  -----

%    '0'    0

%    '1'    1

%    ...  ...

%    '9'    9

%    ' '    0

%    'X'   -1

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    22 November 2003

%

%  Author:

%

%    John Burkardt

%

%  Parameters:

%

%    Input, character C, the decimal digit, '0' through '9' or blank

%    are legal.

%

%    Output, integer DIGIT, the corresponding integer value.  If C was

%    'illegal', then DIGIT is -1.

%

  if ( '0' <= c && c <= '9' )

    digit = c - '0';

  elseif ( c == ' ' )

    digit = 0;

  else

    digit = -1;

  end

  return

end

function [ node_xyz, face_order, face_node, normal_vector, vertex_normal ] = ...

  obj_read ( input_file_name, node_num, face_num, normal_num, order_max )

%*****************************************************************************80

%

%% OBJ_READ reads graphics information from a Wavefront OBJ file.

%

%  Discussion:

%

%    It is intended that the information read from the file can

%    either start a whole new graphics object, or simply be added

%    to a current graphics object via the '<<' command.

%

%    This is controlled by whether the input values have been zeroed

%    out or not.  This routine simply tacks on the information it

%    finds to the current graphics object.

%

%  Example:

%

%    #  magnolia.obj

%

%    v -3.269770 -39.572201 0.876128

%    v -3.263720 -39.507999 2.160890

%    ...

%    v 0.000000 -9.988540 0.000000

%    vn 1.0 0.0 0.0

%    ...

%    vn 0.0 1.0 0.0

%

%    f 8 9 11 10

%    f 12 13 15 14

%    ...

%    f 788 806 774

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    27 September 2008

%

%  Author:

%

%    John Burkardt

%

%  Parameters:

%

%    Input, string INPUT_FILE_NAME, the name of the input file.

%

%    Input, integer NODE_NUM, the number of points.

%

%    Input, integer FACE_NUM, the number of faces.

%

%    Input, integer NORMAL_NUM, the number of normal vectors.

%

%    Input, integer ORDER_MAX, the maximum number of vertices per face.

%

%    Output, real NODE_XYZ(3,NODE_NUM), the coordinates of points.

%

%    Output, integer FACE_ORDER(FACE_NUM), the number of vertices per face.

%

%    Output, integer FACE_NODE(ORDER_MAX,FACE_NUM), the nodes making faces.

%

%    Output, real NORMAL_VECTOR(3,NORMAL_NUM), normal vectors.

%

%    Output, integer VERTEX_NORMAL(ORDER_MAX,FACE_NUM), the indices of normal

%    vectors per vertex.

%

  face = 0;

  node = 0;

  normal = 0;

  text_num = 0;

  face_node = zeros ( order_max, face_num );

  face_order = zeros ( face_num, 1 );

  node_xyz = zeros ( 3, node_num );

  normal_vector = zeros ( 3, normal_num );

  vertex_normal = zeros ( order_max, face_num );

%

%  If no file input, try to get one from the user.

%

  if ( nargin < 1 )

    input_file_name = input ( 'Enter the name of the ASCII OBJ file.' );

    if ( isempty ( input_file_name ) )

      return

    end

  end

%

%  Open the file.

%

  input_file_unit = fopen ( input_file_name, 'r' );

  if ( input_file_unit < 0 )

    fprintf ( 1, '\n' );

    fprintf ( 1, 'OBJ_READ - Fatal error!\n' );

    fprintf ( 1, '  Could not open the file "%s".\n', input_file_name );

    error ( 'OBJ_READ - Fatal error!' );

  end

%

%  Read a line of text from the file.

%

  while ( 1 )

    text = fgetl ( input_file_unit );

    if ( text == -1 )

      break

    end

    text_num = text_num + 1;

%

%  Replace any control characters (in particular, TAB's) by blanks.

%

    s_control_blank ( text );

    done = 1;

    word_index = 0;

%

%  Read a word from the line.

%

    [ word, done ] = word_next_read ( text, done );

%

%  If no more words in this line, read a new line.

%

    if ( done )

      continue

    end

%

%  If this word begins with '#' or '$', then it's a comment.  Read a new line.

%

    if ( word(1) == '#' || word(1) == '$' )

      continue

    end

    word_index = word_index + 1;

    if ( word_index == 1 )

      word_one = word;

    end

%

%  BEVEL

%  Bevel interpolation.

%

    if ( s_eqi ( word_one, 'BEVEL' ) )

%

%  BMAT

%  Basis matrix.

%

    elseif ( s_eqi ( word_one, 'BMAT' ) )

%

%  C_INTERP

%  Color interpolation.

%

    elseif ( s_eqi ( word_one, 'C_INTERP' ) )

%

%  CON

%  Connectivity between free form surfaces.

%

    elseif ( s_eqi ( word_one, 'CON' ) )

%

%  CSTYPE

%  Curve or surface type.

%

    elseif ( s_eqi ( word_one, 'CSTYPE' ) )

%

%  CTECH

%  Curve approximation technique.

%

    elseif ( s_eqi ( word_one, 'CTECH' ) )

%

%  CURV

%  Curve.

%

    elseif ( s_eqi ( word_one, 'CURV' ) )

%

%  CURV2

%  2D curve.

%

    elseif ( s_eqi ( word_one, 'CURV2' ) )

%

%  D_INTERP

%  Dissolve interpolation.

%

    elseif ( s_eqi ( word_one, 'D_INTERP' ) )

%

%  DEG

%  Degree.

%

    elseif ( s_eqi ( word_one, 'DEG' ) )

%

%  END

%  End statement.

%

    elseif ( s_eqi ( word_one, 'END' ) )

%

%  F V1 V2 V3 ...

%    or

%  F V1/VT1/VN1 V2/VT2/VN2 ...

%    or

%  F V1//VN1 V2//VN2 ...

%

%  Face.

%  A face is defined by the vertices.

%  Optionally, slashes may be used to include the texture vertex

%  and vertex normal indices.

%

    elseif ( s_eqi ( word_one, 'F' ) )

      face = face + 1;

      vertex = 0;

      while ( 1 )

        [ word, done ] = word_next_read ( text, done );

        if ( done )

          break

        end

        vertex = vertex + 1;

        order_max = max ( order_max, vertex );

%

%  Locate the slash characters in the word, if any.

%

        i1 = ch_index ( word, '/' );

        if ( 0 < i1 )

          i2 = ch_index ( word(i1+1), '/' ) + i1;

        else

          i2 = 0;

        end

%

%  Read the vertex index.

%

        itemp = s_to_i4 ( word );

        face_node(vertex,face) = itemp;

        face_order(face) = face_order(face) + 1;

%

%  If there are two slashes, then read the data following the second one.

%

        if ( 0 < i2 )

          itemp = s_to_i4 ( word(i2+1) );

          vertex_normal(vertex,face) = itemp;

        end

      end

%

%  G

%  Group name.

%

    elseif ( s_eqi ( word_one, 'G' ) )

%

%  HOLE

%  Inner trimming loop.

%

    elseif ( s_eqi ( word_one, 'HOLE' ) )

%

%  L

%  A line, described by a sequence of vertex indices.

%  Are the vertex indices 0 based or 1 based?

%

    elseif ( s_eqi ( word_one, 'L' ) )

%

%  LOD

%  Level of detail.

%

    elseif ( s_eqi ( word_one, 'LOD' ) )

%

%  MG

%  Merging group.

%

    elseif ( s_eqi ( word_one, 'MG' ) )

%

%  MTLLIB

%  Material library.

%

    elseif ( s_eqi ( word_one, 'MTLLIB' ) )

%

%  O

%  Object name.

%

    elseif ( s_eqi ( word_one, 'O' ) )

%

%  P

%  Point.

%

    elseif ( s_eqi ( word_one, 'P' ) )

%

%  PARM

%  Parameter values.

%

    elseif ( s_eqi ( word_one, 'PARM' ) )

%

%  S

%  Smoothing group.

%

    elseif ( s_eqi ( word_one, 'S' ) )

%

%  SCRV

%  Special curve.

%

    elseif ( s_eqi ( word_one, 'SCRV' ) )

%

%  SHADOW_OBJ

%  Shadow casting.

%

    elseif ( s_eqi ( word_one, 'SHADOW_OBJ' ) )

%

%  SP

%  Special point.

%

    elseif ( s_eqi ( word_one, 'SP' ) )

%

%  STECH

%  Surface approximation technique.

%

    elseif ( s_eqi ( word_one, 'STECH' ) )

%

%  STEP

%  Stepsize.

%

    elseif ( s_eqi ( word_one, 'STEP' ) )

%

%  SURF

%  Surface.

%

    elseif ( s_eqi ( word_one, 'SURF' ) )

%

%  TRACE_OBJ

%  Ray tracing.

%

    elseif ( s_eqi ( word_one, 'TRACE_OBJ' ) )

%

%  TRIM

%  Outer trimming loop.

%

    elseif ( s_eqi ( word_one, 'TRIM' ) )

%

%  USEMTL

%  Material name.

%

    elseif ( s_eqi ( word_one, 'USEMTL' ) )

%

%  V X Y Z

%  Geometric vertex.

%

    elseif ( s_eqi ( word_one, 'V' ) )

      node = node + 1;

      for i = 1 : 3

        [ word, done ] = word_next_read ( text, done );

        temp = s_to_r8 ( word );

        node_xyz(i,node) = temp;

      end

%

%  VN

%  Vertex normals.

%

    elseif ( s_eqi ( word_one, 'VN' ) )

      normal = normal + 1;

      for i = 1 : 3

        [ word, done ] = word_next_read ( text, done );

        temp = s_to_r8 ( word );

        normal_vector(i,normal) = temp;

      end

%

%  VT

%  Vertex texture.

%

    elseif ( s_eqi ( word_one, 'VT' ) )

%

%  VP

%  Parameter space vertices.

%

    elseif ( s_eqi ( word_one, 'VP' ) )

%

%  Unrecognized keyword.

%

    else

    end

  end

  fclose ( input_file_unit );

  return

end

function [ node_num, face_num, normal_num, order_max ] = obj_size ( ...

  input_file_name )

%*****************************************************************************80

%

%% OBJ_SIZE determines sizes of graphics objects in an Alias OBJ file.

%

%  Discussion:

%

%    The only items of interest to this routine are vertices,

%    faces, and normal vectors.

%

%  Example:

%

%    #  magnolia.obj

%

%    v -3.269770 -39.572201 0.876128

%    v -3.263720 -39.507999 2.160890

%    ...

%    v 0.000000 -9.988540 0.000000

%

%    vn 1.0 0.0 0.0

%    ...

%    vn 0.0 1.0 0.0

%

%    f 8 9 11 10

%    f 12 13 15 14

%    ...

%    f 788 806 774

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    26 September 2008

%

%  Author:

%

%    John Burkardt

%

%  Parameters:

%

%    Input, string INPUT_FILE_NAME, the input file name.

%

%    Output, integer NODE_NUM, the number of points.

%

%    Output, integer FACE_NUM, the number of faces.

%

%    Output, integer NORMAL_NUM, the number of normal vectors.

%

%    Output, integer ORDER_MAX, the maximum face order.

%

  face_num = 0;

  node_num = 0;

  normal_num = 0;

  order_max = 0;

  text_num = 0;

%

%  If no file input, try to get one from the user.

%

  if ( nargin < 1 )

    input_file_name = input ( 'Enter the name of the ASCII OBJ file.' );

    if ( isempty ( input_file_name ) )

      return

    end

  end

%

%  Open the file.

%

  input_file_unit = fopen ( input_file_name, 'r' );

  if ( input_file_unit < 0 )

    fprintf ( 1, '\n' );

    fprintf ( 1, 'OBJ_SIZE - Fatal error!\n' );

    fprintf ( 1, '  Could not open the file "%s".\n', input_file_name );

    error ( 'OBJ_SIZE - Fatal error!' );

  end

%

%  Read a line of text from the file.

%

  while ( 1 )

    text = fgetl ( input_file_unit );

    if ( text == -1 )

      break

    end

    text_num = text_num + 1;

%

%  Replace any control characters (in particular, TABs) by blanks.

%

    s_control_blank ( text );

    done = 1;

    word_index = 0;

%

%  Read a word from the line.

%

    [ word, done ] = word_next_read ( text, done );

%

%  If no more words in this line, read a new line.

%

    if ( done )

      continue

    end

%

%  If this word begins with '#' or '$', then it is a comment.  Read a new line.

%

    if ( word(1) == '#' || word(1) == '$' )

      continue

    end

    word_index = word_index + 1;

    if ( word_index == 1 )

      word_one = word;

    end

%

%  F V1 V2 V3 ...

%    or

%  F V1/VT1/VN1 V2/VT2/VN2 ...

%    or

%  F V1//VN1 V2//VN2 ...

%

%  Face.

%  A face is defined by the vertices.

%  Optionally, slashes may be used to include the texture vertex

%  and vertex normal indices.

%

    if ( s_eqi ( word_one, 'F' ) )

      face_num = face_num + 1;

      vertex = 0;

      while ( 1 )

        [ word, done ] = word_next_read ( text, done );

        if ( done )

          break

        end

        vertex = vertex + 1;

        order_max = max ( order_max, vertex );

%

%  Locate the slash characters in the word, if any.

%

        i1 = ch_index ( word, '/' );

        if ( 0 < i1 )

          i2 = ch_index ( word(i1+1), '/' ) + i1;

        else

          i2 = 0;

        end

%

%  Read the vertex index.

%

        s_to_i4 ( word );

%

%  If there are two slashes, then read the data following the second one.

%

        if ( 0 < i2 )

          s_to_i4 ( word(i2+1) );

        end

      end

%

%  V X Y Z W

%  Geometric vertex.

%

    elseif ( s_eqi ( word_one, 'V' ) )

      node_num = node_num + 1;

      continue

%

%  VN

%  Vertex normals.

%

    elseif ( s_eqi ( word_one, 'VN' ) )

      normal_num = normal_num + 1;

      continue

    end

  end

  fclose ( input_file_unit );

  return

end

function obj_size_print ( input_file_name, node_num, face_num, normal_num, ...

  order_max )

%*****************************************************************************80

%

%% OBJ_SIZE_PRINT prints sizes associated with an OBJ file.

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    26 September 2008

%

%  Author:

%

%    John Burkardt

%

%  Parameters:

%

%    Input, string INPUT_FILE_NAME, the name of the input file.

%

%    Input, integer NODE_NUM, the number of vertices defined.

%

%    Input, integer FACE_NUM, the number of faces defined.

%

%    Input, integer NORMAL_NUM, the number of normal vectors defined.

%

%    Input, integer ORDER_MAX, the maximum number of vertices per face.

%

  fprintf ( 1, '\n' );

  fprintf ( 1, '  Object sizes for OBJ file "%s":\n', input_file_name );

  fprintf ( 1, '\n' );

  fprintf ( 1, '  Nodes              = %d\n', node_num );

  fprintf ( 1, '  Faces              = %d\n', face_num );

  fprintf ( 1, '  Maximum face order = %d\n', order_max );

  fprintf ( 1, '  Normal vectors     = %d\n', normal_num );

  return

end

function s = s_control_blank ( s )

%*****************************************************************************80

%

%% S_CONTROL_BLANK replaces control characters with blanks.

%

%  Discussion:

%

%    A "control character" has ASCII code <= 31 or 127 <= ASCII code.

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    27 September 2008

%

%  Author:

%

%    John Burkardt

%

%  Parameters:

%

%    Input/output, string S, the string to be transformed.

%

  s_length = s_len_trim ( s );

  for i = 1 : s_length

    if ( ch_is_control ( s(i) ) )

      s(i) = ' ';

    end

  end

  return

end

function value = s_eqi ( s1, s2 )

%*****************************************************************************80

%

%% S_EQI is a case insensitive comparison of two strings for equality.

%

%  Example:

%

%    S_EQI ( 'Anjana', 'ANJANA' ) is TRUE.

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    30 April 2004

%

%  Author:

%

%    John Burkardt

%

%  Parameters:

%

%    Input, string S1, S2, the strings to compare.

%

%    Output, logical VALUE, is TRUE if the strings are equal.

%

  FALSE = 0;

  TRUE = 1;

  len1 = length ( s1 );

  len2 = length ( s2 );

  lenc = min ( len1, len2 );

  for i = 1 : lenc

    c1 = ch_cap ( s1(i) );

    c2 = ch_cap ( s2(i) );

    if ( c1 ~= c2 )

      value = FALSE;

      return

    end

  end

  for i = lenc + 1 : len1

    if ( s1(i) ~= ' ' )

      value = FALSE;

      return

    end

  end

  for i = lenc + 1 : len2

    if ( s2(i) ~= ' ' )

      value = FALSE;

      return

    end

  end

  value = TRUE;

  return

end

function s2 = s_escape_tex ( s1 )

%*****************************************************************************80

%

%% S_ESCAPE_TEX de-escapes TeX escape sequences.

%

%  Discussion:

%

%    In particular, every occurrence of the characters '\', '_',

%    '^', '{' and '}' will be replaced by '\\', '\_', '\^',

%    '\{' and '\}'.  A TeX interpreter, on seeing these character

%    strings, is then likely to return the original characters.

%

%  Licensing:

%

%    This code is distributed under the GNU LGPL license.

%

%  Modified:

%

%    19 January 2007

%

%  Author:

%

%    John Burkardt

%

%  Parameters:

%

%    Input, string S1, the string to be de-escaped.

%

%    Output, string S2, a copy of the string, modified to avoid TeX escapes.

%

  s1_length = length ( s1 );

  s1_pos = 0;

  s2_pos = 0;

  s2 = [];

  while ( s1_pos < s1_length )

    s1_pos = s1_pos + 1;

    if ( s1(s1_pos) == '\' || ...

         s1(s1_pos) == '_' || ...

         s1(s1_pos) == '^' || ...

         s1(s1_pos) == '{' || ...

         s1(s1_pos) == '}' )

      s2_pos = s2_pos + 1;

      s2 = strcat ( s2, '\' );

    end

    s2_pos = s2_pos + 1;

    s2 = strcat ( s2, s1(s1_pos) );

  end

  return

end

function len = s_len_trim ( s )