I've written a prototype LaTeX package and associated viewing framework to allow LaTeX documents to be viewed in an environment that allows for interaction with figures. The figure might have points that can be dragged around, accept numerical inputs from the keyboard, make use of various GUI widgets, etc. The intent is for LaTeX to produce a PDF as it normally does, but allow the PDF, together with some additional files, to be loaded into a special viewer that replaces all the static figures of the PDF with interactive figures. Visibly, the two versions, static and interactive, are to be identical in every way other than being interactive or static. I have proof-of-concept using a web-browser as the platform for viewing and interaction. There's also a less developed version for Java, but that seems less useful, so it was abandoned.

The LaTeX end of the framework is shown below, and it works, with one remaining problem. As discussed in Setting the height of a tikzpicture using latex3, the area of the figures isn't stable. The answer provided there works for the MWE given, but not in the full context.

To recap, the intfig environment takes a file name (without a .tikz suffix), and the height that the figure must have. The environment looks for the given .tikz file. If the file exists, it is loaded; if it does not exist, then a box is displayed with a "not available" message. If the file doesn't exist and is not loaded then the figure has one height; if the file is available, then the figure seems to be one line of text taller than expected, as though there is an extra \par following the figure.

I am hoping for specific help on the problem of figure placement, and general suggestions for improvement since I am far from an expert on LaTeX3.

There are some additional remarks about how the system works in the code below.


% To precisely locate figures within a document.

% To treat environment verbatim.


% The inner and outer margin widths. There should be a way to
% determine these programmatically instead of having the user provide
% their best estimate, but I don't know how.
\dim_new:N \l_intfig_innermargin_dim
\dim_new:N \l_intfig_outermargin_dim

\dim_set:Nn \l_intfig_innermargin_dim { 0 pt }
\dim_set:Nn \l_intfig_outermargin_dim { 0 pt }

\NewDocumentCommand\SetInnerMargin { m }
  \dim_set:Nn \l_intfig_innermargin_dim { #1 }

\NewDocumentCommand\SetOuterMargin { m }
  \dim_set:Nn \l_intfig_outermargin_dim { #1 }

% The figures file is open throughout the run.
\iow_new:N \g_figurefile_iow
\iow_open:Nn \g_figurefile_iow { figures.aux }

% Name for the figure, as given by the user.
\str_new:N \l_intfig_figname_str

% Manditory height given by the user.
\dim_new:N \l_intfig_height_dim

% Optional height given by the user (if the interactive height differs.
\dim_new:N \l_intfig_interactiveHeight_dim

% Scratch values used for calculation of figure position.
\tl_new:N \l_intfig_tempa_tl
\tl_new:N \l_intfig_tempb_tl
\tl_new:N \l_intfig_tempc_tl

% And several booleans.
\bool_new:N \l_intfig_hasintht_bool
\bool_new:N \l_intfig_external_bool
\bool_new:N \l_intfig_nostatic_bool
\bool_new:N \l_intfig_done_bool

% This is for the figures file: the position of the figure on the page.
\dim_new:N \l_intfig_pagepos_dim

% I don't really understand the whole concept of these "variants."
\cs_generate_variant:Nn \file_if_exist:nTF {V}
\cs_generate_variant:Nn \file_input:n {V}

\NewDocumentEnvironment{intfig} { > { \SplitArgument { 1 } { , } } m!o }
  % Not sure if this is needed. Are there any local variables at all?

  % Parse manditory arguments.
  \intfig_manargs #1

  % The optional arguments.
  \bool_set_false:N \l_intfig_hasintht_bool
  \bool_set_false:N \l_intfig_external_bool
  \bool_set_false:N \l_intfig_nostatic_bool
  \bool_set_false:N \l_intfig_done_bool
  \tl_if_blank:nTF { #2 } {} {
    \clist_set:Nn \l_intfig_optclist_clist { #2 }
    \intfig_optargs { } 

  % Prepare the data for the figures file.
  % The page number, obtained from a previous run.
  \str_set:Nx \l_intfig_filespec_str { 
    \use:c { zref@extractdefault } { \l_intfig_figname_str -pageno} { abspage } { 0 }

  % The inner and outer margins.
  \str_put_right:Nx \l_intfig_filespec_str { ~ \dim_to_decimal_in_bp:n \l_intfig_innermargin_dim }
  \str_put_right:Nx \l_intfig_filespec_str { ~ \dim_to_decimal_in_bp:n \l_intfig_outermargin_dim }

  % And the text width.
  \str_put_right:Nx \l_intfig_filespec_str { ~ \dim_to_decimal_in_bp:n \textwidth }

  % Calculation of figure location, taking into account the
  % possibility that the figure has been bumped to the next page.
  % Take the location of the bottom edge and subract the figure height.
  \tl_set:Nn \l_intfig_tempa_tl { \zposy { \l_intfig_figname_str } }
  % Convert the figure height to sp.
  \tl_set:Nn \l_intfig_tempb_tl { \dim_to_decimal_in_sp:n{ \l_intfig_height_dim } }
  % Add 
  \tl_set:Nn \l_intfig_tempc_tl { \int_eval:n { \l_intfig_tempa_tl + \l_intfig_tempb_tl } }
  % Convert to a dim
  \dim_set:Nn \l_intfig_pagepos_dim { \l_intfig_tempc_tl sp }
  % And (whew!) write it out, in bp.
  \str_put_right:Nx \l_intfig_filespec_str { ~ \dim_to_decimal_in_bp:n \l_intfig_pagepos_dim }

  % The latex height of the figure (in bp)
  \str_put_right:Nx \l_intfig_filespec_str { ~ \dim_to_decimal_in_bp:n \l_intfig_height_dim }

  % The interactive height, which may be the latex height repeated.
  \bool_if:NTF \l_intfig_hasintht_bool
  { \str_put_right:Nx \l_intfig_filespec_str { ~ \dim_to_decimal_in_bp:n \l_intfig_interactiveHeight_dim }
  } % else
    \str_put_right:Nx \l_intfig_filespec_str { ~ \dim_to_decimal_in_bp:n \l_intfig_height_dim }

  % The figure name.
  \str_put_right:Nx \l_intfig_filespec_str { ~ \l_intfig_figname_str }

  % And a boolean
  \bool_if:NTF \l_intfig_done_bool
    \str_put_right:Nx \l_intfig_filespec_str { ~ true }
    \str_put_right:Nx \l_intfig_filespec_str { ~ false }

  % String is ready. Write out the line.
  \iow_now:Nx \g_figurefile_iow { \l_intfig_filespec_str }
  % Based on the optional arguments, write the body of the environment to a
  % file, and/or read a tikz file to replace the current body (which may  be
  % blank). Set two booleans to indicate whether to do these two things.
  \bool_set_false:N \l_intfig_writebody_bool
  \bool_set_false:N \l_intfig_readtikz_bool

  \bool_if:NTF \l_intfig_done_bool
    \bool_if:NTF \l_intfig_nostatic_bool {} {
      \bool_set_true:N \l_intfig_readtikz_bool
    \bool_if:NTF \l_intfig_external_bool
      \bool_if:NTF \l_intfig_nostatic_bool {}
        { \bool_set_true:N \l_intfig_readtikz_bool }
      \bool_set_true:N \l_intfig_writebody_bool
      \bool_if:NTF \l_intfig_nostatic_bool  { }
        \bool_set_true:N \l_intfig_readtikz_bool

  % The output file name needs an extra ".fjs" on the end.
  % Apparently, on Windows, you can't use a suffix for executable
  % types. No .js, no .py, .pl, etc.
  \str_set_eq:NN \l_intfig_jinfile_str \l_intfig_figname_str
  \str_put_right:Nn \l_intfig_jinfile_str { .fjs }
  % Whether to add an additional EOL to the output file depends on
  % whether there were any optional arguments. This is mysterious to me.
  \IfValueTF {#2}
    { \xsim_file_write_start:nn { \c_true_bool } }
    { \xsim_file_write_start:nn { \c_false_bool } }
    { \l_intfig_jinfile_str }
  % Post environment commands.

  % Stop writing the body since it's done.

  % And replace the current body with an external tikz file.
  \str_set_eq:NN \l_intfig_tikzfile_str \l_intfig_figname_str
  \str_put_right:Nn \l_intfig_tikzfile_str { .tikz }
  \file_if_exist:VTF \l_intfig_tikzfile_str {
    % Load the tikz file here.
    \file_input:V \l_intfig_tikzfile_str
    % No tikz file exists. Display a big empty box.
      \useasboundingbox (0pt,0pt) rectangle (\textwidth,\l_intfig_height_dim);
      \draw[dashed] (0pt,0pt) rectangle ( \textwidth,\l_intfig_height_dim);
      \node at (\textwidth / 2,\l_intfig_height_dim / 2) {The\ drawing\ is\ not\ available\ to\ load.};
      \draw (5pt,5pt) rectangle ( \textwidth - 5,\l_intfig_height_dim - 5);
  % Note values for the next run.
  \zsaveposy { \l_intfig_figname_str }
  \zlabel{ \l_intfig_figname_str -pageno}

% Parser for manditory arguments.
\NewDocumentCommand{\intfig_manargs}{ m m }
  \str_set:Nn \l_intfig_figname_str { #1 }
  \dim_set:Nn \l_intfig_height_dim { #2 }

% Parser for optional arguments.
\NewDocumentCommand{\intfig_optargs} { }
  \seq_set_from_clist:NN \l_intfig_optseq_seq { \l_intfig_optclist_clist }
  \seq_get_left:NN \l_intfig_optseq_seq \l_intfig_firstvalue_tl
  \intfig_if_length:VTF \l_intfig_firstvalue_tl 
    \dim_set:Nn \l_intfig_interactiveHeight_dim \l_intfig_firstvalue_tl
    \bool_set_true:N \l_intfig_hasintht_bool
    % If it's not a dimension, then ignore it.

  % Check whether each possible boolean flag has been set.
  \clist_if_in:NnTF \l_intfig_optclist_clist { external } 
    \bool_set_true:N \l_intfig_external_bool
  \clist_if_in:NnTF \l_intfig_optclist_clist { nostatic } 
    \bool_set_true:N \l_intfig_nostatic_bool
  \clist_if_in:NnTF \l_intfig_optclist_clist { done } 
    \bool_set_true:N \l_intfig_done_bool

% Regex to determine whether an input is a dimension. I can't say that
% I really understand what's going on here, other than a bit of copy
% and paste and help from stack overflow.
\prg_new_protected_conditional:Nnn \intfig_if_length:n { T, F, TF }
  % Note that I only allow positive values.
   { \A [+]? ((\d+(\.\d*)?)|(\.\d+)) \s* (pt|pc|in|bp|cm|mm|dd|cc|sp|ex|em) \Z} 
   { #1 } % test string
   { \prg_return_true: }
   { \prg_return_false: }
\prg_generate_conditional_variant:Nnn \intfig_if_length:n { V } { T, F, TF }




\\ Code for an external framework goes here.
\\ This is saved to bezier.fjs to be loaded by the framework.
\\ It could be JavaScript or Java (or whatever the framework is written to expect).

Here, {\tt bezier} is the ``name'' of the figure, and {\tt 200bp} is
the figure's height. The {\tt intfig} environment writes the body of
the environment out to a file ({\tt bezier.fjs} in this case). Then it
looks for a file, {\tt bezier.tikz}. If that file exists, it is
inserted; if it doesn't exist, then a ``not available'' message
appears in a figure of the given height.

In addition to swapping the body, {\tt intfig} writes information
about the page layout to {\tt figures.aux}: the page on which the
figure appears, together with its position on the page, the margin
sizes, text width, vertical location of the figure on the page, figure
height, figure name, and certain boolean values.

The interactive viewer might produce the following
as {\tt bezier.tikz}. If this file exists, it will be loaded as the
body of the {\tt intfig} above.

\useasboundingbox (0bp,0bp) rectangle (343.71109bp,200bp);
\draw[line width=4bp] (63.56039999999999bp, 27.39158999999995bp) -- (23.560399999999987bp, 57.39158999999995bp) -- (96.56039999999999bp, 121.39158999999995bp) -- (199.5604bp, 79.39158999999995bp) ;
\draw[line width=4bp] (63.56039999999999bp, 27.39158999999995bp) .. controls (23.560399999999987bp, 57.39158999999995bp) and (96.56039999999999bp, 121.39158999999995bp) .. (199.5604bp, 79.39158999999995bp);
\fill (63.56039999999999bp,27.39158999999995bp) ellipse [x radius=3bp,y radius =3bp];
\fill (23.560399999999987bp,57.39158999999995bp) ellipse [x radius=3bp,y radius =3bp];
\fill (96.56039999999999bp,121.39158999999995bp) ellipse [x radius=3bp,y radius =3bp];
\fill (199.5604bp,79.39158999999995bp) ellipse [x radius=3bp,y radius =3bp];

  • 1
    your bezier.tikz ends with a space and so allows a line break before the following \zsaveposy and \zlabel and that creates a line. Use \par\zrefsaveposy Commented May 5, 2022 at 15:35
  • What the heck! That does fix it, although it's a mystery how adding a \par gets rid of the \par I don't want. Many many thanks. Commented May 5, 2022 at 15:52

1 Answer 1


\label commands are whatsits and can affect spacing. E.g. a simple variant of your problem is

\rule{\textwidth}{1pt} \zsavepos{A}% space allows line break





enter image description here

If you put a \par before the \zsavepos you ensure that both cases behave identical. The alternative is to ensure that there are no unwanted spaces.

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