如何从外部化的 tikz 图片全局修改变量？

Question

是否可以从外部化的 tikz 图片中更新全局变量？

我希望全局修饰符（在本例中\tl_gput_right:Nn）能够超越 tikz 图片的范围。

以下是 MWE：

\documentclass{article}

\usepackage [utf8] {inputenc}
\usepackage {tikz}
\usepackage {xparse}

% Setup externalization.
\usetikzlibrary{external}
\tikzexternalize[prefix=images/]
\tikzset{png export/.style={external/system call/.add={}{; convert -density 300 "\image.pdf" "\image.png"}}}
\tikzset{png export}

% Declare global variable.
\ExplSyntaxOn
    \tl_clear_new:N \something
\ExplSyntaxOff

\begin {document}
    \ExplSyntaxOn

        % Draw a picture and update global variable.
        \begin{tikzpicture}
            \draw node {aaa};
            \tl_gput_right:Nn \something {AAA}
            \tl_log:N \something % Value is "AAA".
        \end{tikzpicture}

        % Print global variable afterwards.
        \tl_log:N \something % Value is "".

    \ExplSyntaxOff
\end {document}

我希望最后\tl_log:N显示的值AAA就像externalization部分被注释掉一样。

Answer 1

作为菲利佩·奥莱尼克根据评论中的建议，我最终将数据从tikzpicture环境写入外部文件，然后在tikzpicture结束时将其读回。

一种方法是：

\documentclass{article}

\usepackage [utf8] {inputenc}
\usepackage {tikz}
\usepackage {xparse}

% Setup externalization.
\usetikzlibrary{external}
\tikzexternalize[prefix=images/]
\tikzset{png export/.style={external/system call/.add={}{; convert -density 300 "\image.pdf" "\image.png"}}}
\tikzset{png export}

% Declare global variables.
\ExplSyntaxOn
    % Streams for reading and writing to file.
    \iow_new:N \output_stream
    \ior_new:N \input_stream

    \tl_clear_new:N \something
\ExplSyntaxOff

\begin {document}
    \ExplSyntaxOn

        % Draw a picture and update global variable.
        \begin{tikzpicture}
            \draw node {aaa};
            \tl_gput_right:Nn \something {AAA}
            \tl_log:N \something % Value is "AAA".

            % Store data in file to use it outside of tikzpicture.
            \iow_open:Nn \output_stream {stored_data}
            \iow_now:Nx \output_stream {\something} % You can generate \iow_now:NV variant instead of \iow_now:Nx
            \iow_close:N \output_stream
        \end{tikzpicture}

        % Read stored data from file.
        \ior_open:Nn \input_stream {stored_data}
        \ior_get:NN \input_stream \something
        \ior_close:N \input_stream

        % Print global variable afterwards.
        \tl_log:N \something % Value is now "AAA".

    \ExplSyntaxOff
\end {document}