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保存计算数字寄存器以供“let”操作体外部访问

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保存计算数字寄存器以供“let”操作体外部访问

PGF 手册第 14.15 节（第 150 页）描述了该let操作。在第 152 页（第一个示例）中，它应用于将坐标（元组值）保存到点寄存器p1，并p2使用该coordinate函数允许访问操作主体之外的计算坐标let。在我看来，应该可以以类似的方式保存和重用数字寄存器，但事实似乎并非如此。请参阅下面的建议代码。我想使用计算出的长度\n1作为子矩形的长度DATASET，但这在该语法的约束内似乎是不可能的。有什么想法吗？有解决方法吗？

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows, positioning, calc}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{5em}%
\begin{document}
\begin{tikzpicture}[auto]
  \tikzstyle{file} = [ellipse, rounded corners, minimum height=1em, minimum width=1em, align=center, draw]
  \tikzstyle{block} = [rectangle, rounded corners, minimum height=2em, minimum width=15em, align=center, draw]
  \node [block, minimum height=10em] (DB){\textbf{Database}};
  % Set coordinate points for sub-rectangles
  % See pg 420 of 2.10 PGF manual for anchors
  % 'let' is defined on pg 150 in Section 14.15 (The Let Operation)
  \path
  let
  \p1 = ($(DB.east)$),
  \p2 = ($(DB.west)$),
  \n1 = {veclen(\x1-\x2,\y1-\y2)/2}
  in
  coordinate(p1) at (\p1)
  coordinate(p2) at (\p2)
  %number(n1) at (\n1) % illustrative syntax
  ;
  % Use n1 for 'minimum width' instead of 2em
  \node [block, draw, minimum width=2em] (DATASET) at ($(DB.north)!2/7!(DB.south)$) {Dataset};
\end{tikzpicture}
\end{document}

答案1

您可以定义一个.code键，例如

\pgfkeys{/tikz/savenumber/.code 2 args={\global\edef#1{#2}}}

您可以使用

[savenumber={<macro to save to>}{<macro to save>}]

（注意方括号）位于 TikZ 路径的某处（包括操作期间let）。

你的例子看起来就像

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shapes,arrows, positioning, calc}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{5em}%

\pgfkeys{/tikz/savenumber/.code 2 args={\global\edef#1{#2}}}

\begin{document}
\begin{tikzpicture}[auto]
  \tikzstyle{file} = [ellipse, rounded corners, text width=12em, text height=3em, minimum height=1em, minimum width=1em, align=center, draw]
  \tikzstyle{block} = [rectangle, rounded corners, text width=12em, text height=3em, minimum height=2em, minimum width=15em, align=center, draw]
  \node [block, minimum height=10em] (DB){\textbf{Database}};
  % Set coordinate points for sub-rectangles
  % See pg 420 of 2.10 PGF manual for anchors
  % 'let' is defined on pg 150 in Section 14.15 (The Let Operation)
  \path
  let
  \p1 = ($(DB.east)$),
  \p2 = ($(DB.west)$),
  \n1 = {veclen(\x1-\x2,\y1-\y2)/2}
  in
  coordinate(p1) at (\p1)
  coordinate(p2) at (\p2)
  [savenumber={\n}{\n1}]
  ;
  % Use n1 for 'minimum width' instead of 2em
  \node [block, draw, minimum width=\n] (DATASET) at ($(DB.north)!2/7!(DB.south)$) {Dataset};
\end{tikzpicture}
\end{document}

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