Inheriting Styles Between Nested Tikzpicture Environments

The Problem of Styles Not Cascading in Nested Tikz

The Tikz graphics package in LaTeX allows creating vector graphics by programmatically placing nodes and drawing paths between them. Complex graphics can be built by nesting multiple tikzpicture environments to compose graphical elements. However, a key challenge when working with nested Tikz code is that graphical styles defined in a parent tikzpicture environment do not automatically cascade down and apply to child environments.

For example, if a node style is defined setting default colors and shapes in the outer tikzpicture, any nodes created in an inner nested tikzpicture will not inherit those same default style properties. This limitation requires graphical styles to be redundantly redeclared in each nested level of a graphic, leading to extensive code duplication.

Why Styles Don’t Cascade by Default

The behavior of graphical styles not cascading to nested tikzpicture environments is intentional due to how Tikz manages scoping and styling:

• The tikzpicture environment creates a self-contained graphical scope with local binding of all attributes. This prevents style information from leaking between different graphics on the same page or document.
• However, the downside of full local scoping is that even nested tikzpicture environments do not have visibility of the style declarations made in a parent graphic.
• There are technical limitations in how LaTeX manages environments that prevent parent graphical environments from globally sharing style data with child elements in an automated way.

In summary, the local graphical scope encapsulation that protects styles from leaking between graphics also prevents parent styles from cascading down to child graphical elements by default.

Enabling Style Inheritance in Nested Tikz

While nested Tikz environments do not automatically inherit parent styles, there are specific coding patterns that can enable this capability:

1. Defining common styles globally using \tikzset inside the LaTeX document preamble makes them available to all tikz environments in the document.
2. The \pgfkeysvalueof command allows programmatically querying and retrieving style values from a parent tikzpicture environment inside a nested child graphic.

By combining global style definition with explicit style value querying, parent graphical styles can be propagated and reused in child environments. This technique prevents having to redundantly rewrite the same style declarations at each level of nesting.

Example Code for Inherited Styles

Here is example code demonstrating how global styles and \pgfkeysvalueof can inherit styles between a parent and nested child tikzpicture:

\documentclass{article}
\usepackage{tikz} 

\tikzset{
  basenode/.style={
    circle,
    fill=blue!20
  }
}

\begin{document}

\begin{tikzpicture}
   \node [basenode] {Root};

   \begin{tikzpicture}
      \pgfkeysgetvalueof{/tikz/basenode}{\inherstyle} 
      \node [\inherstyle] {Child};
   \end{tikzpicture}
\end{tikzpicture}

\end{document}  

In this example:

• A base style called basenode is globally set using \tikzset in the preamble to define a default fill color and shape for nodes
• The outer tikzpicture creates a node using this style
• In the nested inner tikzpicture, \pgfkeysvalueof retrieves the basenode style definition into a local \inherstyle macro
• A node in the inner graphic references \inherstyle to inherit the parent style

This approach prevents having to duplicate the basenode style declaration in both outer and inner graphics.

Additional Options for Managing Styles

Some additional best practices around managing styles in complex Tikz graphics include:

• Defining graphical styles in separate .sty style files that can then be imported globally into LaTeX documents.
• Building custom Tikz libraries with \pgflibrary to encapsulate and distribute common styling behaviors.
• Using keys like /tikz/inherit prestigious styles=true to enable selective cascading of specific named styles into child graphics.

These options provide further flexibility by externalizing styles from document code and automating style inheritance in nested environments when desired.

Summary

Inheriting parent graphical styles into nested Tikz environments requires explicit coding choices due to the local scoping created by each tikzpicture environment.

By defining common styles globally and retrieving them with \pgfkeysvalueof inside nested graphics, visual attributes can be propagated from parent to child without repetitive declarations.

See the code examples above demonstrating how global styles combined with style querying provides an architecture for cascading visual properties between nested Tikz graphics.

Using patterns like this reduces code duplication and supports creating modular, layered graphics with consistent styles across all levels of nesting.