Tikz Styles: Local Vs Global Definitions And Why It Matters
The Problem of Scattered Style Definitions
When creating graphics with TikZ, styles play a key role in configuring visual attributes like colors, line widths, node shapes, and more. However, without careful planning, style definitions can easily become scattered across multiple locations in a document.
Defining styles locally within each tikzpicture environment seems convenient at first. But this leads to duplicated code and inconsistent styling over time. If a style needs updating, changes must be propagated manually to each instance.
Likewise, putting all style definitions in the document preamble avoids duplication but reduces flexibility. Local styles overriding global defaults is not possible.
So neither strictly local nor strictly global definitions are optimal. Instead, a hybrid approach allows global styles to define document-wide defaults while local styles customize them for individual diagrams.
Global vs Local Definitions in TikZ
In TikZ, styles can be defined globally for the whole document using \tikzset, or locally within a tikzpicture using \tikzstyle. Each approach has tradeoffs.
Global styles centralize common formatting in one location. This avoids repetitive declarations in each graphic. Changes made to global styles automatically apply everywhere. However, global styles also enforce document-wide conventions that cannot be overridden locally.
Local styles allow customization within a specific tikzpicture. For example, certain nodes can use special formatting that diverges from the defaults. Local styles also avoid namespace collisions since they are self-contained. But this forces duplication for commonly-used styles.
Examples of Global and Local TikZ Style Definitions
Here is an example with only global style definitions in the preamble:
\tikzset{
mynode/.style={
circle,
minimum size=1cm,
draw=blue,
fill=red!30
}
}
This defines a style called mynode with fixed formatting. All nodes using that style document-wide will have the same blue outline, red fill, and circular shape.
In contrast, here is an example using only local styles:
\begin{tikzpicture}
\tikzstyle{mynode}=[circle,draw=blue,fill=red!30,minimum size=1cm]
\node[mynode] {My Node};
\end{tikzpicture}
Now the mynode style is restricted to this specific tikzpicture. But if we wanted to reuse it, the definition would have to be duplicated in other graphics as well.
Recommendations for Organizing TikZ Styles
An effective workflow uses a mix of thoughtfully-placed global and local styles. Here are some key recommendations:
- Globally define a theme file with document-wide stylistic defaults. This handles all the core styles needed for consistency.
- For complex or reusable graphics, define special-purpose local styles overriding only what is necessary. Avoid entirely local styles to encourage reuse.
- Use global styles to configure stylistic conventions and base attributes like colors, stroke width, basic shapes, etc.
- Use local styles as exceptions where specialized local control is needed.
When to Use Global vs Local Definitions
There are no strict rules dictating when a style must be global or local. However, here are some best practices:
- If a style will be reused frequently document-wide, define it globally to avoid duplication.
- If a style is specific to a particular diagram, define it locally within that tikzpicture.
- Use local styles to modify or extend global defaults as needed for individual cases.
- Restrict local definitions only to exceptions, keep them globally consistent otherwise.
With experience, a natural balance emerges. The global theme file handlesgenerators most styling while special cases are managed locally as needed.
Managing Scope and Inheritance with TikZ Styles
Understanding scope and inheritance behavior is key to effectively managing styles. Consider the following example:
\tikzset{
group 1/.style={
basic style,
draw=blue
}
}
\begin{tikzpicture}
\tikzset{
basic style/.style={
circle,
minimum size=1cm
}
}
\node [group 1] {Node 1};
\end{tikzpicture}
Here group 1 inherits from basic style due to the ordering. The node will be blue since group 1 overrides the inherited black stroke color. Scope is also important - basic style is unavailable outside the tikzpicture while group 1 is global.
In general, inheritance flows from the global theme file, to local tikzpicture definitions, finally to individual node styles. Local styles can augment globals but not vice versa. Managing this capability appropriately is key.
Debugging Issues Caused by Style Scope
Style scoping issues can sometimes lead to cryptic TikZ errors. For example, this modification of the previous example generates an error:
\tikzset{
group 1/.style={
basic style,
draw=blue
}
}
\begin{tikzpicture}
\node [group 1] {Node 1};
\tikzset{
basic style/.style={
circle,
minimum size=1cm
}
}
\end{tikzpicture}
When group 1 is applied, basic style is still undefined leading to a reference error. Swapping the ordering fixes it, but debugging such issues can be tricky.
To avoid such problems, adopt consistent conventions. Styles should normally flow from global theme, to local tikzpicture, to individual nodes. Jumping across scopes leads to problems.
Best Practices for Consistent and Maintainable Documents
Consistent use of global vs local styles, along with other conventions, greatly improves maintainability:
- Define a global theme file early and reference it across all TikZ figures.
- Use global theme for common attributess like stroke color, fill color, text font, arrowheads, etc.
- Restrict local styles to a supporting role, not as primary definitions.
- Scope local styles within tikzpicture when possible to contain complexity.
- Utilize TikZ's style inheritance mechanism to layer on modifications.
- Standardize constructs like arrow tips, node shapes, and color palettes.
Adopting such practices ensures clean compartmentalization between global defaults, local adaptations, and element-specific customizations. This promotes understandability and maintainability within sizable TikZ documents.
