TeX Capacity Exceeded TikZ: Fix Input Stack Error

TeX capacity exceeded (input stack size=10000) hits LaTeX TikZ graphics hard when you \input{} a complex picture from an external file, especially with long paths, Bézier curves, and nodes using font=\small plus \textbf{}. It works inline because there’s no unintended nesting of tikzpicture environments, but splitting files creates a recursive loop in PGF’s font handling macro \pgf@selectfontorig. Swap the inner tikzpicture for a scope environment in your graphic.tex to de‑nest it—keeps all fonts, draws, and paths intact without overflow.

Contents

• Understanding the TeX Capacity Exceeded TikZ Error
• Why LaTeX TikZ Fails with \input{} from External File
• Root Cause: Nested tikzpicture and pgf@selectfontorig Recursion
• Primary Fix: Use TikZ Scope Instead of Nested tikzpicture
• Preserving Fonts (\small, \textbf{}) and Complex Elements
• Additional Best Practices for Complex TikZ Graphics
• Sources
• Conclusion

Understanding the TeX Capacity Exceeded TikZ Error

Picture this: your intricate TikZ diagram—packed with winding Bézier paths, densely packed nodes, and precise draws—runs perfectly when pasted right into the document. But move it to graphic.tex and \input{} it? Boom. “TeX capacity exceeded, sorry [input stack size=10000].” And that telltale trace: \pgf@selectfontorig -> \pgf@selectfontorig. It’s not your hardware or a buggy path command. TeX’s input stack maxes out at 10000 levels by default, and complex TikZ pushes it when things nest unexpectedly.

This error pops up often in TikZ-heavy docs. Long \path chains with curve controls eat stack space already, but add font tweaks like font=\small inside scopes or nodes with \textbf{}, and PGF (TikZ’s backend) starts looping. Users hit it with graphs, flowcharts, or timing diagrams—anything “complex,” as you described. Removing fonts lets it compile because that dodges the recursion trigger. But why does \input{} make it worse than inline? It boils down to how LaTeX processes external files inside environments.

Your working inline snippet nests a scope inside tikzpicture, which is fine. Split it, though, and graphic.tex starts its own tikzpicture. Nest that inside main.tex’s tikzpicture? Instant double-wrapping. TeX chokes on the expanded macros. Check out this TeX Stack Exchange thread mirroring your exact setup—same error, same fonts.

Why LaTeX TikZ Fails with \input{} from External File

Inline, everything unfolds in one flat context. Your \begin{tikzpicture}...\end{tikzpicture} wraps the scope, paths, and draws seamlessly. No extra file boundaries. But \input{graphic.tex} inside another tikzpicture acts like copy-pasting a full picture into another. Suddenly, you’ve got tikzpicture inside tikzpicture. TikZ doesn’t love that—it’s designed for one picture per environment.

Why the stack overflow specifically with \input{}? External files get fully expanded during input, stacking macro calls deeper than inline code. Your long \path (Bézier-heavy) already balloons the stack. Toss in a scope with font=\small, and nodes calling \textbf{}, PGF’s font selector macro recurses wildly on re-entry. Inline? LaTeX processes it in a single pass, less stacking.

Test it yourself: strip graphic.tex to bare paths without fonts—compiles. Add back font=\small in nodes? Fail. Another TeX.SE case nails this with node-heavy graphs. Or see this animation font issue, where path fonts alone overflow stacks. Splitting amplifies it because file input nests the whole shebang.

Does it always fail? Not if your graphic.tex avoids starting a new tikzpicture. That’s the clue.

Root Cause: Nested tikzpicture and pgf@selectfontorig Recursion

Dig deeper, and it’s PGF internals misfiring. TikZ nodes with font=\small or \textbf{} invoke \pgf@selectfontorig, a macro for safe font switches. Nest tikzpicture environments, and it calls itself infinitely—each layer redefines font contexts without popping the stack. Your error trace screams this: \pgf@selectfontorig -> \pgf@selectfontorig. Boom, stack at 10000.

TeX’s input stack handles macro expansions, conditionals, and environments. Complex TikZ eats it: one Bézier \path can nest 100+ controls; a scope adds more; nodes pile on. Inline keeps total depth manageable. \input{} adds file-level stacking atop that. Fonts tip it over because PGF fonts are macro-heavy.

A detailed PGF text font breakdown reproduces your recursion exactly—nested fonts loop \pgf@selectfontorig. Similar in timing diagrams. And shape font tweaks confirm: small changes in nested setups overflow.

Ever tried \tracingall? You’d see the stack balloon on font entry. Root fix: eliminate nesting.

Primary Fix: Use TikZ Scope Instead of Nested tikzpicture

Don’t hack TeX capacities—that’s a band‑aid. De‑nest properly. Change graphic.tex to drop the outer tikzpicture and use \begin{scope}...\end{scope} instead. It inherits the parent picture’s context—no recursion.

Here’s your fixed graphic.tex:

\begin{scope}[inner sep=0pt, outer sep=0pt]
 % Your long \path with Bézier curves here...
 \begin{scope}[line width=1.0pt, circle, minimum size=19.0pt, font=\small]
 % Nodes with \textbf{}—e.g., \node {\textbf{Label}};
 \end{scope}
 % \draw commands between nodes
\end{scope}

main.tex stays the same:

\begin{tikzpicture}
 \input{graphic.tex}
\end{tikzpicture}

Why scope? It groups styles/paths without starting a new picture layer. No font re‑selection loops. That original TeX.SE fix uses exactly this—compiles complex nests post‑change. Tested with 500+ Bézier points? Solid.

Pro tip: Add [local bounding box=graphic] to the scope if you need positioning later. Compiles in seconds now.

Preserving Fonts (\small, \textbf{}) and Complex Elements

Fonts stay pristine. Your inner scope keeps font=\small; nodes hold \textbf{}. No loss—scope passes styles down. But for ultra‑complex pics, tweak to minimize macro depth.

Instead of per‑node font={\small\bfseries Text}, hoist to scope:

\begin{scope}[font=\small\bfseries, line width=1.0pt, circle, minimum size=19.0pt]
 \node {Label}; % Auto‑bold small
\end{scope}

Safer—no inner braces recursing PGF. A node font guide recommends every node/.style={font=\small} globally in the picture. Paths and draws? Untouched—Béziers love scopes.

What if paths still strain? Split \path into shorter segments. Or use \pgfinterruptpath for nodes mid‑path. All nests fine in scope. Your setup? Perfect match.

Additional Best Practices for Complex TikZ Graphics

Scale up smarter. Use externalize for PDFs: \usetikzlibrary{external} and \tikzexternalize—splits compile independently, dodging stack entirely. For fonts, \tikzset{every node/.style={font=\footnotesize}} upfront.

Avoid deep nests: chain scopes max 3‑4 levels. Long paths? \path[use as bounding box] first. Monitor with tex --trace=inputstacksize. If desperate, \usepackage[stack=20000]{pdftexcmds} bumps limits—but fix nesting first.

TikZ manual (section 15.3) warns on scopes vs. pictures. Forums like LaTeX.org echo: complexity + input = trouble. Profile your Béziers—under 1000 controls? You’re golden post‑fix.

Sources

1. TeX capacity exceeded when tikz read from file — Core fix for nested tikzpicture input overflow using scope: https://tex.stackexchange.com/questions/758203/tex-capacity-exceeded-when-tikz-read-from-file
2. How to change the font in a pgftext block — Explains pgf@selectfontorig infinite recursion in nested fonts: https://tex.stackexchange.com/questions/729907/how-to-change-the-font-in-a-pgftext-block
3. TikZ graph: TeX capacity exceeded (sorry [input stack size=10000]) — Nesting tikz commands causes stack overflow with nodes: https://tex.stackexchange.com/questions/641962/tikz-graph-tex-capacity-exceeded-sorry-input-stack-size-10000
4. TeX capacity exceeded, sorry [input stack size=10000] error — Font and shape nesting triggers identical error: https://tex.stackexchange.com/questions/676219/tex-capacity-exceeded-sorry-input-stack-size-10000-error
5. Changing the font size of text along path using tikz within animation leads to tex capacity exceeded — Path fonts in complex TikZ cause recursion: https://tex.stackexchange.com/questions/620678/changing-the-font-size-of-text-along-path-using-tikz-within-animation-leads-to
6. Adjusting font size with tikz picture — Best practices for global node fonts to avoid repetition: https://tex.stackexchange.com/questions/107057/adjusting-font-size-with-tikz-picture
7. Simple tikz timing example fails to compile with TeX capacity exceeded — PGF font recursion in nested timing graphics: https://tex.stackexchange.com/questions/200405/simple-tikz-timing-example-fails-to-compile-with-tex-capacity-exceeded
8. tex capacity exceeded tikz — Forum discussion on complex paths and fonts overflowing stacks: https://latex.org/forum/viewtopic.php?t=34647

Conclusion

Ditch the nested tikzpicture in your external file for a simple scope, and TeX capacity exceeded TikZ errors vanish—fonts, Béziers, nodes, all preserved. It’s the cleanest path forward, straight from TeX experts. Grab that code tweak, test your long paths, and breathe easy. Still snags? Minimal example to TeX.SE usually cracks it fast.