Fix broken diagrams in hidden containers (Reveal.js, tabs)#227
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drillan wants to merge 2 commits intomgaitan:masterfrom
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Fix broken diagrams in hidden containers (Reveal.js, tabs)#227drillan wants to merge 2 commits intomgaitan:masterfrom
drillan wants to merge 2 commits intomgaitan:masterfrom
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Mermaid's layout engine measures text dimensions via the DOM, which fails for elements hidden by a parent (e.g., Reveal.js non-active slides, sphinx-design unopened tabs). The layout calculation produces broken SVGs with near-zero viewBox dimensions. Use IntersectionObserver to defer rendering of hidden elements until they become visible. Visible elements render immediately as before. Fixes mgaitan#126 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
- Replace forEach+async with for...of and promise chain to serialize concurrent mermaid.run() calls from IntersectionObserver - Move data-mermaid-deferred removal to after successful render to prevent orphaned elements causing infinite polling - Add data-mermaid-render-failed attribute for failed elements and exclude them from completion checks - Add try/catch for visible element rendering - Warn explicitly when IntersectionObserver is unavailable - Add test for lazy rendering code presence Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This was referenced Feb 16, 2026
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Summary
IntersectionObserverto defer rendering of hidden Mermaid elements until they become visibledisplay: nonecontainers (e.g., Reveal.js non-active slides, sphinx-design unopened tabs)Problem
When
mermaid_output_format = "raw",mermaid.run()processes all.mermaidelements at page load. For elements hidden by a parent (display: none), the browser returns zero for all dimension measurements. This causes Mermaid's layout engine (dagre/ELK) to produce broken SVGs with near-zeroviewBoxdimensions, or throw"Could not find a suitable point for the distance"errors that manifest as "Syntax error in text".Affected contexts:
Approach
In the
runMermaid()function withindefault.js.j2:.mermaidelements into visible (offsetParent !== null || getClientRects().length > 0) and hiddenmermaid.run({ nodes: visible })for visible elements onlyIntersectionObserverfor hidden elements, rendering each when it becomes visiblemermaid.run()calls when multiple hidden elements become visible simultaneouslyTest plan
test_lazy_rendering_code_presentverifies IntersectionObserver and deferred rendering code is emittedFixes #126
🤖 Generated with Claude Code