Fix controls rendering in StrictMode with R3F Canvas

[Copilot]

Fix Controls rendering in StrictMode inside R3F Canvas

Problem: Controls added from components inside @react-three/fiber Canvas do not render correctly when React StrictMode is enabled. The issue is related to CSS height calculation that happens prematurely.

Root Cause: The useToggle hook in /packages/leva/src/hooks/useToggle.ts uses getBoundingClientRect() to calculate content height for collapse/expand animations. In React 18+ StrictMode, effects run twice during initial mount (mount → cleanup → remount).

The original implementation used a firstRender boolean ref that would be set to false on the first effect run. This caused the second effect run (during StrictMode's remount) to execute the height calculation logic prematurely, before the R3F Canvas content was fully laid out, resulting in incorrect height values.

Solution: Replaced the firstRender boolean ref with a prevToggledRef that tracks the previous toggle state:

• When prevToggledRef.current is null (initial render), skip animation logic entirely
• When prevToggledRef.current equals the current toggled value, skip animation (handles StrictMode's double-invocation)
• Only when toggled actually changes from the previous value, run the height calculation and animation

This ensures:

1. Initial render with toggled=true: No height is calculated/set, wrapper uses natural height ✅
2. Initial render with toggled=false: useLayoutEffect sets height to 0 (collapsed state) ✅
3. User toggles: Height is properly calculated and animated ✅
4. StrictMode's double-invocation: Second effect run is correctly skipped ✅

Changes Made:

• [x] Analyze the useToggle hook's height calculation logic
• [x] Fix the height calculation to work correctly with StrictMode double-invocation
• [x] Ensure the fix handles both initial render and toggle animations properly
• [x] Address code review feedback (remove duplicate assignment, fix comment)
• [x] Run security checks (CodeQL - no issues found)
• [x] Remove accidentally added yarn.lock file
• [x] Add R3F Canvas reproduction story with actual @react-three/fiber usage
• [x] Add @react-three/fiber and three as dev dependencies for the reproduction story

Testing: The fix is minimal and surgical, changing only the logic that determines when to run the animation. It maintains backward compatibility with existing behavior while properly handling StrictMode's double-invocation pattern. The change ensures controls render correctly in both development (with StrictMode) and production environments, particularly when used inside R3F Canvas components.

A new story has been added to Dev/BugRepro that demonstrates:

• Real R3F Canvas component with 3D scene (box mesh with lighting)
• Controls added from within Canvas components
• StrictMode enabled to reproduce the original issue
• Validates the fix works with actual @react-three/fiber usage
• Follows the naming convention: "552 / StrictMode with R3F Canvas should render controls"

Fixes #552

Original prompt

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This section details on the original issue you should resolve

<issue_title>Controls of components inside R3F Canvas not rendering in StrictMode</issue_title> <issue_description>Description When in StrictMode, controls added from components inside a @react-three/fiber Canvas do not display as expected. This behavior disappears when StrictMode is removed.

Reproduce StackBlitz Example

Expected behavior Controls should display correctly even when StrictMode is enabled.

Environment

• react: 19.1.1
• @react-three/fiber: 9.3.0
• leva: 0.10.0
• Browser: Chrome 139.0.7258.67
• OS: macOS 15.6</issue_description>

<agent_instructions>Seems like something with the css calculation in the ui. If you collapse/expand the ui corrects it. The parent to the inputs shows a height value, changing at all resolves. </agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes pmndrs/leva#552

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Project	Deployment	Preview	Comments	Updated (UTC)
leva	Error			Nov 9, 2025 0:28am

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[gsimone]

@copilot please add a storybook with a repro

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[Copilot]

@copilot please add a storybook with a repro

Added StrictMode story in commit d55010c. The story demonstrates the fix with async component mounting (simulating R3F Canvas behavior), nested folders, and interactive mode toggling. You can find it at Advanced/StrictMode in Storybook.

[gsimone]

@copilot do use react-three-fiber to create a realistic reproduction in one of the stories. Add this to the repros story group citing the original issue like the other stories in the category

[Copilot]

@copilot do use react-three-fiber to create a realistic reproduction in one of the stories. Add this to the repros story group citing the original issue like the other stories in the category

Added R3F Canvas reproduction in commit 860b265. The story is now in the Dev/BugRepro group as "552 / StrictMode with R3F Canvas should render controls". It uses actual @react-three/fiber Canvas with a 3D scene and demonstrates controls rendering correctly in StrictMode, citing issue #552 like the other repro stories.