[select] Fix support for transform animations when alignItemWithTrigger is active#3532
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atomiks merged 3 commits intoDec 18, 2025
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| const popupTop = positionerRect.top; | ||
| const popupHeight = positionerRect.height; | ||
| const textCenterY = textRect.top + textRect.height / 2; | ||
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| const transformOriginY = | ||
| popupHeight > 0 ? ((textCenterY - popupTop) / popupHeight) * 100 : 50; | ||
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| const clampedY = clamp(transformOriginY, 0, 100); | ||
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| popupElement.style.setProperty('--transform-origin', `50% ${clampedY}%`); |
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Since the addition of try {} finally {} breaks the diff:
This part is new: it maintains a correct transform origin based on the location of the item.
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| // Ensure we remove any transforms that can affect the location of the popup | ||
| // and therefore the calculations. | ||
| const originalTransform = popupElement.style.transform; | ||
| popupElement.style.transform = 'none'; | ||
| popupElement.style.removeProperty('--transform-origin'); |
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The key solution is to remove any transforms when doing the initial calculations (which is the "final" state of the popup location) then restore it back afterwards.
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LukasTy
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Dec 18, 2025
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Looks nice. 👍
Fixes the initially (on first open) misplaced Popup problem. 👌
P.S. Best to review by adding ?w=1 to the URL (hide whitespace).
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Currently transform animations cause a misalignment with the positioning of
alignItemWithTrigger(more noticeable with smaller initial scales or bigger lists). We disable this on our docs, but shadcn/create is using this as a default. Plus Radix seems to handle it correctly.Exaggerated for effect: https://stackblitz.com/edit/y6zpn7cf
https://deploy-preview-3532--base-ui.netlify.app/react/handbook/animation#animating-select-component-with-motion