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[WEB] Round FlashList container measurements to device pixel on web #91799

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mountiny merged 2 commits into from
May 27, 2026
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[WEB] Round FlashList container measurements to device pixel on web #91799

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0da4dfa
Implement roundOffPixel on web
VickyStash May 27, 2026
f8bd162
Add details
VickyStash May 27, 2026
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16 changes: 16 additions & 0 deletions patches/@shopify/flash-list/@shopify+flash-list+2.3.0+010+fix-web-subpixel-rounding.patch
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Original file line number Diff line number Diff line change
@@ -0,0 +1,16 @@
diff --git a/node_modules/@shopify/flash-list/dist/recyclerview/utils/measureLayout.web.js b/node_modules/@shopify/flash-list/dist/recyclerview/utils/measureLayout.web.js
index 17d9812..fe112f1 100644
--- a/node_modules/@shopify/flash-list/dist/recyclerview/utils/measureLayout.web.js
+++ b/node_modules/@shopify/flash-list/dist/recyclerview/utils/measureLayout.web.js
@@ -28,7 +28,10 @@ export function areDimensionsEqual(value1, value2) {
return Math.abs(value1 - value2) <= 1;
}
export function roundOffPixel(value) {
- return value;
+ const dpr = typeof window !== "undefined" && window.devicePixelRatio
+ ? window.devicePixelRatio
+ : 1;
+ return Math.round(value * dpr) / dpr;
}
/**
* Measures the size of the RecyclerView's outer container.
9 changes: 9 additions & 0 deletions patches/@shopify/flash-list/details.md
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Expand Up @@ -74,3 +74,12 @@
- Upstream PR/issue: https://github.com/Shopify/flash-list/issues/2291
- E/App issue: https://github.com/Expensify/App/issues/89933
- PR introducing patch: https://github.com/Expensify/App/pull/91248

### [@shopify+flash-list+2.3.0+010+fix-web-subpixel-rounding.patch](@shopify+flash-list+2.3.0+010+fix-web-subpixel-rounding.patch)

- Reason: Fixes a "Maximum update depth exceeded" infinite render loop on web (mostly Windows with fractional display scaling). `roundOffPixel` on web was a no-op, so subpixel drift in the child container's `getBoundingClientRect()` width re-triggered `ViewHolderCollection`'s `[fixedContainerSize]` layout effect on every measurement. The patch implements `roundOffPixel` to snap to the device-pixel grid (`Math.round(value * devicePixelRatio) / devicePixelRatio`), matching native `PixelRatio.roundToNearestPixel`. Two measurements that paint the same physical pixel now collapse to the same JS value, breaking the loop.
- Files changed: `dist/recyclerview/utils/measureLayout.web.js` only.
- Upstream PR/issue: TBD
- E/App issue: https://github.com/Expensify/App/issues/91584
- Sentry: https://expensify.sentry.io/issues/APP-DQ2
- PR introducing patch: https://github.com/Expensify/App/pull/91799
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