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Fix hairline borders not visible (#11527)

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This commit is contained in:
Oleksii Bulenok
2026-08-31 16:11:43 +02:00
committed by GitHub
parent a086a2ebe0
commit 89c8e1cb70
4 changed files with 369 additions and 329 deletions
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patches/react-native@0.86.0.patch.md
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@@ -159,3 +159,22 @@ PR: https://github.com/facebook/react-native/pull/57483
Issue: https://github.com/react/react-native/issues/53450#issuecomment-3298157830
Bandaid fix taken from: https://github.com/react/react-native/commit/581d643a9e59fd88f93757f80194e1efd11bd0e5
## RCTViewComponentView.mm Patch - Hairline border strokes dropped at certain subpixel Y offsets on New Arch
Symptom: dividers built as `borderTopWidth: hairlineWidth` vanish on some screens and not
others, deterministically by the view's absolute subpixel Y. A background fill of the same
geometry always renders.
Cause: Fabric draws borders as a stretched 9-slice image. The consumer
(`RCTAddContourEffectToLayer`) hardcodes the stretchable middle as a 1pt band, which matched
the image the producer built until RN 0.81. facebook/react-native#54237 changed the image
size to `ceil(insets) + 1 + ceil(insets)` without updating that formula, so for fractional
(hairline) insets the labels no longer match the image: transparent filler is treated as a
rigid cap, and when squeezed into a one-pixel-tall layer the sampling can land on it instead
of the stroke - no line.
Fix: compute the middle from the cap insets (`size - caps`) instead of assuming 1pt.
Upstream issue: https://github.com/react/react-native/issues/58054 (repro:
https://github.com/abulenok/HairlineBorderRepro, fails identically on 0.86.0 and 0.87.0).