From 4763cc71c6ea4c278efe0a66599f0ab7e5ca212f Mon Sep 17 00:00:00 2001
From: Max Thirouin <git@moox.io>
Date: Tue, 19 Nov 2019 21:13:59 +0100
Subject: [PATCH] Document reasoning behind hairlineWidth value

Close #1488
---
 packages/docs/src/apis/StyleSheet/StyleSheet.stories.mdx      | 4 ++--
 .../react-native-web/src/exports/StyleSheet/StyleSheet.js     | 3 +++
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/packages/docs/src/apis/StyleSheet/StyleSheet.stories.mdx b/packages/docs/src/apis/StyleSheet/StyleSheet.stories.mdx
index bcd933f3..1f37691e 100644
--- a/packages/docs/src/apis/StyleSheet/StyleSheet.stories.mdx
+++ b/packages/docs/src/apis/StyleSheet/StyleSheet.stories.mdx
@@ -79,5 +79,5 @@ const styles = StyleSheet.create({
 
 ### hairlineWidth
 
-Enables borders of just one physical pixel on retina screens, otherwise it is
-equal to a CSS value of 1px.
+Equal to 1px. This is not implemented using screen density as browsers may
+round sub-pixel values down to `0`, causing the line not to be rendered.
diff --git a/packages/react-native-web/src/exports/StyleSheet/StyleSheet.js b/packages/react-native-web/src/exports/StyleSheet/StyleSheet.js
index 43663259..7e9c293c 100644
--- a/packages/react-native-web/src/exports/StyleSheet/StyleSheet.js
+++ b/packages/react-native-web/src/exports/StyleSheet/StyleSheet.js
@@ -57,6 +57,9 @@ const StyleSheet = {
     return result;
   },
   flatten: flattenStyle,
+
+  // `hairlineWidth` is not implemented using screen density as browsers may
+  // round sub-pixel values down to `0`, causing the line not to be rendered.
   hairlineWidth: 1
 };