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[Reproducer] Text drops its last line when its box crosses y = 2048 on a 3x iOS screen (#58970) #58972

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[Reproducer] Text drops its last line when its box crosses y = 2048 on a 3x iOS screen (#58970) #58972

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77 changes: 66 additions & 11 deletions packages/rn-tester/js/examples/Playground/RNTesterPlayground.js
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Original file line number Diff line number Diff line change
Expand Up @@ -8,31 +8,86 @@
* @format
*/

/**
* Reproducer for facebook/react-native#58970: a wrapped <Text> whose box
* crosses y = 2048 in the scroll content draws one line short on a 3x iOS
* screen.
*
* Yoga rounds a node's height as round(bottom) - round(top), subtracting as
* 32-bit floats. With the top below 2048 and the bottom above, the two edges
* are quantized with different steps and the height comes out one float step
* short: 43.9998779296875 instead of 44 for two lines of lineHeight 22. The
* paragraph view hands that box to TextKit as the NSTextContainer size, the
* second line "doesn't fit", and the text is laid out in the container's clip
* mode as a single line.
*
* Expected: every box shows two lines ("top … / second line").
* Actual: the boxes crossing 2048 on a fraction (with nothing above this
* example: "top 2028+1/3" and "top 2028+2/3") show only their
* first line. Their onLayout height logs as 43.9998779296875 and
* onTextLayout reports 1 line. Texts are positioned absolutely,
* 44pt apart, with fractions 0, 1/3 and 2/3, so one of them crosses
* 2048 on a bad fraction whatever sits above this example.
*/

import type {RNTesterModuleExample} from '../../types/RNTesterTypes';
import type {
LayoutEvent,
TextLayoutEvent,
} from 'react-native/Libraries/Types/CoreEventTypes';

import RNTesterText from '../../components/RNTesterText';
import * as React from 'react';
import {StyleSheet, View} from 'react-native';
import {ScrollView, StyleSheet, Text, View} from 'react-native';

const TOPS = [1896, 1940, 1984, 2028];
const FRACTIONS = [0, 1 / 3, 2 / 3];

function Playground() {
function Playground(): React.Node {
return (
<View style={styles.container}>
<RNTesterText>
Edit "RNTesterPlayground.js" to change this file
</RNTesterText>
</View>
<ScrollView contentOffset={{x: 0, y: 1800}}>
<View style={styles.canvas}>
{TOPS.map((top, i) =>
FRACTIONS.map((fraction, j) => (
<Text
key={`${i}-${j}`}
style={[styles.text, {top: top + fraction, left: 16 + j * 124}]}
onLayout={(e: LayoutEvent) => {
const h = e.nativeEvent.layout.height;
if (h !== 44) {
console.log(`box top=${top + fraction}: height ${h}`);
}
}}
onTextLayout={(e: TextLayoutEvent) => {
const n = e.nativeEvent.lines.length;
if (n !== 2) {
console.log(`box top=${top + fraction}: ${n} line(s)`);
}
}}>
{`top ${top}+${j}/3\nsecond line`}
</Text>
)),
)}
</View>
</ScrollView>
);
}

const styles = StyleSheet.create({
container: {
padding: 10,
canvas: {
height: 2300,
},
text: {
position: 'absolute',
width: 110,
fontSize: 15,
lineHeight: 22,
},
});

export default {
title: 'Playground',
name: 'playground',
description: 'Test out new features and ideas.',
description:
'Text drops its last line when its box crosses y = 2048 on a 3x screen',
render: (): React.Node => <Playground />,
} as RNTesterModuleExample;
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