React-native responsive font size [duplicate]

Question

I am developing a tablet app (Android and iOS) with Expo and React-Native.

I managed to make the layout responsive without getting into any problems. After running the app on different size devices, i noticed that i forgot about font size responsiveness.

I tried every npm library that i could find ( react-native-responsive-fontsize, react-native-cross-platform-responsive-dimensions, react-native-responsive-fontsize ). With any one of these, I ran out to the same problem: at app's startup, based on device's orientation, font size renders different. (ie. if I open the app when holding the device in portrait mode, font size is visibly bigger compared to when I open the app when holding the device in landscape mode - landscape mode being my app's default orientation). I tried to lock my app's screen orientation on landscape at startup and that reset it to default after my first component is mounted, but that also didn't help.

I came to the conclusion that this happens because all those libraries are using device's dimensions to make procentual values of what I pass to them, but only referring to only one dimension (width or height), which are different based on initial device orientation.

I tried to implement my own solution, thinking about something that would base on both width and height, not on only one of them, and I had come out with this function:

const height = Dimensions.get('window').height;
const width = Dimensions.get('window').width;

export function proportionalSize(size) {
     let aspectRatioSize = width * height;
     let aspectRatioUnit = aspectRatioSize * 0.00001;

     return parseFloat(size) * 0.1 * aspectRatioUnit;
}

This works only on the device on which I develop the app...font sizes will not keep the same proportions on other devices with different screen size.

I lost enough days modifying font sizes from my entire code, trying to switch between libraries. Do you have any ideas of how can i get over this, or what am I missing? I initially taught that will be my smallest problem, but I was wrong.

Later edit: I noticed that my problem goes away after reloading the app. It happens only at the first render, and after reloading, font-size works just fine.

Answer 1

I think the basing calculations are off...I couldn't get it to scale cleanly between phone and tablet so I changed the calculation to use an aspect ratio based on width / height...this fixed it to display exactly the same on both devices.

import { Dimensions, Platform, PixelRatio } from 'react-native';

const {
  width,
  height,
} = Dimensions.get('window');

export function normalize(size, multiplier = 2) {
  const scale = (width / height) * multiplier;

  const newSize = size * scale;

  return Math.round(PixelRatio.roundToNearestPixel(newSize));
}