react-native-fast-image/src/objectFit.ts

FastImage, performant React Native image component.

// objectFit, from the prop or the style, shared by the native (index.tsx) and
// web (index.web.tsx) versions.
import { StyleSheet } from 'react-native'
import type { ImageStyle, ObjectFit } from './index'

// Finds a key (tintColor, objectFit) in a style prop, where the last style
// that sets it wins, as with StyleSheet.flatten, but without flattening (which
// allocates a merged object for an array style on every render).
export function fromStyle<K extends 'tintColor' | 'objectFit'>(
    style: unknown,
    key: K,
): ImageStyle[K] {
    if (Array.isArray(style)) {
        for (let i = style.length - 1; i >= 0; i--) {
            const found = fromStyle(style[i], key)
            if (found !== undefined) return found
        }
        return undefined
    }
    if (typeof style === 'number') {
        // A registered style from StyleSheet.create on older React Native.
        const flattened = StyleSheet.flatten(style as any) as
            | ImageStyle
            | undefined
        return flattened ? flattened[key] : undefined
    }
    return style && typeof style === 'object'
        ? (style as ImageStyle)[key]
        : undefined
}

const FITS: Record<ObjectFit, true> = {
    fill: true,
    contain: true,
    cover: true,
    none: true,
    'scale-down': true,
}

// The objectFit prop, then style's, then cover (null, or a value that isn't
// one of objectFit's, counts as not set).
export function resolveObjectFit(
    objectFit: ObjectFit | null | undefined,
    style: unknown,
): ObjectFit {
    const fit = objectFit != null ? objectFit : fromStyle(style, 'objectFit')
    return fit && FITS[fit] === true ? fit : 'cover'
}