File size: 3,672 Bytes
1e92f2d |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 |
import { nextFontError } from '../next-font-error'
const NORMAL_WEIGHT = 400
const BOLD_WEIGHT = 700
/**
* Convert the weight string to a number so it can be used for comparison.
* Weights can be defined as a number, 'normal' or 'bold'. https://developer.mozilla.org/docs/Web/CSS/@font-face/font-weight
*/
function getWeightNumber(weight: string) {
return weight === 'normal'
? NORMAL_WEIGHT
: weight === 'bold'
? BOLD_WEIGHT
: Number(weight)
}
/**
* Get the distance from normal (400) weight for the provided weight.
* If it's not a variable font we can just return the distance.
* If it's a variable font we need to compare its weight range to 400.
*/
function getDistanceFromNormalWeight(weight?: string) {
if (!weight) return 0
// If it's a variable font the weight is defined with two numbers "100 900", rather than just one "400"
const [firstWeight, secondWeight] = weight
.trim()
.split(/ +/)
.map(getWeightNumber)
if (Number.isNaN(firstWeight) || Number.isNaN(secondWeight)) {
nextFontError(
`Invalid weight value in src array: \`${weight}\`.\nExpected \`normal\`, \`bold\` or a number.`
)
}
// If the weight doesn't have have a second value, it's not a variable font
// If that's the case, just return the distance from normal weight
if (!secondWeight) {
return firstWeight - NORMAL_WEIGHT
}
// Normal weight is within variable font range
if (firstWeight <= NORMAL_WEIGHT && secondWeight >= NORMAL_WEIGHT) {
return 0
}
// Normal weight is outside variable font range
// Return the distance of normal weight to the variable font range
const firstWeightDistance = firstWeight - NORMAL_WEIGHT
const secondWeightDistance = secondWeight - NORMAL_WEIGHT
if (Math.abs(firstWeightDistance) < Math.abs(secondWeightDistance)) {
return firstWeightDistance
}
return secondWeightDistance
}
/**
* If multiple font files are provided for a font family, we need to pick one to use for the automatic fallback generation.
* This function returns the font file that is most likely to be used for the bulk of the text on a page.
*
* There are some assumptions here about the text on a page when picking the font file:
* - Most of the text will have normal weight, use the one closest to 400
* - Most of the text will have normal style, prefer normal over italic
* - If two font files have the same distance from normal weight, the thinner one will most likely be the bulk of the text
*/
export function pickFontFileForFallbackGeneration<
T extends { style?: string; weight?: string },
>(fontFiles: T[]): T {
return fontFiles.reduce((usedFontFile, currentFontFile) => {
if (!usedFontFile) return currentFontFile
const usedFontDistance = getDistanceFromNormalWeight(usedFontFile.weight)
const currentFontDistance = getDistanceFromNormalWeight(
currentFontFile.weight
)
// Prefer normal style if they have the same weight
if (
usedFontDistance === currentFontDistance &&
(typeof currentFontFile.style === 'undefined' ||
currentFontFile.style === 'normal')
) {
return currentFontFile
}
const absUsedDistance = Math.abs(usedFontDistance)
const absCurrentDistance = Math.abs(currentFontDistance)
// Use closest absolute distance to normal weight
if (absCurrentDistance < absUsedDistance) return currentFontFile
// Prefer the thinner font if both have the same absolute distance from normal weight
if (
absUsedDistance === absCurrentDistance &&
currentFontDistance < usedFontDistance
) {
return currentFontFile
}
return usedFontFile
})
}
|