to-device-pixel-ratio.js

import isNumber from 'lodash.isnumber'

export function toDevicePixelRatio(size, options = {}) {
  const {
    ratio = 2,
    scale = 1,
    even = true
  } = options
  const evenFactor = even ? 2 : 1
  const floatSize = parseFloat(size)
  const interpolated = evenFactor * Math.round((floatSize * scale / ratio) / evenFactor)
  if (isNumber(size)) {
    return interpolated
  }
  const unit = size.substring(2)
  return `${interpolated}${unit}`
}

// Alias
export const toDpr = toDevicePixelRatio

to-device-pixel-ratio.scss

@function extend-map($source, $target) {
  @return map-merge($source, $target);
}

@function to-dpr($options: ()) {
    $options: extend-map((
        'size': null,
        'even': true,
        'ratio': 2,
        'scale': 1,
    ), $options);
    $size: map-get($options, 'size');
    $even: map-get($options, 'even');
    $scale: map-get($options, 'scale');
    $ratio: map-get($options, 'ratio');
    $even-factor: 1;
    @if ($even) {
        $even-factor: 2;
    }
    @return $even-factor * round($size * $scale / $ratio / $even-factor);
}