Solution to upload 2x image to WordPress with ACF field and have WordPress generate 1x image

wordpress-1x-acf

// This code was written by Ryan McCahan with input from me, Jeff Bridgforth.

// This code goes into functions.php in your theme. The ACF must have 2x in the label. This code looks for that in the ACF label and generates the 1x image

add_filter('intermediate_image_sizes_advanced', function($new_sizes, $image_meta, $attachment_id){
	if (isset($_POST['_acfuploader']) && stristr(get_field_object($_POST['_acfuploader'])['label'], '2x') !== false) {
		return [
			'image-1x' => [
				'width' => ceil($image_meta['width'] / 2),
				'height' => 0,
				'crop' => false,
			]
		];
	}

  return $new_sizes;
}, 10, 3);

// Code to grab the 1x image

function get1xImage($image) {
  $attachment = wp_get_attachment_metadata($image['ID']);
  if (isset($attachment['sizes']) && isset($attachment['sizes']['image-1x'])) {
    $filename = basename($attachment['file']);
    $url = str_replace($filename, $attachment['sizes']['image-1x']['file'], $attachment['file']);
    return wp_get_upload_dir()['baseurl'] . '/' . $url;
  } else {
    return wp_get_upload_dir()['baseurl']. '/' . $image['file'];
  }
}

// Function to display images in template

function get2xImage($field, $alt = false) {
  ob_start();
?>
  <img src="<?=get1xImage($field);?>" srcset="<?=$field['url']?> 2x" alt="<?=$alt === false ? $field['alt'] : $alt ?>" width="<?php echo $field['width']/2;?>" height="<?php echo $field['height']/2;?>" />
<?php
  return ob_get_clean();
}

// This code will be called in your template
<?=get2ximage(get_field('name_of_your_ACF_field')); ?>