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/**
 * Responsive Image Helper Function
 *
 * @param string $image_id the id of the image (from ACF or similar)
 * @param string $image_size the size of the thumbnail image or custom image size
 * @param string $max_width the max width this image will be shown to build the sizes attribute 
 */

function ar_responsive_image($image_id,$image_size,$max_width){

	// check the image ID is not blank
	if($image_id != '') {

		// set the default src image size
		$image_src = wp_get_attachment_image_url( $image_id, $image_size );

		// set the srcset with various image sizes
		$image_srcset = wp_get_attachment_image_srcset( $image_id, $image_size );

		// generate the markup for the responsive image
		echo 'src="'.$image_src.'" srcset="'.$image_srcset.'" sizes="(max-width: '.$max_width.') 100vw, '.$max_width.'"';

	}
}