srcset.liquid

{%- comment -%}
  Parameters
  img_url: {string} Shopify image_url of the image including a width parameter eg. &width={width}
  max_width: {number} maximum width used for srcset (optional)
{%- endcomment -%}

{%- liquid
  assign widths = '160,320,480,640,800,960,1120,1280,1440,1600,1920,2240,2560' | split: ','
  assign max_width_num = max_width | plus: 0

  capture srcset_output
    for width in widths
      assign width_num = width | plus: 0
      if max_width_num > 0 and max_width_num < width_num
        break
      endif
      unless forloop.first
        echo ', '
      endunless
      echo img_url | replace: '{width}', width | append: ' ' | append: width | append: 'w'
    endfor
  endcapture
  echo srcset_output
-%}