web/_includes/img-url.html

{%- comment -%}
  Generate image final URL based on `site.img_cdn`, `page.img_path`

  Arguments:
    src - required, basic image path
    img_path - optional, relative path of image
    absolute - optional, boolean, if true, generate absolute URL

  Return:
    image URL
{%- endcomment -%}

{% assign url = include.src %}

{%- if url -%}
  {% unless url contains ':' %}
    {%- comment -%} CND URL {%- endcomment -%}
    {% assign prefix = site.img_cdn | default: '' %}

    {%- comment -%} Add page image path prefix {%- endcomment -%}
    {% assign url = include.img_path | default: '' | append: '/' | append: url %}

    {% assign url = prefix
      | append: '/'
      | append: url
      | replace: '///', '/'
      | replace: '//', '/'
      | replace: ':', ':/'
    %}

    {% if include.absolute %}
      {% assign url = url | absolute_url %}
    {% else %}
      {% assign url = url | relative_url %}
    {% endif %}
  {% endunless %}
{%- endif -%}

{{- url -}}