Feature request : Add support for lazy loading images

[heitorPB]

Cross post from getzola/zola#2055:

To make our pages load faster and minimize the use of bandwidth/memory when a user does not scroll a whole page ; we can use the following attribute to make the image load only when needed (lazy loading):

<img src="image.jpg" loading="lazy" />

references :

• https://developer.mozilla.org/en-US/docs/Web/Performance/Lazy_loading#images_and_iframes
• https://caniuse.com/loading-lazy-attr

Is this something that pulldown-cmark is interested in? This could be configurable and not-lazy by default to be consistent with current state.

[Martin1887]

This issue seems easy to implement but the HTML renderer is built as a simple use case of handling parsing events and adding options to it is out of scope, meanwhile setting always the lazy-loading option could be worse for other users.

It makes a lot of sense splitting the HTML renderer to another crate, and that crate could read a TOML file with options like this to have a lot of customizations. However, this will not happen in the short term, because there are other more urgent issues.

Nevertheless, creating a new crate initially handling the current options and with those extensions in mind would be not hard and it would be a good starting point to strip out the HTML renderer in favour of external renderers, so if anyone makes it, it would be appreciated.

Related to #519 and #526.

[heitorPB]

This issue seems easy to implement but the HTML renderer is built as a simple use case of handling parsing events and adding options to it is out of scope, meanwhile setting always the lazy-loading option could be worse for other users.

That totally makes sense and I totally agree.

You mentioned that splitting the HTML renderer to another crate is not in the list of most urgent issues. Where can I find the roadmap and be of help?

[Martin1887]

#519 pull request will be merged relatively soon and #526 will also be fixed relatively soon but a bit later.

However, creating the external crate is not in the roadmap and it is entirely a different project. As commented in #408 (comment), a good starting point to create it can be copying the escape.rs and html.rs modules of this project and making a library crate receiving a MD path and a configuration object and a binary crate that reads a TOML file into a configuration object and a MD path to call the lib crate.

So you can help creating this project :). If you have any questions don't hesitate in asking help.

[Martin1887]

#645 has been created to track all requested features that would fit in a new full-featured HTML renderer crate.