[webkit-dev] Lazy loading

[Simon Fraser]

> On Oct 28, 2019, at 11:39 AM, Rob Buis <rbuis at igalia.com> wrote:
> 
> Hi,
> 
> I made a lazy image loading prototype earlier this year (https://bugs.webkit.org/show_bug.cgi?id=196698) and have been splitting it up into reviewable patches. The main implementation part landed recently so I am wondering about the next steps.
> 
> One thing left to do for sure is cleaning up/adding tests. For one there are tests in http/tests/lazyload which can just be WPT tests, so I'll work in this area for sure. As usual, while adding new tests bugs may show up and more patches will be needed.
> 
> Another possible task is implementing metadata fetch, but it makes the code more complex and chromium has backtracked from it.
> 
> Changing the behavior of loading=auto to make lazy loading the default seems risky and should possibly only be done when lazy image loading is deemed stable enough.

Agreed. Is there any compat data from other browsers?

> 
> Yet another possible task is making lazy loading work for CSS backgrounds, this is implemented in the prototype but I don't think there are many tests for it.
> 
> A related task is implementing lazy loading for iframe's, I took a quick look and this looks like similar work to lazy image loading, but should be much easier to implement now the building blocks are there.

I think this one has the highest potential to give big page loading gains, especially if we can get this one turned on by default (or maybe for cross-origin frames), so I suggest working on this.

Do we have any data from other browsers to know whether enabling lazy-loading iframe by default breaks the web?

> 
> Finally there is the task of setting threshold viewport distance values for triggering deferred loads. I only have access to iOS simulator, so I wonder if that is something Apple could help with?

I would be happy to help.

> 
> I do not have a strong preference among these tasks. Thoughts?
> Cheers,
> 
> Rob.
> 
> P.S: I intend to attend the WebKit Contributors meeting, so feel free to chat with me there about lazy loading.

See you there!

Simon