[whatwg] Deferring image load
Kang-Hao (Kenny) Lu
kennyluck at csail.mit.edu
Mon Feb 13 03:00:52 PST 2012
(12/02/13 18:33), Bjartur Thorlacius wrote:
> On 2/13/12, Gray Zhang <otakustay at gmail.com> wrote:
>> 1. On a product description page of a shopping site, there are several
>> *main* pictures of the product, along with about twenty or so camera
>> pictures of the product taken from different angles. When the HTML is
>> parsed, browsers by default simultaneously start downloading all images,
>> potentially making some of the *main* ones invisible.
> Hmm. So you request a way to declare which images are important, and
> wich are not?
For this particular use case, yes, I think so. I do think this use case
has very different characteristics from the other two although currently
they are solved by similar technique.
>> 2. On an album page where hundreds of pictures are expected to be shown,
>> it is often required that pictures currently in a user's screen should
>> appear as fast as possible. Loading of a picture outside the screen can
>> deferred to the time that the picture enters or is about to enter the
>> screen, for the purpose of optimization user experience.
> This seems like something interactive user agents should implement.
But it is currently not reliable to the extent that Web authors can rely
on it. The current spec for <img> says
# User agents may obtain images immediately or on demand.
Is there actually an existing user agent that obtain images on demand?
>> 3. a global switch as a http header or an attribute on html to switch
>> UAs image loading from "obtain images immediately" to "obtain on demand"
>> vice versa.
> Would this not depend equally on factors such as whether the user
> agent would download the images over a metered connection?
Could you elaborate a little more on this? What is a metered connection?
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