W3C home > Mailing lists > Public > public-respimg@w3.org > August 2014

Re: Multiple downloads

From: Simon Pieters <simonp@opera.com>
Date: Mon, 25 Aug 2014 13:26:16 +0200
To: public-respimg@w3.org, "Thomas Hertog" <thomas.hertog@gmail.com>
Message-ID: <op.xk5bd2y1idj3kv@simons-mbp>
On Fri, 22 Aug 2014 11:56:30 +0200, Thomas Hertog  
<thomas.hertog@gmail.com> wrote:

> Dear,
> first of all, my apologizes if my English isn't well-written. I am not a
> native speaker but I tried my best.
> as I was reading about the picture element combined with the srcset
> attribute, I was excited.
> Because this time we could have responsive images without the burden of
> doing all calculations myself.
> However,
> the reason I want to use multiple files is performance.
> I don't want my users to download a 5MB picture when the biggest they can
> display would contain only 1MB
> As far as I can understand the specification, this problem is still not
> solved by using the picture element combined with the srcset and sizes
> attributes.
> Because what would happen if a viewport is resized (due to someone simply
> resizing their browser window, or an orientation change on mobile).
> Would this mean a new file has to be downloaded for displaying if the new
> area where the image can be displayed reaches a certain (bigger)  
> threshold?
> Let me illustrate with an example.
> A mobile phone with screen size 480x800px navigates to a website. The
> medium sized image gets downloaded because the phone is held in portrait
> mode.
> Once the user rotates his phone and the orientation changes, the browser
> recalculated and discovered a bigger image could be used.
> Will this bigger image be downloaded as well? Or will the other image be
> stretched out? Or even something else I couldn't think of?

What happens when the environment changes is basically up to the user  
agent. The intent is that when using media queries with <source media>,  
the browser will fetch the bigger image because we want art direction to  
be honored (there is an open bug about making this a requirement in the  
spec). However, for URLs specified in srcset, the browser is free to do  
what it thinks is best for the user, whether that is to keep the current  
image or download a bigger one.

Simon Pieters
Opera Software
Received on Monday, 25 August 2014 11:26:48 UTC

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