Re: [webkit-dev] Content-DPR header

[Yoav Weiss]

On Sun, May 31, 2015 at 4:54 AM, Sam Weinig  wrote:

>
> Hi Yoav,
>
> Sorry, but I’m afraid I’m still not really getting it.  Can you get even
> more concrete?  Perhaps provide some a sample page that would need this
> kind of functionality and go through what Content-DPR values would be used?
>
>
Sure. Let's take this very simple sample site
.
If you wanted to optimize the image there with Client-Hints, you'd need
some way to tell the browser that it has been modified, and that even
though you provided it with a 400x400 pixel image, it should display it
over a 200x200 CSS pixel box.
A "Content-DPR" header value of 2 would enable the browser to know that the
server has reacted to the DPR hint request header, and scale the CSS pixels
it displays the image on accordingly.
___
webkit-dev mailing list
webkit-dev@lists.webkit.org
https://lists.webkit.org/mailman/listinfo/webkit-dev

Re: [webkit-dev] Content-DPR header

[Sam Weinig]

> On May 29, 2015, at 2:11 PM, Yoav Weiss  wrote:
> 
> On Fri, May 29, 2015 at 8:34 PM, Sam Weinig  > wrote:
> Hi Yoav,
> 
> Can you give a concrete example of when this will be used?  I’m having 
> trouble understanding when an author will want to change an images intrinsic 
> size but not have control of the markup.
> 
> It's not about control over markup, it's about control over style.
> 
> Let's say you're now given the following task: write a script that will go 
> over all your server's HTML files and make your images responsive by adding a 
> `srcset` attribute to all  tags. Since some of the images may change 
> their display dimensions at different viewport sizes (i.e the "variable 
> width" use case 
> ),
>  you want to add multiple resources with `w` descriptors to each . Each 
> one of these resources will be pointed towards your shiny new image server, 
> which has access to the original high-quality image as well as the currently 
> displayed one (the "src image").
> 
> But, since you don't know if all the images have their dimensions defined in 
> CSS (and you suspect that a large chunk of them don't have CSS based 
> dimensions), you want to make sure that the intrinsic dimensions of the 
> displayed images remain the same even when you deliver images of varying 
> "physical" dimensions. How can you achieve that?
> 
> Well, the answer is, you want to modify the intrinsic size of the delivered 
> images to be the same as the "src image"'s intrinsic dimensions. With 
> Content-DPR, that's easy. You simply set it to the value that is the 
> delivered image width divided by the "src image" width.
> That way, the browser takes the Content-DPR into account, scales the 
> delivered image and it ends up with the same intrinsic dimensions as the "src 
> image".
> 

Hi Yoav,

Sorry, but I’m afraid I’m still not really getting it.  Can you get even more 
concrete?  Perhaps provide some a sample page that would need this kind of 
functionality and go through what Content-DPR values would be used?

- Sam

> If you don't have markup control, the same exercise applies, but would 
> require the full-fledged Client-Hints in order to actually deliver resized 
> images.
>  
> 
>> On May 29, 2015, at 11:23 AM, Yoav Weiss > > wrote:
>> 
>> As a first step towards the Client-Hints implementation, I submitted a patch 
>>  for Content-DPR support 
>> .
>> A discussion followed on the thread, so I'd like to move it to the list, in 
>> order for it to get higher exposure.
>> 
>> Content-DPR is an HTTP response header that enables style-agnostic image 
>> resizing,
> 
> What exactly does "style-agnostic image resizing” mean? I am not familiar 
> with that term 
> 
> It's not an official term. I meant to say that it enables you to perform 
> image resizing without taking into account the style rules that control the 
> way in which the resized image will be displayed.
> 
> 
>> by enabling the server to adapt the image's intrinsic size so that layout 
>> will not break, even if the image's dimensions are not defined in style.
>> 
>> Opinions welcome! :)
>> ___
>> webkit-dev mailing list
>> webkit-dev@lists.webkit.org 
>> https://lists.webkit.org/mailman/listinfo/webkit-dev 
>> 
> 
> 

___
webkit-dev mailing list
webkit-dev@lists.webkit.org
https://lists.webkit.org/mailman/listinfo/webkit-dev

Re: [webkit-dev] Content-DPR header

[Yoav Weiss]

On Sat, May 30, 2015 at 12:32 AM, Simon Fraser 
wrote:

>
> As others have said, doing this at the transport layer seems wrong.
>

HTTP is an application layer protocol, and is already used to convey all
kinds of data about the payload that it delivers, such as content-type,
charset and language. Content-DPR is not very different.
Content-DPR can be thought of as part as the regular content-negotiation
flow, where the browsers may indicate "this is what I need" (e.g. via
Client-Hints request headers) and the server can indicates "this is what I
gave you".


>
> Why not just invent some new metadata that gets put into the image to
> describe some scaling of the intrinsic size?
>

Well, several reasons:
* The same image resource can be used over multiple scenarios (e.g. a 600px
wide image can be used as a 300px image on a retina screen, as well as a
600px image on a 1x screen). In each scenario, the image would need to have
a different intrinsic size.
* Introducing meta data to do that would require a significant effort on
multiple fronts:
 - We would need that meta data to work the same way across all currently
used Web image formats (GIF, PNG, JPEG, SVG, JPEG-2000, WebP and JPEG-XR).
 - We would need to add support for that to the decoding code of all these
formats.
 - We would need the various utilities that create these images to add
support for editing this meta data. This would require a huge eco-system
wide effort.
___
webkit-dev mailing list
webkit-dev@lists.webkit.org
https://lists.webkit.org/mailman/listinfo/webkit-dev

Re: [webkit-dev] Content-DPR header

[Simon Fraser]

> On May 29, 2015, at 2:11 PM, Yoav Weiss  wrote:
> 
> On Fri, May 29, 2015 at 8:34 PM, Sam Weinig  > wrote:
> Hi Yoav,
> 
> Can you give a concrete example of when this will be used?  I’m having 
> trouble understanding when an author will want to change an images intrinsic 
> size but not have control of the markup.
> 
> It's not about control over markup, it's about control over style.
> 
> Let's say you're now given the following task: write a script that will go 
> over all your server's HTML files and make your images responsive by adding a 
> `srcset` attribute to all  tags. Since some of the images may change 
> their display dimensions at different viewport sizes (i.e the "variable 
> width" use case 
> ),
>  you want to add multiple resources with `w` descriptors to each . Each 
> one of these resources will be pointed towards your shiny new image server, 
> which has access to the original high-quality image as well as the currently 
> displayed one (the "src image").
> 
> But, since you don't know if all the images have their dimensions defined in 
> CSS (and you suspect that a large chunk of them don't have CSS based 
> dimensions), you want to make sure that the intrinsic dimensions of the 
> displayed images remain the same even when you deliver images of varying 
> "physical" dimensions. How can you achieve that?
> 
> Well, the answer is, you want to modify the intrinsic size of the delivered 
> images to be the same as the "src image"'s intrinsic dimensions. With 
> Content-DPR, that's easy. You simply set it to the value that is the 
> delivered image width divided by the "src image" width.
> That way, the browser takes the Content-DPR into account, scales the 
> delivered image and it ends up with the same intrinsic dimensions as the "src 
> image".
> 
> If you don't have markup control, the same exercise applies, but would 
> require the full-fledged Client-Hints in order to actually deliver resized 
> images.

As others have said, doing this at the transport layer seems wrong.

Why not just invent some new metadata that gets put into the image to describe 
some scaling of the intrinsic size?

Simon


___
webkit-dev mailing list
webkit-dev@lists.webkit.org
https://lists.webkit.org/mailman/listinfo/webkit-dev

Re: [webkit-dev] Content-DPR header

[Yoav Weiss]

On Fri, May 29, 2015 at 8:34 PM, Sam Weinig  wrote:

> Hi Yoav,
>
> Can you give a concrete example of when this will be used?  I’m having
> trouble understanding when an author will want to change an images
> intrinsic size but not have control of the markup.
>

It's not about control over markup, it's about control over style.

Let's say you're now given the following task: write a script that will go
over all your server's HTML files and make your images responsive by adding
a `srcset` attribute to all  tags. Since some of the images may change
their display dimensions at different viewport sizes (i.e the "variable
width" use case
),
you want to add multiple resources with `w` descriptors to each . Each
one of these resources will be pointed towards your shiny new image server,
which has access to the original high-quality image as well as the
currently displayed one (the "src image").

But, since you don't know if all the images have their dimensions defined
in CSS (and you suspect that a large chunk of them don't have CSS based
dimensions), you want to make sure that the intrinsic dimensions of the
displayed images remain the same even when you deliver images of varying
"physical" dimensions. How can you achieve that?

Well, the answer is, you want to modify the intrinsic size of the delivered
images to be the same as the "src image"'s intrinsic dimensions. With
Content-DPR, that's easy. You simply set it to the value that is the
delivered image width divided by the "src image" width.
That way, the browser takes the Content-DPR into account, scales the
delivered image and it ends up with the same intrinsic dimensions as the
"src image".

If you don't have markup control, the same exercise applies, but would
require the full-fledged Client-Hints in order to actually deliver resized
images.


>
> On May 29, 2015, at 11:23 AM, Yoav Weiss  wrote:
>
> As a first step towards the Client-Hints implementation, I submitted a
> patch  for Content-DPR
> support
> .
> A discussion followed on the thread, so I'd like to move it to the list,
> in order for it to get higher exposure.
>
> Content-DPR is an HTTP response header that enables style-agnostic image
> resizing,
>
>
> What exactly does "style-agnostic image resizing” mean? I am not familiar
> with that term
>

It's not an official term. I meant to say that it enables you to perform
image resizing without taking into account the style rules that control the
way in which the resized image will be displayed.


> by enabling the server to adapt the image's intrinsic size so that layout
> will not break, even if the image's dimensions are not defined in style.
>
> Opinions welcome! :)
> ___
> webkit-dev mailing list
> webkit-dev@lists.webkit.org
> https://lists.webkit.org/mailman/listinfo/webkit-dev
>
>
>
___
webkit-dev mailing list
webkit-dev@lists.webkit.org
https://lists.webkit.org/mailman/listinfo/webkit-dev

Re: [webkit-dev] Content-DPR header

[Sam Weinig]

Hi Yoav,

Can you give a concrete example of when this will be used?  I’m having trouble 
understanding when an author will want to change an images intrinsic size but 
not have control of the markup.

> On May 29, 2015, at 11:23 AM, Yoav Weiss  wrote:
> 
> As a first step towards the Client-Hints implementation, I submitted a patch 
>  for Content-DPR support 
> .
> A discussion followed on the thread, so I'd like to move it to the list, in 
> order for it to get higher exposure.
> 
> Content-DPR is an HTTP response header that enables style-agnostic image 
> resizing,

What exactly does "style-agnostic image resizing” mean? I am not familiar with 
that term 

> by enabling the server to adapt the image's intrinsic size so that layout 
> will not break, even if the image's dimensions are not defined in style.
> 
> Opinions welcome! :)
> ___
> webkit-dev mailing list
> webkit-dev@lists.webkit.org
> https://lists.webkit.org/mailman/listinfo/webkit-dev

___
webkit-dev mailing list
webkit-dev@lists.webkit.org
https://lists.webkit.org/mailman/listinfo/webkit-dev

[webkit-dev] Content-DPR header

[Yoav Weiss]

As a first step towards the Client-Hints implementation, I submitted a patch
 for Content-DPR support
.
A discussion followed on the thread, so I'd like to move it to the list, in
order for it to get higher exposure.

Content-DPR is an HTTP response header that enables style-agnostic image
resizing, by enabling the server to adapt the image's intrinsic size so
that layout will not break, even if the image's dimensions are not defined
in style.

Opinions welcome! :)
___
webkit-dev mailing list
webkit-dev@lists.webkit.org
https://lists.webkit.org/mailman/listinfo/webkit-dev