[webkit-dev] ProgressEvents for Images

[Hans Muller]

There's a brief discussion of the cross-origin case in the
""ProgressEvents for Images" WhatWG thread:
http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2012-January/034362.htm
l and the WebKit bug about this proposed feature:
https://bugs.webkit.org/show_bug.cgi?id=76102

For cross-site images for which crossOrigin is not set, we'd proposed
"normalizing" the loaded and size ProgressEvent attributes:

ProgressEvents for cross-origin images should not reveal the actual
resource size per 
http://www.w3.org/TR/progress-events/#security-considerations. This could
be avoided by dispatching ProgressEvents with lengthComputable=false (and
loaded=0, total=0) for cross-origin images. Alternatively we could
dispatch a subclass of ProgressEvent with normalized total and loaded
attributes. A normalized image ProgressEvent wouldn't expose the actual
size of the resource being downloaded but it would still enable developers
to observe relative progress. Normalization would set total to a constant
like 1000, and loaded to a relatively correct value.

The motivation for providing progress events in the cross origin case is
applicaitons like image galleries, that just display a list of image URLs.
 Displaying (possibly "normalized") download progress for images that will
be displayed seems desirable.



- Hans


On 1/23/12 3:42 PM, "Charles Pritchard" <chuck at jumis.com> wrote:

>On 1/23/12 2:55 PM, Dean Jackson wrote:
>> On 17/01/2012, at 10:41 AM, Bear Travis wrote:
>>
>>> <img id="image" src="sample.jpg"
>>>      onloadstart="showProgressBar()"
>>>      onprogress="updateProgressBar(event)"
>>>      onloadend="hideProgressBar()"/>
>>>
>>> Developers have taken various tacks to enable progress reporting, for
>>>example
>>> in some cases XHR can be used to download image files.  Max Vujovic
>>>just
>>> published a blog about the practicalities of doing so:
>>> 
>>>http://blogs.adobe.com/openweb/2012/01/13/html5-image-progress-events/.
>>> We
>>> think it would be preferable to provide support for image progress
>>>events
>>> directly.
>> I think this would be extremely useful. It would require a proposal to
>> W3C or WHATWG though.
>
>Seems like this would need to follow CORS.
>Even disclosing the file size is going too far for cross-domain without
>CORS.
>
>-Charles
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