[X3D-Public] Web3D.org Front Page

[Joe D Williams]

>>>  <object data="your.wrl" ... >
>>> <param name="src" value="your.wrl" >
>>> </object>
>>>
>>
>> The duplication of data="your.wrl"
>> and
>> name="your.wrl"
>> is just due to the fact that BS didn't recognize the src param.
>
> Presumably you mean "that BS didn't recognize the data attribute".

No, @data is standard and everybody accepts that.
The <param> src, or whatever the X3D browsers makers decide, is the 
one missing last time I checked.
In fact, the last time I looked, Flux was the only one that accepted 
the url via a <param>.

>
>> Flux
>> did, so we used both to cover all.
>> I haven't checked now whether BS or Octaga, and Instant will 
>> recognize
>> the src param.
>>
>> Anyway in the big view, it is better for a plugin to use the 
>> <param> and
>> drop using @data, if possible. One reasin is that the host browser 
>> may
>> treat the content differently if requested in data attr rather than 
>> the
>> src param.
>
> Er, no.
>
> If you don't use the "data" attribute, there's nothing to indicate 
> to the Web browser that it should start the plug-in. .)

Uh no, what actually happens, usually, is that if data is empty the 
the plugin will be started on the stregth of finding a registered 
palyer for the mime in @type.

>  Some current and historic implementations might use the "type" 
> attribute for this purpose; but this is unreliable as the "type" 
> attribute is technically only a hint. (That is, the Web browser 
> could opt not to fetch the data at all if the media type given in 
> "type" were unsupported

http://www.ietf.org/internet-drafts/draft-abarth-mime-sniff-01.txt

is in work now, but they are mostly skipping the hard parts.

True, if the media type is not supported the host won't even try.
There are other problems is the server doesn't provide a matching 
content type.

>
> I haven't tested it yet, but recent bugzilla.mozilla.org activity 
> leads me to suspect that Firefox 3.5 might finally be implementing 
> this more-or-less to spec.

Yes, hard to tell what the spec is because they are sort of honoring 
classid.

http://www.whatwg.org/specs/web-apps/current-work/multipage/embedded-content-0.html#the-object-element

>
>> In particular, the browser may try to 'sniff' content type or other
>> aspects of the file, as well as download the complete file before
>> sending it to the plugin when data is used.
>
> Aside from the "classid" attribute, *the server-provided media type 
> is the only specified means to indicate what plug-in should be 
> started*. That means that a correct implementation cannot start the 
> plug-in until *after* the resource specified in "data" has started 
> downloading.

Fortunately that is not true. Prefereably the host will start the 
plugin if it recognizes the mime even if the @data is blank and the is 
not a <param> with a url.
This is desired because then you can wait to see if the plugin is 
running before sending it a url.

The progblem is that (and I have to keep checking this) is tht IE and 
other browsers won't let you send in a new @data value via the DOM. 
You have to rewrite the entire <object> tag to change the URL. This is 
not ture with a player that accepts a url via the <param> (Flux) 
because you can always send in a new url via the src <param>


>> On the other hand, if src
>> param is used, then the url is sent to the plug when it is ready 
>> and
>> then the plugin asks for the content when it is ready.
>
> A correctly written NPAPI plug-in will be ready for an initial 
> stream. Period.  There is absolutely nothing about VRML or X3D that 
> would make implementing this especially problematic.

Right, The host gets the plugin running, then when the plugin is 
ready, the host sends attributes and params. It is nice that the 
browser can start the plugin without a content file. However, unless 
the plugin can accept a url cvai a param, the object tag si a bit 
dificult to program.

>
>> In the <param>
>> case, the host browser is probably less involved in the loading 
>> process.
>
> Well, it's not involved at all in that case--except potentially 
> though its cache.  That is, the browser is going to fetch the 
> resource specified in "data" *no matter what*.  If the plug-in 
> subsequently uses NPAPI facilities to fetch the resource associated 
> with a "src" param, one can hope that this will just be a cache hit.

These are separate operations, not the same. The process the browser 
uses to get content specified with @data is different than the proces 
when the src <param> is used. THis is why it is important that X3D 
browser makers get cnsensue on what param to use. Since Flux used src, 
so should all the rest, I think. Or pick somehting else. This is not 
important until you understand little details about how object works.

>
> Keep in mind, though, that in such a case, the NPAPI call will 
> provide no different media type information than it would have for 
> the initial stream.
>
> As you suggest, it *is* possible for the plug-in to provide its own 
> resource fetching machinery.  But there are a lot of downsides to 
> that--and not many upsides as far as I can tell:

Sure, it can run 'standalone'.

>
>  * The Web browser's fetch of the initial stream becomes entirely
>    wasted.
>  * You end up writing a lot of code for facilities that are provided
>    by the host Web browser.  If you provide a sophisticated cache 
> like
>    modern Web browsers do, we're talking about *quite* a lot of 
> code.
>    So, more initial development time, more cost to maintain, and 
> more
>    potential for bugs.

Right, it is just one way to do it. Some X3D browsers want to be very 
self-sufficient.

>  * You lose the potential to share cached data with other services
>    provided by the Web browser.  For instance, consider an image
>    referenced from an HTML page that subsequently gets used as a
>    texture in an X3D world.

If the URL is the same, then there may be some chance of reusing it.

>
> If the plug-in just uses the NPAPI facilities for resource fetching, 
> it gets to take advantage of pretty thoroughly tested code that 
> includes a sophisticated cache.  I'm just not sure why a plug-in 
> developer would turn that down.

One whose second choice is be be hosted in a web page?

Thanks and Best Regards,
Joe

>
> -- 
> Braden McDaniel                      e-mail: <braden at endoframe.com>
> <http://endoframe.com>               Jabber: <braden at jabber.org>
>
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