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Re: [filters] Shading language recommendation

From: Dirk Schulze <dschulze@adobe.com>
Date: Tue, 21 Aug 2012 14:32:56 -0700
To: Dean Jackson <dino@apple.com>
CC: Sylvain Galineau <sylvaing@microsoft.com>, "public-fx@w3.org" <public-fx@w3.org>
Message-ID: <C17499E3-2808-4905-B1A5-9A6191E910DF@adobe.com>
Hi,

On Aug 21, 2012, at 2:03 PM, Dean Jackson <dino@apple.com> wrote:

> 
> On 22/08/2012, at 2:52 AM, Sylvain Galineau <sylvaing@microsoft.com> wrote:
> 
>> The normative prose of section 38.2 'Recommended shading language' recommends 
>> GL SL ES [1]. Per RFC2119 this means implementers MUST support GL SL ES 
>> unless there exist 'valid reasons in particular circumstances' to ignore this 
>> recommendation. 
>> 
>> While Microsoft has no objection to defining how the feature works for UAs 
>> that choose GL SL ES as defined by Web GL 1.0, we object to its normative
>> recommendation.
> 
> Can you explain why you object? You mention below what you'd prefer, but don't
> provide reasoning.
> 
> The informative section related to media codecs is there because there are
> well-known IP issues around that technology. As far as I am aware, this does
> not apply in the case of shading languages.
> 
> Also, don't you (Microsoft) agree there is a significant penalty if we don't require
> a single shading language? What is it in particular about GLSL that you object
> to?
CSS Shaders as well as Filter Effects never required GLSL (on base of WebGL), but it is the recommended shading language. Therefore I don't share Sylvain's concerns that an implementation must support GLSL.

> 
> Dean
> 
>> This was the reason for the note in the same section, note
>> which looks at best confusing if not contradictory given the normative 
>> recommendation that precedes it.
>> 
>> We would prefer to follow a pattern similar to the informative section 6.1 in 
>> Media Source Extension[2]: "This section defines segment formats for 
>> implementations that choose to support WebM". We think the ability to specify 
>> multiple shading languages is important, as broadly suggested by the current 
>> note. This allows sites to work with different user agents supporting different 
>> shading languages. For example, a future version of GL SL ES with fallback to 
>> the current version for user agents that don't yet support the new version.
I think it is a good idea to think about future versions of GLSL as well. Therefore adding a feature string that helps the UA to decide if a shader is supported or not, and provide a fullback shader doesn't sound like a bad idea. 

Greetings,
Dirk

>> 
>> 
>> [1] https://dvcs.w3.org/hg/FXTF/raw-file/tip/filters/index.html#recommendation
>> [2] http://dvcs.w3.org/hg/html-media/raw-file/tip/media-source/media-source.html
>> 
>> 
>> 
> 
> 
Received on Tuesday, 21 August 2012 21:33:23 GMT

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