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Re: [Public WebGL] Retrieving number of texture channels



Hi,

>> 
>> is there already a possibility to retrieve the number of present texture
>> channels (intensity, luminance-alpha, rgb or rgba texture) in WebGL?
>> 
>> Because according to the X3D lighting model a material's diffuse color
>> modulates the color of the texture in case of a one or two channel texture,
>> which we need to know for implementing this correctly in X3DOM. If instead
>> the texture has three or four channels (the typical case), the color of the
>> texture is used as the diffuse color.
>> You can find an example demonstrating this issue here:
>> http://x3dom.org/x3dom/example/x3dom_imageChannels.xhtml
> 
> Unfortunately OpenGL ES seems to have dropped the
> glGetTexLevelParameter query, which is needed to query the texture's
> internal format, so WebGL doesn't currently contain it.
> 
> We could probably emulate this call in WebGL implementations on top of
> OpenGL ES by tracking the internal format used when the texture was
> uploaded. In the short term, doing so in your library would be your
> best workaround.

But how should we track it in x3dom? AFAIK is there now method
to ask a HTML image for some internal type or number of channels.

best regards
johannes


> 
> However, there must have been a reason this call was dropped from
> OpenGL ES. I suspect the reason is that glGetTexImage was removed, and
> texture rectangle textures aren't supported, so the need to query the
> texture's width, height and internal format is significantly reduced.
> 
> I am not sure we should add this API into WebGL and diverge from
> OpenGL ES. Other opinions?
> 
> -Ken
> 
>> Regards
>> Yvonne
>> 
>> 
>> --
>> Yvonne Jung
>> Fraunhofer-IGD    | Tel.: ++49-6151-155-290
>> Fraunhoferstr. 5  | Fax.: ++49-6151-155-196
>> 64283 Darmstadt   | email: yvonne.jung@igd.fraunhofer.de
>> Germany           | http://www.igd.fhg.de/igd-a4
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>> 

--------
Dr.-Ing. Johannes Behr	tel: +49-6151-155-510
Fraunhoferstr. 5			fax: +49-6151-155-196
D-64283 Darmstadt		skype: johannesbehr
Germany				web: www.igd.fhg.de/www/igd-a4/


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