[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Public WebGL] Retrieving number of texture channels



On 22 Feb 2010, at 21:28, Chris Marrin wrote:

> 
> On Feb 22, 2010, at 11:50 AM, Johannes Behr wrote:
> 
>> 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.
> 
> 
> I don't think we should blaze the trail here. It seems reasonable that, for now, the author has to know what types of images are being loaded.

But how? Should we add a new extra field to the ImageTexture-Node for the image type?
This would be ignored by all content pipelines and would leave x3dom incompatible to all other x3d implementation. 

For a lot of cases the author could probable not even define the type
since the x3d code could and should be independent of the later loaded image. 

> Of course, I bet clever programming could reveal the type somehow.

Please. If anyone can think about one let us know.

best regards,
johannes

> 
> -----
> ~Chris
> cmarrin@apple.com
> 
> 
> 
> 
> -----------------------------------------------------------
> You are currently subscribe to public_webgl@khronos.org.
> To unsubscribe, send an email to majordomo@khronos.org with
> the following command in the body of your email:
> 

--------
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/


-----------------------------------------------------------
You are currently subscribe to public_webgl@khronos.org.
To unsubscribe, send an email to majordomo@khronos.org with
the following command in the body of your email: