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Re: [Public WebGL] Retrieving number of texture channels



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

-----
~Chris
cmarrin@apple.com




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