Hello Aron,
On 04/05/2011 04:16 PM, Aron Bierbaum wrote:
> After spending the afternoon looking through this it appears that IMHO
> OpenSG might [1] be doing something incorrect. Here is what I think is
> going on:
>
> When a geometry core is being processed with a shader material, it
> forces the GeoVertexArrayPumpGroup to use the generic attribute
> functions glVertexAttribPointer instead of the older
> glVertexPointer/glNormalPointer equivalents. Since we are using the
> generic attribute functions, I believe that we need to call
> glBindAttribLocation in order to access these values in the shaders.
>
> So I believe that I can't access the texture coordinates using the old
> gl_MultiTexCoord0 attribute because OpenSG is using
> glVertexAttribPointer instead of glTextureCoordPointer.
yes, unfortunately ATI is not aliasing generic and legacy attributes.
> Also I can't
> access the vertex attributes using a user-defined attribute because
> OpenSG doesn't allow me to specify the attribute indices in the SHL
> chunk using glBindAttribLocation.
yes, there is currently no way to map an attribute name from a shader to
the location and bind a geo property to it, so unless I'm missing
something there is currently no way to make use of generic attributes.
> Does this sound correct? If it is this would essentially mean that
> things are only currently working on NVIDIA hardware because the driver
> still binds the gl_MultiTexCoord0 attribute to "generic" attributes at
> index/slot 8.
yes, I believe your analysis is correct. I think that we should probably
just modify the code to always use the legacy attribute functions. As a
second step we can consider how to assign names to geo properties so
they can be mapped to attribute locations.
Cheers,
Carsten
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