Re: [Mesa3d-dev] Texture formats

[Brian P. <br...@va...>]

Gareth Hughes wrote:
> 
> Brian Paul wrote:
> >
> > In the s/w rasterizer I've been replacing the texture Format and Type
> > checks with comparisons against the new MESA_FORMAT_* tokens.
> >
> > And in the texture-object-completeness function, I'm going to check
> > if all mipmaps are of the same format by comparing the TexFormat field
> > instead of the Format/Type fields.
> >
> > So, the Type field really might not be needed anymore.  However, it
> > wouldn't be bad to keep it around a bit longer, I think.
> 
> Sounds good.
> 
> I have a quick question regarding color lookup tables.  If a driver
> doesn't support paletted textures, the only failure case is when the
> data format is a GL_COLOR_INDEX(_*) type and the internalFormat is
> GL_COLOR_INDEX, right?  If the internalFormat is anything else, it goes
> through the color lookup table, which defaults to 0 for all channels,
> right?

Right.  Though it's the format that would be GL_COLOR_INDEX and the
internalFormat would be GL_COLOR_INDEX_*.


> So, if I've got this right, the driver would have to inspect
> internalFormat if the data format was GL_COLOR_INDEX(_*) and choose an
> appropriate final destination format, skip the first conversion pass,
> call the texstore functions to perform the LUT conversion, and then call
> _mesa_convert_texsubimage*() to convert the GLchan-based post-LUT image
> to the final image format.  Does this sound correct?

That sounds right.  I'd have to review the code to say for certain.

I think a few more utility routines may be in order.  Because in all
the drivers' TexImage*() functions we always have to do something
like this (lots of details omitted):

if (anyPixelTransferOps) {
    allocate tempBuffer
    _mesa_transfer_teximage(dest = tempBuffer, source = userData)
    _mesa_convert_texsubimage2d(dest = texImage->Data, src = tempBuffer);
    free tempBuffer
}
else {
   _mesa_convert_texsubimage2d(dest = texImage->Data, src = tempBuffer);

}


In the 3dfx driver it's more complicated because of the image
rescaling that's sometimes needed.

-Brian