[Mesa-dev] Bug in _mesa_meta_GenerateMipmap

Brian Paul brianp at vmware.com
Mon Jul 12 11:31:42 PDT 2010

Maciej Cencora wrote:
> Hi,
> while working on failing piglit tests I've stumbled on a problem with 
> _mesa_meta_GenerateMipmap. The function creates new texture images for lower 
> mipmap levels, but during call to glTexImage the format and type are hardcoded 
> to GL_RGBA and GL_UNSIGNED_BYTE respectivily. And that's where the problem 
> arise because base image (the one that other levels are generated from) could 
> have other format and type specified (in failing test texturing/gen-teximage 
> these are GL_RGBA, GL_FLOAT).
> The result is that for base image MESA_FORMAT_ARGB8888 is chosen and for next 
> levels it's MESA_FORMAT_RGBA8888_REV. Of course such texture with images of 
> different formats is invalid and will be missampled by GPU.
> As the fix is not straightforward for me (not sure where to get format and type 
> from, since the gl_texture_image doesn't hold them) could someone more 
> familiar with core mesa take a look at this?

Which driver are you using?

I suspect the problem is the driver's ChooseTextureFormat() callback 
is using more than the 'internalFormat' parameter to choose the actual 
hardware format (i.e. it's also using the format/type params).  Later, 
when we're building the mipmap we don't know the format/type params 
used for creating the base image so we just use GL_RGBA/GL_UNSIGNED_BYTE.

We could save those original params when glTexImage2D() is called to 
create the base image, but that would be of no use if the base image 
was created with glCopyTexImage2D().

We might just be able to "poke" in the actual format for the new image 
to override whatever was chosen.  I'll try to write a patch later...


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