Re: [Mesa3d-users] [SOLVED] Extreme slowdown after update

[Philipp K. K. <pk...@sp...>]

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Lucas Clemente Vella schrieb:

> 
> I finally came to a solution, this line in .drirc configuration file
> (I would not find it without the great DRIconf application):
> 
>             <option name="force_s3tc_enable" value="true" />
> 
> There is no need for libtxc_dxtn, since i945 (and all the chips I
> know) have hardware accelerated DXTn compression; but it seems that if
> Mesa can't find the lib, it disables the support for compression. In
> my case, Ogre was decompressing it in software. The option forces Mesa
> to support the compression even without software fallback (IMHO, what
> should be default),

No, it shouldn't be the default. Enabling this option breaks OpenGL.

libtxc_dxtn is needed if you want S3TC texture (de)compression in your
Mesa-provided OpenGL. Hardware support for S3TC is not enough.

There will always be cases where Mesa has to fall back to software, at
least partially, when you're using some feature that your hardware or
the driver doesn't support (maybe it's glDrawPixles(), maybe it's some
fog option, maybe it's the depth test, maybe it's the render mode,
whatever). And at that moment things will break apart, since the
software fallback won't support S3TC without libtxc_dxtn.

Oh, and none of the chips I know has hardware support for S3TC
_compression_ (though most have support for hardware _decompression_).
The S3TC extension requires support for _compression_, too.

Philipp
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