[Mesa-dev] [PATCH 2/2] mesa: use the EXT_texture_compression_s3tc enable flag for all S3TC extensions

[Ian Romanick]

On 10/29/2012 02:47 AM, Philipp Klaus Krause wrote:
> Am 28.10.2012 20:51, schrieb Kenneth Graunke:
>
>> This makes sense to me.  The original reason for splitting out the ANGLE
>> vs. EXT bits was that the ANGLE extension only requires decompression,
>> while the other two require both compression and decompression.  So that
>> one could be advertised even without libtxc_dxtn.
>>
>> Of course, now that we've decided to simply lie and fall back to
>> GL_COMPRESSED_RGB[A] when the user asks for online compression and we
>> don't have libtxc_dxtn, this isn't a problem.  So we can simplify.
>
> I can see how one wants to lie about EXT_texture_compression_s3tc and
> give users a broken GL by default, since that's what they want. AFAIK
> previously it was a driconf option, but enabling it was too much of a
> burden on the user.
> Still there might be some users that want standard-compliant behaviour
> without having libtxc_dxtn installed. Why not give them a driconf option
> they can use to disable EXT_texture_compression_s3tc when libtxc_dxtn is
> not there?

I got some push-back from an ISV for this reason about my "Enable S3TC 
always" patch.  They want to know if on-line compression is actually 
available.  I think the right way to do that is to expose all of the 
extensions except EXT_texture_compression_s3tc.

Perhaps there should be two flags:

- One for EXT_texture_compression_s3tc

- One for EXT_texture_compression_dxt1, ANGLE_texture_compression_dxt*, 
and S3_s3tc.

This is similar the current situation, but the partitioning is different.