Re: [Mesa3d-dev] Status of s3tc patent in respect to open-source drivers and workarounds

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

Corbin Simpson schrieb:
> On Mon, Mar 29, 2010 at 5:50 PM, Ian Romanick <id...@fr...> wrote:
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>> Philipp Klaus Krause wrote:
>>
>>> Well, there is TexSubImage2D. Assuming we have a compressed texture
>>> stored internally as some S3TC format and then the application replaces
>>> part of it using TexSubImage2D. According to ARB_texture_compression we
>>> may not go to uncompressed ("the allocation and chosen compressed image
>>> format must not be a function of any other state and cannot be changed
>>> once they are established". And while ARB_texture_compression does not
>>> require TexSubImage2D support, EXT_texture_compression_s3tc does.
>> Ah.  Good catch.  My best guess is that there are few, if any, apps that
>> do that.  Such apps would be easy to detect.  We could enable the
>> non-conformant behavior by default, and provide a driconf switch to
>> disable it.  We'd then need to blacklist apps that use unsupported
>> cases.  Since we can detect these cases, we can log a message when the
>> occur.
>>
>> Does that seem like a reasonable compromise?
> 
> We don't have to compromise at all. If the image is already compressed
> internally, then updating it with TexSubImage or CompressedTexSubImage
> must be done along the block boundaries,

Yes.

> and must be done with
> pre-compressed blocks,

Why?

> so we are never decompressing and recompressing
> the texture.

Philipp