[Mesa-dev] [PATCH v3] i965: Fix ETC2/EAC GetCompressed* functions on Gen7 GPUs

[Eero Tamminen]

Hi,

On 02.05.2018 20:19, Matt Turner wrote:
> On Wed, May 2, 2018 at 9:13 AM, Eleni Maria Stea <estea at igalia.com> wrote:
>> Gen 7 GPUs store the compressed EAC/ETC2 images in other non-compressed
>> formats that can render. When GetCompressed* functions are called, the
>> pixels are returned in the non-compressed format that is used for the
>> rendering.
>>
>> With this patch we store both the compressed and non-compressed versions
>> of the image, so that both rendering commands and GetCompressed*
>> commands work.
>>
>> Also, the assertions for GL_MAP_WRITE_BIT and GL_MAP_INVALIDATE_RANGE_BIT
>> in intel_miptree_map_etc function have been removed because when the
>> miptree is mapped for reading (for example from a GetCompress*
>> function) the GL_MAP_WRITE_BIT won't be set (and shouldn't be set).
>>
>> Fixes: the following test in CTS for gen7:
>> KHR-GL45.direct_state_access.textures_compressed_subimage test
>>
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104272
> 
> I think you can add
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=81843
> 
> as well :)

This is really lovely feature.

Compressed texture formats are used to:
1. Reduce disk / network usage for the application install
2. Increase run-time performance (by reducing required bandwidth)
3. Reduce program memory usage

At the cost of worse texture quality.

Mesa transparently converting ETC to uncompressed data on platforms that
don't support ETC in HW, means that application doesn't get 2), just
worse texture quality, although some applications would have capability
to fall back to another (HW supported) texture compression format.

And this new patch means that instead of 3), memory usage actually
_increases_ compared to application using non-compressed textures
directly.


Some (many?) applications might fail to run if ETC isn't supported, so
I  understand why this feature is done, but it would be nice to have
some better way to handle it.

Maybe some new extension that can be used by future game engines &
application toolkits to query which of the compressed texture formats
are faked, so that they can instead select a compression format that
actually provides run-time benefits?


	- Eero