[Mesa-dev] [PATCH] mesa: Fix GL_LUMINANCE handling for compressed textures in glGetTexImage

[Brian Paul]

On 11/16/2012 05:06 PM, Anuj Phogat wrote:
> On Fri, Nov 16, 2012 at 3:28 PM, Ian Romanick<idr at freedesktop.org>  wrote:
>> On 11/16/2012 01:21 PM, Anuj Phogat wrote:
>>>
>>> We need to rebase colors (ex: set G=B=0) when getting GL_LUMINANCE
>>> textures in following cases:
>>> 1. If the luminance texture is actually stored as rgba
>>> 2. If getting a luminance texture, but returning rgba
>>> 3. If getting an rgba texture, but returning luminance
>>>
>>> A similar fix was pushed by Brian Paul for uncompressed textures
>>> in commit: f5d0ced.
>>>
>>> Fixes intel oglconform pxconv-gettex test:
>>> https://bugs.freedesktop.org/show_bug.cgi?id=47220
>>>
>>> Observed no failures in piglit and ogles2conform due to this fix.
>>> This patch will cause failures in intel oglconform pxstore-gettex
>>> and pxtrans-gettex test cases. The cause of a failures is a bug
>>> in test cases. Expected luminance value is calculted incorrectly:
>>
>>                                               calculated
>>
>>> L = R+G+B.
>>
>>
>> This seems weird.  We fail pxconv-gettex because we convert the luminance
>> texture supplied by the application to RGB by replicating the L value to
>> each of R, G, and B.  In this case, and this case only, we need to read back
>> luminance by just returning R.  If the application actually specified an RGB
>> texture, we need to read back luminance by R+G+B.  Right?
>>
> If a texture is stored in RGB/RGBA internal format and we later read it back
> using glGetTexImage. There is no way to find out the format of initial texture
> data supplied by application later in the driver.

Mmm, you should be able to look at gl_texture_image::InternalFormat to 
see what the user requested.  And then check for luminance with 
_mesa_base_tex_format(texImage->InternalFormat)==GL_LUMINANCE.


> For glGetTexImage we
> return L = Tex(R). This is what we do in mesa for uncompressed textures.
> it's different from glReadPixels which returns L=R+G+B.
>
>> Does this match what pxconv-gettex and pxconv-trans expect?
>>
>> This L vs. RGB crap confuses me every time...
>>
> Yeah this is confusing. pxstore-gettex and pxtrans-gettex expects
> L=R+G+B  when getting an rgba texture, but returning luminance.
> Sometime back I submitted a fix to change the expected values
> in pxconv-gettex to L = tex(R). Similar fix is required for failing two
> test cases.

-Brian