[Mesa-dev] [PATCH 5/9] gallium: add R8G8_R8B8 and G8R8_B8R8 format

[Christian König]

On 12.03.2012 13:26, Roland Scheidegger wrote:
> Hmm actually I think these new pipe formats are a mistake.
> Why do you need them and don't just use the existing R8G8_B8G8 and
> G8R8_G8B8?
> Do you really care if Y ends up in G channel instead of R? And if you do
> why don't you just use a sampler swizzle?
> The R8G8_B8G8 and G8R8_G8B8 formats are there because these correspond
> to the subsampled DX10 formats. I just see absolutely no point in
> introducing similar formats which just have different channel mapping -
> we generally don't have arbitrary swizzled formats, with the exception
> of "old" ones which can be used for legacy purposes. But no such case
> can be made for these new formats.
Well, we definitely already have separate formats for different channel 
mappings. otherwise we should handle the difference between RGBA and 
BGRA with sampler swizzle’s also.

> (I just checked the i965 docs which doesn't support sampler swizzling,
> and in fact these new formats wouldn't help you there neither, since all
> 4 subsampled ycbcr format map Y to the green channel. So with hw
> supporting sampler swizzling, these formats don't buy you anything, and
> with hw not supporting it they don't help neither as no hardware out
> there supports them anyway.)
> Or is there another reason why you need these formats I'm missing?
Nope, not really I just added them for consistency with the existing 
format handling, and it actually makes the implementation of YUV -> RGB 
conversion a bit easier.

Christian.