[Mesa-dev] r300g + mesa/st support for EXT_texture_swizzle

[Roland Scheidegger]

On 27.04.2010 17:32, Roland Scheidegger wrote:
> On 27.04.2010 13:13, Dave Airlie wrote:
>> Another trying to figure out gallium patch from me,
>>
>> This is in theory EXT_texture_swizzle support, r300g passes the glean
>> test with this now.
>>
>> Some caveats in the patch (i.e. I'm not sure what exactly is correct
>> state tracker behaviour wrt sampler views).
> 
> Dave,
> 
> Basically looks good but I have some concerns. First, I think the
> extension should not be announced unconditionally but rather based on a
> cap bit. There's hw we care about which can't do this (i965, svga) and
> it seems unreasonable to expect them to do workarounds just so this
> extension can be always exposed.
> Also, I think it won't work correctly if the pipe format itself has a
> swizzle (which is different to rgba). There are really two swizzles
> here, one coming from the extension the other inherited from the format,
> and they need to be combined. Either in the driver or the state tracker,
>  I think it's underspecified right now but I think the swizzle parameter
> should express the hardware view, hence the combining should take place
> in the state tracker. (Also, for depth textures it should also take the
> depth texture mode into account, but that might be out of the scope of
> what you're trying to do.)
> 
> Roland

Actually right now the swizzle seems to represent only the "GL swizzle",
not the format one (looking at the u_sampler_view_default_template). Not
sure though if that's really the right design. In this case the driver
would need to combine the format and extension swizzle.

Roland