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

[José Fonseca]

On Tue, 2010-04-27 at 08:59 -0700, Roland Scheidegger wrote:
> 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.

I think it is worthwhile to keep the format swizzle orthogonal to the
sampler view swizzles. It is actually more complex trying to describe
swizzles in terms of the packed vector, since they not always have
unambiguous meaning (bitmasks, subsampled formats, compressed textures).

Jose