[Mesa-dev] [Bug 84566] Unify the format conversion code

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=84566

--- Comment #22 from Iago Toral <itoral at igalia.com> ---
(In reply to Jason Ekstrand from comment #20)
> (In reply to Iago Toral from comment #18)
> > (In reply to Jason Ekstrand from comment #17)
> > > (In reply to Iago Toral from comment #16)
> > > > We also need new mesa_format enums and pack/unpack functions for byte
> > > > swapped variants of non-array types.
> > > 
> > > Why?  Is this for the byte_swapped flag on GL upload/downloads?  If that's
> > > the only reason, then I'd rather not bother adding mesa types.  We can
> > > easily do a byte swap with _mesa_swizzle_and_convert.  While it's a little
> > > bit of a performance hit, people shouldn't be using that attribute anyway.
> > 
> > I think that won't help in this case. We can only use
> > _mesa_swizzle_and_convert for array types, but as I say, this involves
> > non-array types like GL_UNSIGNED_INT_10_10_10_2. The master converter will
> > not use _mesa_swizzle_and_convert with these, it goes through things like
> > _mesa_unpack_rgba_row and _mesa_pack_float_rgba_row for example (which rely
> > on auto-generated pack/unpack functions). Do you think we should try expand
> > these to consider byte-swapping?
> 
> My inclination on byte-swapping it to keep it out of the master conversion
> function.  It's really an oddity of the old GL api and not a core format
> conversion thing.  No sanely written app should use byte swapping, so I'm
> not too worried about making it fast.  My inclination there is to keep going
> byteswapping and the other format conversion ops in TexImage, GetTexImag,
> ReadPixels, and DrawPixels.  They can call _mesa_swizzle_and_convert to do
> the byteswap operation befor calling into the actual format conversion
> function.

I'll try it this way then.

> The downside here is that there are a few cases where we can do better. 
> However, that's pretty much limited to GL_UNSIGNED_INT_8_8_8_8[_REV] and I
> don't think it's worth the effort.

I am already handling GL_UNSIGNED_INT_8_8_8_8[_REV] with byte swapping when we
generate the mesa_array_format from the gl format and type.(it is only a matter
of reverting the component mapping in this case), so if we want we can have
TexImage and cia handle byte-swapping for all formats but this one.

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