Re: dri span patches...

[Roland S. <rsc...@hi...>]

Ville Syrj=E4l=E4 wrote:
> On Thu, Mar 03, 2005 at 05:45:15PM +0100, Roland Scheidegger wrote:
>=20
>>Brian Paul wrote:
>>
>>>Roland Scheidegger wrote:
>>>
>>>
>>>>here's a patch which mainly does 3 things: - convert sis, mach64,
>>>>and radeon to spantmp2. The sis and mach64 drivers got a slight
>>>>change, previously you could not read back alpha values (always
>>>>0xff) and I don't think there was a good reason for that?
>>>
>>>
>>>IIRC, the mach64 doesn't support destination alpha planes.  OpenGL=20
>>>requires that reads of absent alpha planes returns 1.0.  I don't know
>>>if the SiS chip is the same.
>>
>>Are you sure? At least the driver handles things like GL_DST_ALPHA blen=
d
>>factors, wouldn't you get awfully bogus results if it wouldn't support=20
>>destination alpha planes in that case?
>=20
>=20
> Like I said before only the RGB components are blended. You can choose =
to=20
> write 0, 1, As, 1-As, Ad or 1-Ad to the destination alpha=20
> (ALPHA_DST_SEL@ALPHA_TST_CNTL register). Currently the driver seems to=20
> write 0. It would probably be a better idea to write 1 instead.
Sorry, but I just can't see that in the driver. And there's no=20
ALPHA_DST_SEL bit, at least not in the mach64 reg file I have...
Regardless if it can actually blend alpha values or not, there would be=20
some half-way useful alpha values probably in the buffer.

Roland