Texture function opengl specification

[Jerome G. <j.g...@gm...>]

Hi,

I am wondering if i am fully understanding how texture value
should be computed. I am refering here to section 3.8.13
of opengl specification and specialy to table 3.21.

My understanding is that when you got an RGB texture the
As = 1 but when computing you use Ap which equal to the
primary color component of incoming fragment if you are
texture 0, or to the previous A value if you are texture > 0
ie if you are texture 1 you use A from texture 0, if you are
texture 2 you use A from texture 1 right ?

According to fragment program extension, TEX, TXP, ... should
give you the right A value (Ap depending on which texture unit
you are using). I got the feeling that r300/r400 hardware doesn't
follow this. At least fglrx driver (one packaged in ubuntu edgy)
fail at pixel format test using TEX instruction. I also attach a
small app which should test that. If you launch it res should
be (255, 0, 0, 0) but i will be (255, 0, 0, 255). If anyone could
test that on a windows with r300 hardware.

I may also don't fully understand this part of the specification :)
Btw the Ap value seems a bit hard things to follow i guess that
ATI might have choose to save some silicon and simplify design
than to conform to this specification.

best,
Jerome Glisse