A texture-data alignment bug when tracing

[Paul Berry]

On 15 September 2012 09:37, José Fonseca <jose.r.fonseca at gmail.com> wrote:

> On Fri, Sep 14, 2012 at 11:22 PM, Carl Worth <cworth at cworth.org> wrote:
> > Paul Berry <stereotype441 at gmail.com> writes:
> >> I think you're right, Jose.  And unless I'm much mistaken, Mesa has
> never
> >> followed this rule correctly.
> >
> > Cool, an implementation bug!
> >
> >> Carl, would you mind sending me the test program you were using to
> >> investigate this?  I'd like to try it on my nVidia machine.  Assuming
> >> that the nVidia driver follows the spec, I'll file a Mesa bug report.
> >
> > Sure thing. It's attached. The program initializes a 2x2 RGB texture
> > with 12 bytes of data, (so according to José's understanding of the
> > specification). And according to that interpretation it should result in
> > a texture with 4 texels, all green.
> >
> > When I run this with Mesa, I get 2 green pixels, then one blue, then one
> > of uncertain color as Mesa reads past my allocated array, (and
> > triggering an error if you run the program under valgrind).
> >
> > I'll be quite interested to see what you find.
>
> I tried on my NVIDIA, and it also shows green green blue black.
>
> I read the spec more detailed, and it seems that "element" is a single
> channel (not a pixel), where a "group" is a pixel.
>
> I've pushed a change that tries to match the spec precisely. I've
> checked that it does the right thing with Paul's sample.
>
> Jose
>

Ok, thanks for checking into this in more detail, Jose.  If I understand
correctly now, it sounds like there is no Mesa bug after all.
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