[Pixman] [PATCH 1/2] Remove the 8e extra safety margin in COVER_CLIP analysis

Pekka Paalanen ppaalanen at gmail.com
Mon Sep 14 06:57:02 PDT 2015

On Sat, 12 Sep 2015 02:10:19 +0100
"Ben Avison" <bavison at riscosopen.org> wrote:

> On Fri, 11 Sep 2015 12:30:23 +0100, Pekka Paalanen <ppaalanen at gmail.com> wrote:
> > As samplers are allowed to fetch the pixel at x2 unconditionally, we
> > require
> >     x1 >= 0
> >     x2 < width
> I may be getting picky, but that's circular logic - the samplers are only
> allowed to fetch the pixel at x2 unconditionally because of the way
> BILINEAR_COVER_CLIP is defined in this piece of code, so you can't use it
> as its own justification. As I wrote the commit log originally, the
> premise is that some samplers expect to be able to fetch the pixel at x2
> unconditionally (on at least one axis) and the conclusion is that we need
> to define BILINEAR_COVER_CLIP to allow that (for now).

I don't think it matters which was first, it is circular to me. If you
write a new fetcher, you see that you are allowed to fetch x2. If you
poke with the flag logic like we do, you must account that fetchers
fetch x2. :-)

> How about:
> Because samplers may fetch the pixel at x2 unconditionally, we require...

Sure, I'll change that.

> Other than that, the series looks good - good thinking about the impact
> of projective transforms (though maybe someday that could do with a more
> rigorous examination).
> Also good to see Bill's way of phrasing the ultimate aim - that it'll be
> defined to be safe to fetch all pixels that have a non-zero weight - made
> it into patch 2. I think it's a clear and concise description.

Yup, it was a nice way to put it.

> I had to look up what bikeshedding meant since you've used it a couple of
> times - very apt. I'll have to drop it into conversation sometime :)


Ok, now just an ack from someone else, and I can push these ASAP.

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