[Pixman] [PATCH 10/15] pixman-filter: don't range-check impulse filter

[Bill Spitzak]

On Tue, Dec 22, 2015 at 2:32 AM, Oded Gabbay <oded.gabbay at gmail.com> wrote:

> On Sat, Dec 12, 2015 at 8:06 PM,  <spitzak at gmail.com> wrote:
> > From: Bill Spitzak <spitzak at gmail.com>
> >
> > The other filters don't range-check, so there is no need for this
> > one to either. It is only called with x==0.
>
> Actually, I tried to stop at this function in gdb and didn't manage to
> do it (using the scale demo). I then looked at the code and it seems
> to me that the only way to reach this function is when both
> reconstruction and sample kernels are IMPLUSE. That's because:
>
> 1. If both reconstruction and sample are *not* IMPLUSE, then of course
> we won't reach it.
> 2. If only one of them is IMPLUSE, than the code will immediately
> return the value of the function of the other kernel, which is *not*
> IMPLUSE.
>
> However, when I put both of them to IMPLUSE in the scale demo, the
> picture simply disappears *and* the impluse_kernel is still not
> reached. Actually, in that case, the integral() func is never reached
> as well.
>
> What am I missing ?
>

I believe at this point the calling code calculated a width of zero for the
filter, and this caused all kinds of problems.

I think you are correct that in most or all versions of this code, that
impulse function is never called, and it could be a null pointer instead.

>
>        Oded
>
> > ---
> >  pixman/pixman-filter.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
> > index fbc657d..00126cd 100644
> > --- a/pixman/pixman-filter.c
> > +++ b/pixman/pixman-filter.c
> > @@ -45,7 +45,7 @@ typedef struct
> >  static double
> >  impulse_kernel (double x)
> >  {
> > -    return (x == 0.0)? 1.0 : 0.0;
> > +    return 1;
> >  }
> >
> >  static double
> > --
> > 1.9.1
> >
> > _______________________________________________
> > Pixman mailing list
> > Pixman at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/pixman
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/pixman/attachments/20151222/aca0f27a/attachment.html>