Re: [boost] [GIL] Can image::recreate reuse the memory?

Subject: Re: [boost] [GIL] Can image::recreate reuse the memory?
From: TONGARI (tongari95_at_[hidden])
Date: 2013-06-01 13:57:35

2013/6/1 Christian Henning <chhenning_at_[hidden]>

> Sorry for the very late reply.
>
>
> > The function create_view is only called when reusing the image's memory.
> I
> > > guess I don't understand what you mean.
> > >
> >
> > For example, look line 313: the memory address 'tmp' is aligned which may
> > differ from '_memory'.
> >
> > So you can't recreate the view with _memory, instead, you should use the
> > aligned address.
> >
> >
> I understand now. I fixed it.
>

OK

>
> > > > 2) In 'recreate': You have to update _align_in_bytes before calling
> > > > create_view
> > > >
> > >
> > > When the user recreates an image with a different _align_in_bytes we
> need
> > > to reallocate the memory. I added this condition to the code. If the
> > > alignment doesn't change then I don't need to update the member.
> > >
> >
> > You don't have to test the equality of _align_in_bytes & _alloc...
> > Even if _align_in_bytes differs, you could still reuse the space.
> > As for _alloc, I'm not sure if you want to guarantee that even if no
> > reallocation is needed, as long as the user provide another allocator,
> the
> > whole memory should be allocate by it.
> >
> >
> If the new align_in_bytes is larger than the old one it could mean we have
> to reallocate. Do you agree?
>

If total_allocated_size_in_bytes not exceeds, than no need to reallocate.

I'm not sure how a allocator would be implemented, but since it's a default
> > param currently, while the user might just want to use the original one
> > (not the implicitly newly constructed one which may != the orignal), it
> > might surprise the user if he does care about the allocator used, so my
> > suggestion here is to separate it to 2 versions with & without allocator,
> > at least, it won't break the API (I personally would like to drop the
> > Alloc param here...)
> >
> >
> I have implemented two versions now.
>

Be sure to make a note to the user since the behavior is changed.
something like:
"if no allocator is provided to 'recreate', it now uses the previous one
instead of creating a new one"

> > Last but not least, 'total_allocated_size_in_bytes' also depends on
> > '_align_in_bytes', so nevertheless, you have to update it first.
> >
> >> Done.
>
>
BTW, 'mpl::bool_<IsPlanar>()' may be more brief than 'typename
boost::conditional< IsPlanar, mpl::true_, mpl::false_ >::type()'

Regards,