[Vm-dev] JPEGReadWriter2, BitBlt and reusing previously allocated bitmaps

[Laura Perez Cerrato]

Thanks to you all :) Should I commit those?

-Laura Perez Cerrato

On 15 June 2016 at 15:56, David T. Lewis <lewis at mail.msen.com> wrote:

> Done.
>
> Thanks Laura!
>
> Dave
>
>
> >  Hi David, Hi All,
> >
> >    I'd like Laura to be added as a committer to
> source.squeak.org/VMMaker.
> >
> > On Wed, Jun 15, 2016 at 7:28 AM, Laura Perez Cerrato <
> > lauraperezcerrato at gmail.com> wrote:
> >
> >>
> >> Hello everyone,
> >>
> >> Working on JPEGReadWriter2 I noticed that both reading and writing
> >> primitives include a sanity check that ensures that the
> >> source/destination
> >> Smalltalk bitmap has the exact size in bytes needed, instead of checking
> >> that its size is at least that needed. Some BitBlt primitives perform
> >> the
> >> same check, thus not allowing operations with forms with associated
> >> bitmaps
> >> with a size greater than needed.
> >>
> >> When performing operations with images, and specially when such images
> >> are
> >> large in size, actually processing the images takes a small fraction of
> >> the
> >> time it takes to perform the whole operation, while allocating and
> >> deallocating correctly sized bitmaps takes much longer. If one would
> >> wish
> >> to process a series of similarly sized images (with a definite maximum
> >> size), it would be desirable to allocate a bitmap big enough to hold any
> >> of
> >> them only once and then reuse it, thus avoiding the aforementioned cost.
> >> Checking that source and destination bitmaps are big enough instead of
> >> checking that their size is exactly that which is expected would allow
> >> that
> >> optimization.
> >>
> >> A brief exploration of BitBlt and JPEGReadWriter2's code, accompanied
> >> with
> >> some experimenting of what would happen if such sanity checks were
> >> modified
> >> as proposed, has lead me to thinking that these changes would be
> >> benefitial. I haven't observed any undesirable side effects (meaning,
> >> nothing seems to have blown up :)). However, I'm inexperienced in
> >> working
> >> with the VM, so it's rather expectable that I miss something :) Your
> >> input
> >> on the topic would be extremely appreciated.
> >>
> >> The attached changesets contain the proposed set of changes.
> >>
> >> Cheers!
> >>
> >> -Laura Perez Cerrato
> >>
> >>
> >
> >
> > --
> > _,,,^..^,,,_
> > best, Eliot
> >
>
>
>
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