[Vm-dev] Support for reading and writing JPEGs to/from -32, -16, -8 and 8 bit deep forms on V3

Eliot Miranda eliot.miranda at gmail.com
Thu May 26 22:09:50 UTC 2016


Hi Laura,

On Thu, May 26, 2016 at 7:00 AM, Laura Perez Cerrato <
lauraperezcerrato at gmail.com> wrote:

>
> Elliot, Dave,
>
> Thanks for your feedback! I didn't realise the differences between the
> coding practices of JPEGReadWriter2Plugin and other plugins since I
> didn't look at the code of the others. I'll try to get the code of
> JPEGReadWriter2Plugin to bear more resemblance to the rest of the
> codebase. I've taken a brief look at RePlugin's code and the way the C
> code should be placed into external files is still a bit confusing to
> me. Any guidance in this aspect would be greatly appreciated.
>

So the scheme is
a) the generated C source for the Smalltalk plugin class is generated in
src/plugins/PluginName/PluginName.c, and it includes a PluginName.h
b) the PluginName.h lives in
platforms/Cross/plugins/PluginName/PluginName.h.  It should define the
functions and types exported by any C sport for the PluginName.c file to
use.
c) if the C support code is cross-platform it should live in
platforms/Cross/plugins/PluginName/sqPluginName.c, which also includes
PluginName.c.  That's the case here, so refactor the bodies of all plugin
methods so that the C code tat is in cCode: '...here...' strings gets moved
to functions in platforms/Cross/plugins/PluginName/sqPluginName.c.  These
functions can be called anything you like but there's a convention to
prepend "sq" or "io".  For example in the FilePlugin names like
sqFileFlush.  "io" tends to be for more GUI and OS related functionality.
d) if the C code is not cross p;at form, or part of it is not cross
platform, that code goes in
platforms/platformName/plugins/PluginName/sqPlatPluginName.c,
e.g. platforms/win32/plugins/UUIDPlugin/sqWin32UUID.c


>
> As I mentioned earlier, I've been working on handling non-even width
> 16-bit Forms and non-0 modulo 4 width 8 bit Forms. Here are two
> changesets with the implementation of that feature.
>

Thanks!!


>
> Cheers!
> -Laura Perez Cerrato
>
>
> On 19 May 2016 at 23:05, David T. Lewis <lewis at mail.msen.com> wrote:
> >
> > Hi Laura,
> >
> > Thanks very much for posting this. I took a quick look at it and will
> > try to follow up later.
> >
> > To clarify one point: Eliot is using the word "horrible" to refer to
> > some coding practices in the existing JPEGReadWriter2Plugin, and it does
> > not mean that your patches are "horrible".
> >
> >
> > Eliot,
> >
> > Indeed, those giant blocks of #cCode are bad, and somebody (tm) should
> > do something about it. It may not be obvious from looking at the change
> > set, but Laura's updates are are patches against that existing code.
> > So your suggestion is good - either rewrite those portions in proper
> > Smalltalk slang, or just move them out to C code in the platforms
> support.
> >
> > I think that this is probably beyond the scope of what Laura is trying to
> > do here, although I would encourage anyone with an interest in improving
> > the plugins to take a look at reworking the #cCode portions of
> > JPEGReadWriter2Plugin.
> >
> > Dave
> >
> >
> >
> >
> > On Thu, May 19, 2016 at 04:29:15PM -0700, Eliot Miranda wrote:
> >>
> >> Hi Laura,
> >>
> >>     this isn't your fault, but looking at the body of the plugin
> methods,
> >> the code is horrible.  It's essentially 100% C.  The code should really
> be
> >> written in C files, not in Smalltalk methods, following the pattern of
> >> separating plugin code into a Smalltalk plugin larger calling platform
> >> functions written in a C layer.  For example, look at the REPlugin which
> >> does regular expressions.  The source to the machinery is in
> >> platforms/Cross/plugins/RePlugin.  The plugin methods, e.g.
> >> REPlugin>>primPCREExecfromto, do marshalling of Smalltalk objects into C
> >> parameters and then invoke function implemented in
> >> platforms/Cross/plugins/RePlugin, e.g. pcre_exec.  This approach means
> that
> >> there's onlyas much cCode:inSmalltalk: as necessary.  This is far nicer
> >> code to read and fix.
> >>
> >> Do you have energy to rewrite the JPEG plain code to follow this
> pattern?
> >> If so, let me encourage you.  It will improve the code hugely.
> >>
> >> On Thu, May 19, 2016 at 7:06 AM, Laura Perez Cerrato <
> >> lauraperezcerrato at gmail.com> wrote:
> >>
> >> >
> >> > Elliot, Dave,
> >> >
> >> > Thanks for your answers! Here go both the changesets requested. The
> >> > JPEGReadWriter2Plugin changeset was generated using a Squeak Spur
> >> > trunk image, whilst the Graphics changeset was generated using the
> >> > latest stable version of Squeak non-Spur (4.6-15102). However, It
> >> > should also work well with a Squeak Spur trunk image, though I haven't
> >> > tested it's functioning there thoroughly. I haven't yet implemented a
> >> > graceful way for the new primitive to fail if the new version of the
> >> > plugin is absent, so keep that in mind.
> >> >
> >> > I'm currently working on handling non-even width 16-bit Forms and
> >> > non-0 modulo 4 width 8 bit Forms, so I'll hopefully send that to you
> >> > too within this week.
> >> >
> >> > -Laura Perez Cerrato
> >> >
> >> >
> >> > On 18 May 2016 at 22:00, David T. Lewis <lewis at mail.msen.com> wrote:
> >> > >
> >> > > On Wed, May 18, 2016 at 03:56:11PM -0700, Eliot Miranda wrote:
> >> > >>
> >> > >> Hi Laura,
> >> > >>
> >> > >> > On May 18, 2016, at 1:04 PM, Laura Perez Cerrato <
> >> > lauraperezcerrato at gmail.com> wrote:
> >> > >> >
> >> > >> >
> >> > >> > Hello, everyone,
> >> > >> >
> >> > >> > During the past few days I've been working on adding support for
> >> > >> > reading and writing reading and writing JPEGs to/from -32, -16,
> -8
> >> > >> > grayscale and 8 grayscale bit deep forms to
> JPEGReadWriter2Plugin for
> >> > >> > the Squeak Cog V3 VM. Just chiming in to tell you that the work
> is
> >> > >> > done and I'd like to share it with you all. :) I believe this
> changes
> >> > >> > should work on Spur VMs too, but haven't tested thoroughly
> enough to
> >> > >> > ensure that.
> >> > >> >
> >> > >> > How do you handle contributions to the codebase? I assume I'd
> have to
> >> > >> > upload the corresponding changeset to the repository but I'm not
> sure
> >> > >> > if there's anything I should do before.
> >> > >> >
> >> > >> > I have also been working on a few changes to the latest non-Spur
> >> > >> > version of Squeak in order to take advantage of the changes to
> the
> >> > >> > plugin but, since I added a primitive to it and these changes
> use it,
> >> > >> > I think it's prudent to ask you too how those contributions are
> >> > >> > handled. Should I refer to the Squeak-dev mailing list?
> >> > >>
> >> > >> This is indeed a problem.  Talking for myself, until VMs have been
> >> > built that include the code and are generally available one can't
> really
> >> > deploy the behaviour to trunk.  But again waiting for the next release
> >> > feels far too slow.
> >> > >>
> >> > >> One approach is to make the behaviour optional, depending on what
> the
> >> > VM provides, eg checking for primitive failure or a plugin version
> number,
> >> > or simply making the code fail gracefully.
> >> > >>
> >> > >> Another approach is to provide the functionality in an extension
> >> > package, and merging that extension into trunk at the next release.
> >> > >>
> >> > >> Other suggestions folks?
> >> > >>
> >> > >
> >> > > We should take a look at the image side code too. Laura, perhaps
> you can
> >> > > post a change set for that also?
> >> > >
> >> > > Very often a new optional primitive can be handled simply by
> providing
> >> > > some suitable fallback code. That provides a smooth transition,
> because
> >> > > the new feature is immediately available and the system continues
> to work
> >> > > for people who do not yet have the new primitive in their VM.
> >> > >
> >> > > Dave
> >> > >
> >> >
> >> >
> >>
> >>
> >> --
> >> _,,,^..^,,,_
> >> best, Eliot
> >
>
>


-- 
_,,,^..^,,,_
best, Eliot
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