Re: png in emacs 25 mingw64

[Stephen Leake <stephen_leake@stephe-leake.org>]

TLDR; I usually have Cygwin in the PATH as well; it has shell tools I
can't get in Mingw (yet). It turns out that is the problem; if I run my
build of Emacs from a Mingw64 shell (no Cygwin in PATH), it can show
PNGs.

More details below.

Question; exactly which path is searched for DLLs? I have two:

PATH from the parent process

exec-path after editing in ~/.emacs

The png image is opened well after ~/.emacs is processed, so does it
look on the edited exec-path for the dll?

Or does the dll search take place during startup, in which case it is
the parent PATH (or exec-path before editing in ~/.emacs).

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Stephen Leake <stephen_leake@stephe-leake.org>
>> Cc: ofv@wanadoo.es,  emacs-devel@gnu.org
>> Date: Sat, 16 Apr 2016 07:17:25 -0500
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> >> From: Stephen Leake <stephen_leake@stephe-leake.org>
>> >> Date: Fri, 15 Apr 2016 16:37:33 -0500
>> >> Cc: emacs-devel@gnu.org
>> >>
>> >> One thing I'd like to fix; my build of emacs 25 does not display png
>> >> files. The binary pretest install does. I'd like to figure out the
>> >> difference.
>> >
>> > Are both binaries in the same directory?
>> 
>> My build is in c:/Projects/emacs/emacs-25-build-mingw64/src (I don't
>> install, so I can easily switch versions), with libpng16-16.dll in
>> d:/msys64/mingw54/bin in PATH.
>> 
>> The error message is "Cannot display image: (Invalid image
>> specification)". I traced thru some of the code that tries to open
>> the image; image.c init-image-library returns nil. I haven't tried
>> running under the debugger to go further.
>> 
>> config.h sets HAVE_PNG true.
>> 
>> 
>> The pretest binary is in d:/Apps/emacs-25.0.90/bin, both emacs.exe and
>> libpng16-16.dll; mingw64 is _not_ in PATH.
>> 
>> cygwin "diff" says the two dlls differ.
>
> So this is the root cause, right there: the DLLs differ.  

I don't see why that has to be the problem; the difference could be in
some date.

> Where did
> you get them?  

One from the MSYS2 distribution, the other from the pretest binary,
which may have been built with the MSYS2 distribution, but I'm not sure.


>Are both 64-bit DLLs? Are they both MinGW DLLs?

I don't know how to tell.

>> depends.exe on emacs and libpng (both builds) reports no obvious errors
>> (it seems there is always something missing on windows; I assume those
>> are optional Windows components).
>
> I didn't mean errors.  Libpng should depend on zlib DLL; 

Yes; zlib1.dll

>do you have
> it? 

Yes; in the respective distributions.

>is it good? 

I don't know how to tell. I guess I need to find some other Mingw64
program that uses it?

>is there only one zlib DLL?

In PATH for each build, yes. Although "type -a zlib1.dll" says "not
found", so it's hard to be sure.

>> The libpng comes from the msys2 package manager, so I assume it's all
>> consistent.
>
> Does it come with zlib DLL, or did you install zlib DLL separately?
> If the latter, they could be inconsistent.

Still from the package manager. Yes, the packages could be inconsistent
with each other.

>> Yes, I figured it was some obscure dll issue, which is why I have not
>> tried to track it down yet. Since the problem is not present in the
>> pretest, I figured it's a problem with my setup, not the Emacs sources,
>> so I did not report a bug.
>
> I don't understand why you (and others) use different PATH
> arrangements to run different binaries, and have multiple versions of
> support DLLs.  

If I want to use the Mingw distribution, I use that path.

If I want to use the Emacs pretest binary distribution, I use that path.

I do _not_ mix distributions.

I have no idea how the Emacs pretest was built; simply assuming it is
the same as my current Mingw installation is almost guarranteed to be
false.

That's what PATH is for.

>Isn't it clear that by doing so you create your own DLL
> hell?  

No, I'm avoiding it by not mixing distributions.

>It's much better to have just one copy of each support DLL, in
> a place that is always on PATH.

That would be nice. I can do that on Debian, that has only one package
manager, and a rigorous distribution policy.

I could do that on Windows by only using MSYS2. But then I would not be
able to use the Emacs pretest.


Hmm. I do usually have Cygwin in the PATH as well; it has shell tools I
can't get in Mingw (yet). It turns out that is the problem; if I run my
build of Emacs from a Mingw64 shell (no Cygwin in PATH), it can show
PNGs.

So your point about mixing distributions is valid; I was not being
careful enough. Most of the time it's not a problem (this is the first
problem I can remember).

-- 
-- Stephe