Fallback mode for image magick?

Fallback mode for image magick?

[Klaus-Dieter Bauer]

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Hello!

Org mode uses the compiled-in image-magick support for scaling in-buffer
images. Sadly, this feature doesn't work with the (precompiled) Windows
version of emacs.

Is there some fallback solution available to get image-scaling through
convert.exe instead transparently faking the imagemagick-magick support to
emacs lisp code?

If not, can someone give me a pointer as to what functions and variables
I'd have to overwrite/supply in order to write such a fallback solution (in
emacs lisp)? I fear that by looking up the code I might end up with a
perfectly working `create-image` function, but modes ignoring it because
they check for some other variable or function.

kind regards, Klaus-Dieter Bauer

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Re: Fallback mode for image magick?

[Lars Magne Ingebrigtsen]

Klaus-Dieter Bauer <bauer.klaus.dieter@gmail.com> writes:

> Org mode uses the compiled-in image-magick support for scaling
> in-buffer images. Sadly, this feature doesn't work with the
> (precompiled) Windows version of emacs.

Doesn't ImageMagick support Windows?

-- 
(domestic pets only, the antidote for overdose, milk.)
  bloggy blog http://lars.ingebrigtsen.no/

Re: Fallback mode for image magick?

[Glenn Morris]

Lars Magne Ingebrigtsen wrote:

> Doesn't ImageMagick support Windows?

From NEWS:

  ** Emacs can be compiled with ImageMagick support.
  [...]
  This feature is not available for the Nextstep or MS ports.

(probably because no-one wrote the Emacs integration parts.)

Re: Fallback mode for image magick?

[Klaus-Dieter Bauer]

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It does. I have a native convert.exe. But emacs (on Unix and Cygwin) now
has builtin ImageMagick support (as in emacs can resize images without
calling an external program). The precompiled Windows binaries don't have
it builtin though and according to Glenn Morris answer it is simply not
available for Windows and NextStep.

Hence I am searching for a solution to emulate the builtin support in a way
such that other people's emacs lisp code doesn't have to be aware of it.
From org-mode I can remember, that they query for some `imagemagick-*`
function or variable that is not defined in the Windows binaries.

2013/6/27 Lars Magne Ingebrigtsen <larsi@gnus.org>

> Klaus-Dieter Bauer <bauer.klaus.dieter@gmail.com> writes:
>
> > Org mode uses the compiled-in image-magick support for scaling
> > in-buffer images. Sadly, this feature doesn't work with the
> > (precompiled) Windows version of emacs.
>
> Doesn't ImageMagick support Windows?
>
> --
> (domestic pets only, the antidote for overdose, milk.)
>   bloggy blog http://lars.ingebrigtsen.no/
>

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Re: Fallback mode for image magick?

[Glenn Morris]

Klaus-Dieter Bauer wrote:

> Is there some fallback solution available to get image-scaling through
> convert.exe instead transparently faking the imagemagick-magick support to
> emacs lisp code?

You could look at how image-dired.el or thumbs.el do it.
Both still use external ImageMagick support (bug#10758).

Re: Fallback mode for image magick?

[Eli Zaretskii]

> From: Lars Magne Ingebrigtsen <larsi@gnus.org>
> Date: Thu, 27 Jun 2013 17:35:08 +0200
> Cc: emacs-devel@gnu.org
> 
> Doesn't ImageMagick support Windows?

It does.  But Emacs on Windows doesn't support ImageMagick.

Re: Fallback mode for image magick?

[Klaus-Dieter Bauer]

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2013/6/27 Glenn Morris <rgm@gnu.org>

> Klaus-Dieter Bauer wrote:
>
> > Is there some fallback solution available to get image-scaling through
> > convert.exe instead transparently faking the imagemagick-magick support
> to
> > emacs lisp code?
>
> You could look at how image-dired.el or thumbs.el do it.
> Both still use external ImageMagick support (bug#10758).
>

Can you elaborate on this?

I appreciate the answer, as it will ease implementing the use of
convert.exe.

My intent however is to write a fix, that makes this a default fallback for
code that wants to use builtin support without the need to edit the third
party source code. Finding out what functions and variables I need to
emulate is the hard part here for me.

I can probably do it by comparing the defined variables in emacs on Cygwin
and native Windows, but it would give a high risk of missing something.

kind regards, Klaus

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Re: Fallback mode for image magick?

[Lars Magne Ingebrigtsen]

Klaus-Dieter Bauer <bauer.klaus.dieter@gmail.com> writes:

> My intent however is to write a fix, that makes this a default
> fallback for code that wants to use builtin support without the need
> to edit the third party source code. Finding out what functions and
> variables I need to emulate is the hard part here for me.

If you could implement native ImageMagick support for Emacs under
Microsoft Windows, that would probably be even better.  :-)

-- 
(domestic pets only, the antidote for overdose, milk.)
  bloggy blog http://lars.ingebrigtsen.no/

Re: Fallback mode for image magick?

[Klaus-Dieter Bauer]

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2013/6/28 Lars Magne Ingebrigtsen <larsi@gnus.org>

> Klaus-Dieter Bauer <bauer.klaus.dieter@gmail.com> writes:
>
> > My intent however is to write a fix, that makes this a default
> > fallback for code that wants to use builtin support without the need
> > to edit the third party source code. Finding out what functions and
> > variables I need to emulate is the hard part here for me.
>
> If you could implement native ImageMagick support for Emacs under
> Microsoft Windows, that would probably be even better.  :-)
>
> --
> (domestic pets only, the antidote for overdose, milk.)
>   bloggy blog http://lars.ingebrigtsen.no/
>

So, I got it to compile by adding DEF_IMGLIB_FN and LOAD_IMGLIB_FN entries
like for the other types, following the hint from an older discussion [1]
and correcting it. For reference I have attached the patches to
nt/configure.bat and src/image.c.

Sadly however, I now can't get the MinGW bundle of ImageMagick working.

convert.exe: UnableToOpenModuleFile
> `C:\Users\klaus\.magick\IM_MOD_RL_PNG_.dll': No such file or directory @
> warning/module.c/GetMagickModulePath/812.


While the function `imagemagick-types` is now defined in the session, still
no resizing occurs, probably because ImageMagick silently fails.

Also in this configuration JPEG is not included in `(imagemagick-types)`
for some reason.

Apparently the official ImageMagick version for Windows is tightly bound to
Visual Studio, which doesn't help the case either.

Honestly, the fallback-solution gets more and more attractive ;)


[1] http://lists.gnu.org/archive/html/emacs-devel/2010-09/msg01585.html

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[-- Attachment #2: image.c.patch --]
[-- Type: application/octet-stream, Size: 3505 bytes --]

--- image.c.orig	2013-07-01 10:21:08.404397000 +0200
+++ image.c	2013-07-01 18:52:44.323104200 +0200
@@ -8236,6 +8236,72 @@
   return Fnreverse (typelist);
 }
 
+#if defined HAVE_NTGUI && defined WINDOWSNT
+
+DEF_IMGLIB_FN (void, MagickWandGenesis, (void));
+DEF_IMGLIB_FN (char** , GetMagickList, ( const char *, unsigned long *));
+DEF_IMGLIB_FN (MagickWand*, NewMagickWand, (void));
+DEF_IMGLIB_FN (MagickBooleanType, MagickSetResolution, (MagickWand *, const double, const double));
+DEF_IMGLIB_FN (MagickBooleanType, MagickPingImage, (MagickWand *, const char *));
+DEF_IMGLIB_FN (size_t, MagickGetNumberImages, (MagickWand *));
+DEF_IMGLIB_FN (MagickWand *, DestroyMagicWand, (MagickWand *));
+DEF_IMGLIB_FN (ImageInfo *, CloneImageInfo, (const ImageInfo *));
+DEF_IMGLIB_FN (ExceptionInfo *, AcquireExceptionInfo, (void));
+DEF_IMGLIB_FN (Image *, ReadImage, (const ImageInfo *, ExceptionInfo *));
+DEF_IMGLIB_FN (void, CatchException, (ExceptionInfo *));
+DEF_IMGLIB_FN (MagickWand *, NewMagickWandFromImage, (const Image *));
+DEF_IMGLIB_FN (size_t, MagickGetImageHeight, (MagickWand *));
+DEF_IMGLIB_FN (size_t, MagickGetImageWidth, (MagickWand *));
+DEF_IMGLIB_FN (MagickBooleanType, MagickScaleImage, (MagickWand *,const size_t,const size_t));
+DEF_IMGLIB_FN (MagickBooleanType, MagickPingImageBlob, (MagickWand *,const void *,const size_t));
+DEF_IMGLIB_FN (MagickBooleanType, MagickReadImageBlob, (MagickWand *, const void *, const size_t));
+DEF_IMGLIB_FN (PixelWand*, NewPixelWand, (void));
+DEF_IMGLIB_FN (void, PixelSetColor, (PixelWand *,const size_t));
+DEF_IMGLIB_FN (MagickBooleanType, MagickRotateImage, (MagickWand *,const PixelWand *,const double));
+DEF_IMGLIB_FN (MagickBooleanType, MagickCropImage, (MagickWand *,const size_t,const size_t,const ssize_t, const ssize_t));
+DEF_IMGLIB_FN (PixelIterator*, NewPixelIterator, (MagickWand*));
+DEF_IMGLIB_FN (void, PixelGetMagickColor, (const PixelWand *,MagickPixelPacket *));
+DEF_IMGLIB_FN (PixelIterator*, DestroyPixelIterator,(PixelIterator *iterator));
+
+static bool 
+init_imagemagick_functions (void)
+{
+  HMODULE library;
+
+  /* Try loading ImageMagick library under probable names.  */
+  if (!(library = w32_delayed_load (Qimagemagick)))
+    return 0;
+
+  LOAD_IMGLIB_FN (library, MagickWandGenesis);
+  LOAD_IMGLIB_FN (library, GetMagickList);
+  LOAD_IMGLIB_FN (library, NewMagickWand);
+  LOAD_IMGLIB_FN (library, MagickSetResolution);
+  LOAD_IMGLIB_FN (library, MagickPingImage);
+  LOAD_IMGLIB_FN (library, MagickGetNumberImages);
+  LOAD_IMGLIB_FN (library, DestroyMagicWand);
+  LOAD_IMGLIB_FN (library, CloneImageInfo);
+  LOAD_IMGLIB_FN (library, AcquireExceptionInfo);
+  LOAD_IMGLIB_FN (library, ReadImage);
+  LOAD_IMGLIB_FN (library, CatchException);
+  LOAD_IMGLIB_FN (library, NewMagickWandFromImage);
+  LOAD_IMGLIB_FN (library, MagickGetImageHeight);
+  LOAD_IMGLIB_FN (library, MagickGetImageWidth);
+  LOAD_IMGLIB_FN (library, MagickScaleImage);
+  LOAD_IMGLIB_FN (library, MagickPingImageBlob);
+  LOAD_IMGLIB_FN (library, MagickReadImageBlob);
+  LOAD_IMGLIB_FN (library, NewPixelWand);
+  LOAD_IMGLIB_FN (library, PixelSetColor);
+  LOAD_IMGLIB_FN (library, MagickRotateImage);
+  LOAD_IMGLIB_FN (library, MagickCropImage);
+  LOAD_IMGLIB_FN (library, NewPixelIterator);
+  LOAD_IMGLIB_FN (library, PixelGetMagickColor);
+  LOAD_IMGLIB_FN (library, DestroyPixelIterator);
+
+  return 1;
+}
+
+#endif /* defined HAVE_NTGUI && defined WINDOWSNT  */
+
 #endif	/* defined (HAVE_IMAGEMAGICK) */
 
 

[-- Attachment #3: configure.bat.patch --]
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--- configure.bat.orig	2013-07-01 10:21:08.404397000 +0200
+++ configure.bat	2013-07-01 15:40:15.038522900 +0200
@@ -133,6 +133,7 @@
 if "%1" == "--without-gnutls" goto withoutgnutls
 if "%1" == "--without-libxml2" goto withoutlibxml2
 if "%1" == "--without-xpm" goto withoutxpm
+if "%1" == "--without-imagemagick" goto withoutimagemagick
 if "%1" == "--with-svg" goto withsvg
 if "%1" == "--distfiles" goto distfiles
 if "%1" == "" goto checkutils
@@ -158,6 +159,7 @@
 echo.   --without-xpm           do not use XPM library even if it is installed
 echo.   --without-gnutls        do not use GnuTLS library even if it is installed
 echo.   --without-libxml2       do not use libxml2 library even if it is installed
+echo.   --without-imagemagick   do not use ImageMagick library even if it is installed
 echo.   --with-svg              use the RSVG library (experimental)
 echo.   --distfiles             path to files for make dist, e.g. libXpm.dll
 if "%use_extensions%" == "0" goto end
@@ -353,6 +355,14 @@
 
 rem ----------------------------------------------------------------------
 
+:withoutimagemagick
+set imagemagicksupport=N
+set HAVE_IMAGEMAGICK=
+shift 
+goto again 
+
+rem ----------------------------------------------------------------------
+
 :distfiles
 set HAVE_DISTFILES=1
 shift
@@ -722,6 +732,31 @@
 set HAVE_RSVG=1
 
 :svgDone
+
+if (%imagemagicksupport%) == (N) goto imagemagickDone
+
+echo Checking for ImageMagick...
+echo #define FOR_MSW 1 >junk.c
+echo #define MAGICKCORE_QUANTUM_DEPTH 16 >>junk.c
+echo #define MAGICKCORE_HDRI_ENABLE 0 >>junk.c
+echo #include "wand/MagickWand.h" >>junk.c
+echo main (){} >>junk.c
+rem   -o option is ignored with cl, but allows result to be consistent.
+echo %COMPILER% %usercflags% %mingwflag% -c junk.c -o junk.obj >>config.log
+%COMPILER% %usercflags% %mingwflag% -c junk.c -o junk.obj >junk.out 2>>config.log
+if exist junk.obj goto haveImagemagick
+
+echo ...wand/MagickWand.h not found, building without ImageMagick support.
+echo The failed program was: >>config.log
+type junk.c >>config.log
+set HAVE_IMAGEMAGICK=
+goto :imagemagickDone
+
+:haveImageMagick
+echo ...ImageMagick header available, building with ImageMagick support.
+set HAVE_IMAGEMAGICK=1
+
+:imagemagickDone
 rm -f junk.c junk.obj junk.err junk.out
 
 rem Any distfiles provided for building distribution? If no, we're done.
@@ -809,6 +844,7 @@
 if not "(%HAVE_GIF%)" == "()" echo #define HAVE_GIF 1 >>config.tmp
 if not "(%HAVE_TIFF%)" == "()" echo #define HAVE_TIFF 1 >>config.tmp
 if not "(%HAVE_XPM%)" == "()" echo #define HAVE_XPM 1 >>config.tmp
+if not "(%HAVE_IMAGEMAGICK%)" == "()" echo #define HAVE_IMAGEMAGICK 1 >>config.tmp
 if "(%HAVE_RSVG%)" == "(1)" echo #define HAVE_RSVG 1 >>config.tmp
 
 echo /* End of settings from configure.bat.  */ >>config.tmp
@@ -893,12 +929,19 @@
  echo   Install libtiff development files or use --without-tiff
 
 :checkgif
-if not "(%HAVE_GIF%)" == "()" goto checkdistfiles
-if (%gifsupport%) == (N) goto checkdistfiles
+if not "(%HAVE_GIF%)" == "()" goto checkimagemagick
+if (%gifsupport%) == (N) goto checkimagemagick
  set libsOK=0
  echo GIF support is missing.
  echo   Install giflib or libungif development files or use --without-gif
 
+:checkimagemagick
+if not "(%HAVE_IMAGEMAGICK%)" == "()" goto checkdistfiles
+if (%imagemagicksupport%) == (N) goto checkdistfiles
+ set libsOK=0
+ echo ImageMagick support is missing.
+ echo   Install ImageMagick development files or use --without-imagemagick
+
 :checkdistfiles
 if "(%HAVE_DISTFILES%)" == "()" goto donelibchecks
 if (%distFilesOk%) == (1) goto donelibchecks
@@ -950,12 +993,14 @@
 set tiffsupport=
 set xpmsupport=
 set svgsupport=
+set imagemagicksupport=
 set libsOK=
 set HAVE_GIF=
 set HAVE_JPEG=
 set HAVE_PNG=
 set HAVE_TIFF=
 set HAVE_XPM=
+set HAVE_IMAGEMAGICK=
 set dbginfo=
 endlocal
 set use_extensions=

Re: Fallback mode for image magick?

[Klaus-Dieter Bauer]

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2013/7/2 Klaus-Dieter Bauer <bauer.klaus.dieter@gmail.com>

> 2013/6/28 Lars Magne Ingebrigtsen <larsi@gnus.org>
>
>> Klaus-Dieter Bauer <bauer.klaus.dieter@gmail.com> writes:
>>
>> > My intent however is to write a fix, that makes this a default
>> > fallback for code that wants to use builtin support without the need
>> > to edit the third party source code. Finding out what functions and
>> > variables I need to emulate is the hard part here for me.
>>
>> If you could implement native ImageMagick support for Emacs under
>> Microsoft Windows, that would probably be even better.  :-)
>>
>> --
>> (domestic pets only, the antidote for overdose, milk.)
>>   bloggy blog http://lars.ingebrigtsen.no/
>>
>
> So, I got it to compile by adding DEF_IMGLIB_FN and LOAD_IMGLIB_FN entries
> like for the other types, following the hint from an older discussion [1]
> and correcting it. For reference I have attached the patches to
> nt/configure.bat and src/image.c.
>
> Sadly however, I now can't get the MinGW bundle of ImageMagick working.
>
> convert.exe: UnableToOpenModuleFile
>> `C:\Users\klaus\.magick\IM_MOD_RL_PNG_.dll': No such file or directory @
>> warning/module.c/GetMagickModulePath/812.
>
>
> While the function `imagemagick-types` is now defined in the session,
> still no resizing occurs, probably because ImageMagick silently fails.
>
> Also in this configuration JPEG is not included in `(imagemagick-types)`
> for some reason.
>
> Apparently the official ImageMagick version for Windows is tightly bound
> to Visual Studio, which doesn't help the case either.
>
> Honestly, the fallback-solution gets more and more attractive ;)
>
>
> [1] http://lists.gnu.org/archive/html/emacs-devel/2010-09/msg01585.html
>

I now got emacs to compile with static linking and image-magick support
linking to the standard binary distribution of ImageMagick for Windows.

Basically that version of emacs works fine. `imagemagick-types` is defined,
jpeg/png images can be displayed when the jpeg-62.dll etc are on PATH,
emacs starts without complaint if they are not.

Imagescaling however still doesn't work.

I cross-checked with Cygwin, there scaling works in org-mode (not though
when doing ``(insert-image (create-image .... :width 100))``).

Is there something I am missing?

kind regards, Klaus

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Re: Fallback mode for image magick?

[Lars Ingebrigtsen]

Klaus-Dieter Bauer <bauer.klaus.dieter@gmail.com> writes:

> I now got emacs to compile with static linking and image-magick
> support linking to the standard binary distribution of ImageMagick for
> Windows.
>
> Basically that version of emacs works fine. `imagemagick-types` is
> defined, jpeg/png images can be displayed when the jpeg-62.dll etc are
> on PATH, emacs starts without complaint if they are not.

Sounds promising.

> Imagescaling however still doesn't work.
>
> I cross-checked with Cygwin, there scaling works in org-mode (not
> though when doing ``(insert-image (create-image .... :width 100))``). 
>
> Is there something I am missing?

Could someone with more knowledge of Emacs under Windows please help
here?  Adding ImageMagick support to the Windows version of Emacs would
be quite useful, I think.  

-- 
(domestic pets only, the antidote for overdose, milk.)
  bloggy blog http://lars.ingebrigtsen.no/

Re: Fallback mode for image magick?

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Sat, 06 Jul 2013 17:31:25 +0200
> Cc: emacs-devel@gnu.org
> 
> > Imagescaling however still doesn't work.
> >
> > I cross-checked with Cygwin, there scaling works in org-mode (not
> > though when doing ``(insert-image (create-image .... :width 100))``). 
> >
> > Is there something I am missing?
> 
> Could someone with more knowledge of Emacs under Windows please help
> here?

Help how?  I don't see anything Windows-specific in the description
above, and know nothing about ImageMagick and how Emacs uses it to
guess what could be wrong.  The OP should debug Emacs to see what
happens when image scaling is being requested, and tell the details.
Perhaps then this will become a Windows specific issue.  For now, this
is an ImageMagick issue.

Btw, statically linking against ImageMagick is a no-starter for
Windows.  But this can be fixed later, once the statically linked
executable works.

Btw^2, what about GraphicsMagick?

Re: Fallback mode for image magick?

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

> Help how?  I don't see anything Windows-specific in the description
> above, and know nothing about ImageMagick and how Emacs uses it to
> guess what could be wrong.

There might be a problem in how he's defined the ImageMagick Emacs
interface functions that leads to stuff, er, not working.  If he posts a
new version of the patch, could you have a look at it and see whether it
looks reasonable?

> Btw^2, what about GraphicsMagick?

I don't know anything about GraphicsMagick.  Is that a fork of ImageMagick?

-- 
(domestic pets only, the antidote for overdose, milk.)
  bloggy blog http://lars.ingebrigtsen.no/

Re: Fallback mode for image magick?

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: bauer.klaus.dieter@gmail.com,  emacs-devel@gnu.org
> Date: Sat, 06 Jul 2013 17:59:11 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Help how?  I don't see anything Windows-specific in the description
> > above, and know nothing about ImageMagick and how Emacs uses it to
> > guess what could be wrong.
> 
> There might be a problem in how he's defined the ImageMagick Emacs
> interface functions that leads to stuff, er, not working.  If he posts a
> new version of the patch, could you have a look at it and see whether it
> looks reasonable?

I won't know where to look.  Not unless someone who knows how Emacs
interfaces with ImageMagick for scaling images describes how this
works.

> I don't know anything about GraphicsMagick.  Is that a fork of ImageMagick?

Yes.

Re: Fallback mode for image magick?

[Glenn Morris]

Eli Zaretskii wrote:

> Btw^2, what about GraphicsMagick?

http://debbugs.gnu.org/cgi/bugreport.cgi?bug=14358

Re: Fallback mode for image magick?

[Klaus-Dieter Bauer]

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2013/7/6 Lars Ingebrigtsen <larsi@gnus.org>

> Eli Zaretskii <eliz@gnu.org> writes:
>
> > Help how?  I don't see anything Windows-specific in the description
> > above, and know nothing about ImageMagick and how Emacs uses it to
> > guess what could be wrong.
>
> There might be a problem in how he's defined the ImageMagick Emacs
> interface functions that leads to stuff, er, not working.  If he posts a
> new version of the patch, could you have a look at it and see whether it
> looks reasonable?


The patch did not change anymore. After what I patched the remaining issues
I had (except for "scaling not working") were compilation problems.

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Re: Fallback mode for image magick?

[Klaus-Dieter Bauer]

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2013/7/6 Eli Zaretskii <eliz@gnu.org>

> [...]
>
> Btw, statically linking against ImageMagick is a no-starter for
> Windows.  But this can be fixed later, once the statically linked
> executable works.
>

I guess there might be a misunderstanding in my compiling-vocabulary here;
What I meant is that I compiled with "--ldflags -static". When I compiled
this way, emacs would start without complaint when any of the DLLs
(including jpeg, png etc) were not available, which is the behaviour I saw
in binary releases for Windows.

When I did not use the -static flag and removed the DLLs from PATH, emacs
would crash on startup saying DLLs are missing.

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Re: Fallback mode for image magick?

[Eli Zaretskii]

> From: Klaus-Dieter Bauer <bauer.klaus.dieter@gmail.com>
> Date: Sun, 7 Jul 2013 11:28:12 +0200
> Cc: Lars Ingebrigtsen <larsi@gnus.org>, emacs-devel@gnu.org
> 
> > Btw, statically linking against ImageMagick is a no-starter for
> > Windows.  But this can be fixed later, once the statically linked
> > executable works.
> >
> 
> I guess there might be a misunderstanding in my compiling-vocabulary here;
> What I meant is that I compiled with "--ldflags -static".

I understood that you did something like that, so there's no
misunderstanding.  My point was that linking statically against
ImageMagick is unacceptable as general-purpose build procedure for
Windows, because the Windows build loads optional libraries
dynamically when needed (and does not fail or crash if they are not
available).

Of course, for testing purposes, it is perfectly valid to try the
static link, as a shortcut.

> When I compiled this way, emacs would start without complaint when
> any of the DLLs (including jpeg, png etc) were not available, which
> is the behaviour I saw in binary releases for Windows.

Your Emacs is statically linked against ImageMagick libraries, and all
the libraries that ImageMagick depend on.  That includes jpeg, png,
etc.  So it's a small wonder Emacs doesn't complain.

> When I did not use the -static flag and removed the DLLs from PATH, emacs
> would crash on startup saying DLLs are missing.

Because ImageMagick depends on them.  Without ImageMagick, when these
DLLs are absent, there are no complaints (and no image support).