PNG support for Emacs on Windows

PNG support for Emacs on Windows

[Robert Thorpe]

Hello,

I've installed Emacs 26.3 on a MS Windows 10 PC.  It seems to work fine.

I wanted PNG support, so I downloaded the PNG library from ezwinports.
I installed it so that the /bin directory is on the path.  I've done this
before.  I'm fairly sure that last time once I'd done that PNG support
just started working.

PNG support doesn't seem to work though.  It gives the error "Cannot
Display Image: (Invalid Image Specification".

I noticed one thing that might be the problem.  I used the 64-bit build
of Emacs.  But, ezwinports only has the 32-bit build of the PNG
library.  I don't know if Windows can deal with a call from a 64-bit
program to a 32-bit library.  If it can't, where can I get a 64-bit
version of the PNG library?

BR,
Robert Thorpe

Re: PNG support for Emacs on Windows

[Óscar Fuentes]

Robert Thorpe <rt@robertthorpeconsulting.com> writes:

> I noticed one thing that might be the problem.  I used the 64-bit build
> of Emacs.  But, ezwinports only has the 32-bit build of the PNG
> library.  I don't know if Windows can deal with a call from a 64-bit
> program to a 32-bit library.  If it can't, where can I get a 64-bit
> version of the PNG library?

You need a 64 bit PNG library. This binary package:

http://ftp.gnu.org/gnu/emacs/windows/emacs-26/emacs-26.3-x86_64.zip

contains the required libpng files, among many others. I recommend that
you simply unzip that package and use Emacs from it instead of what you
have now.

Re: PNG support for Emacs on Windows

[Eli Zaretskii]

> From: Robert Thorpe <rt@robertthorpeconsulting.com>
> Date: Sat, 02 May 2020 23:17:40 +0100
> 
> PNG support doesn't seem to work though.  It gives the error "Cannot
> Display Image: (Invalid Image Specification".
> 
> I noticed one thing that might be the problem.  I used the 64-bit build
> of Emacs.  But, ezwinports only has the 32-bit build of the PNG
> library.  I don't know if Windows can deal with a call from a 64-bit
> program to a 32-bit library.

It can't.

> If it can't, where can I get a 64-bit version of the PNG library?

The same place you got the Emacs binary, I guess.

Re: PNG support for Emacs on Windows

[Robert Thorpe]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Robert Thorpe <rt@robertthorpeconsulting.com>
>> Date: Sat, 02 May 2020 23:17:40 +0100
>> 
>> PNG support doesn't seem to work though.  It gives the error "Cannot
>> Display Image: (Invalid Image Specification".
>> 
>> I noticed one thing that might be the problem.  I used the 64-bit build
>> of Emacs.  But, ezwinports only has the 32-bit build of the PNG
>> library.  I don't know if Windows can deal with a call from a 64-bit
>> program to a 32-bit library.
>
> It can't.
>
>> If it can't, where can I get a 64-bit version of the PNG library?
>
> The same place you got the Emacs binary, I guess.

You mean the version "emacs-26.3-x86_64.zip" with the dependencies
included?  That might work for me, I'm not sure though.

Are there any big advantages to using the 64-bit version instead of the
32-bit version?

BR,
Robert Thorpe

Re: PNG support for Emacs on Windows

[Eli Zaretskii]

> From: Robert Thorpe <rt@robertthorpeconsulting.com>
> Cc: help-gnu-emacs@gnu.org
> Date: Sun, 03 May 2020 14:44:50 +0100
> 
> >> If it can't, where can I get a 64-bit version of the PNG library?
> >
> > The same place you got the Emacs binary, I guess.
> 
> You mean the version "emacs-26.3-x86_64.zip" with the dependencies
> included?

Yes.

> Are there any big advantages to using the 64-bit version instead of the
> 32-bit version?

Larger max buffer size, I guess.  Perhaps also faster operation.

Re: PNG support for Emacs on Windows

[Robert Thorpe]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Robert Thorpe <rt@robertthorpeconsulting.com>
>> Cc: help-gnu-emacs@gnu.org
>> Date: Sun, 03 May 2020 14:44:50 +0100
>> 
>> >> If it can't, where can I get a 64-bit version of the PNG library?
>> >
>> > The same place you got the Emacs binary, I guess.
>> 
>> You mean the version "emacs-26.3-x86_64.zip" with the dependencies
>> included?
>
> Yes.
>
>> Are there any big advantages to using the 64-bit version instead of the
>> 32-bit version?
>
> Larger max buffer size, I guess.  Perhaps also faster operation.

Thank you.

My new job has provided me with two Windows PCs.  I'll try the new way
on one of them and the old way on the other.

BR,
Robert Thorpe