imagemagick format detection code

imagemagick format detection code

[Lars Magne Ingebrigtsen]

duckduckgo outputs images as gzipped .ico files, and eww can now almost
display them.  But!  If I create the image from the data in the buffer,
I just get a square which imagemagick uses to tell us "nuh-huh; don't
understand": 

(with-temp-buffer
  (set-buffer-multibyte nil)
  (insert-file-contents-literally "/tmp/b.ico")
  (let ((image (create-image (buffer-string) 'imagemagick t)))
    (pop-to-buffer "*image*")
    (insert-image image "*")))

However, if I create the image with

(create-image "/tmp/b.ico" 'imagemagick)

then it works fine.

Does anybody have any, er, insights to offer here?

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Re: imagemagick format detection code

[Lars Magne Ingebrigtsen]

This is apparently a known bug -- ImageMagick isn't able to guess that
something is an ico file, so it needs "help" from the file name.  So one
could say something like

    MagickSetFilename(wand, "ico:favicon.ico");

But then we'd need to keep an alist of MIME types to suffixes like

Content-Type: image/x-icon

and feed that into `create-image' (er...  ":guessed-suffix"?) and then
set it with that function.

Meh.

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Re: imagemagick format detection code

[Stefan Monnier]

> and feed that into `create-image' (er...  ":guessed-suffix"?) and then
> set it with that function.

:guessed-suffix sounds like a hack.  Maybe a :format argument would be
better (and the ImageMagick could turn it into a file suffix).

We currently have a bit of a mess wrt to use of "format" and "type"
since they're both used currently to refer to the same thing, which is
not really the type or format of the image but rather something like the
rendering library used.


        Stefan

Re: imagemagick format detection code

[Lars Magne Ingebrigtsen]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> and feed that into `create-image' (er...  ":guessed-suffix"?) and then
>> set it with that function.
>
> :guessed-suffix sounds like a hack.  Maybe a :format argument would be
> better (and the ImageMagick could turn it into a file suffix).

Or we could explicit and call it :content-type, since that's what it
is.  But that may lead callers to expect that it (always) be heeded
instead of treating it as a hint.  Uhm...  :content-type-hint?

And then, as you say, the ImageMagick code in image.c will do the right
thing.

For instance, have an alist where the initial population is just

'(("image/x-icon" "ico"))

and we'd set the file name to (say) "/tmp/foo.ico" before asking
ImageMagick to parse the data blob.

If this doesn't seem too gruesome, I can implement this, and we'll see
whether there are further elements that should be added after a while...

> We currently have a bit of a mess wrt to use of "format" and "type"
> since they're both used currently to refer to the same thing, which is
> not really the type or format of the image but rather something like the
> rendering library used.

Yes.  This will add to the general confusion in this area.

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Re: imagemagick format detection code

[Thien-Thi Nguyen]

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() Lars Magne Ingebrigtsen <larsi@gnus.org>
() Mon, 12 Aug 2013 17:17:39 +0200

   Yes.  This will add to the general confusion in this area.

Another idea (that may or may not increase confusion) is to
use GNU libextractor:

 http://www.gnu.org/software/libextractor/

for image type (format) detection, and perhaps (w/ a SMOP) as an
additional "magic" for ‘magic-mode-alist’, something like:

 (EXTRACTOR-SPEC . FUNCTION)

where EXTRACTOR-SPEC is a non-string (otherwise it would be taken as
REGEXP) form that configures libextractor to DTRT.

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Re: imagemagick format detection code

[Stefan Monnier]

> Or we could explicit and call it :content-type, since that's what it
> is.  But that may lead callers to expect that it (always) be heeded
> instead of treating it as a hint.  Uhm...  :content-type-hint?

I like content-type in the sense that I'd like to see it used as an
intermediate step between file names and major modes.  But I'm not sure
it's the right thing here.

> '(("image/x-icon" "ico"))

For example, here we end up using a non-official content-type because
there's no official content-type for it.

This said, it's probably no worse than hacking up our own
classification, so... yes, I guess it's a good plan.  But please make
them be symbols rather than strings:

 '((image/x-icon . "ico"))

>> We currently have a bit of a mess wrt to use of "format" and "type"
>> since they're both used currently to refer to the same thing, which is
>> not really the type or format of the image but rather something like the
>> rendering library used.
> Yes.  This will add to the general confusion in this area.

We should at least rework the doc to use "type" everywhere, so we can
use :format for the new notion.


        Stefan

Re: imagemagick format detection code

[Lars Magne Ingebrigtsen]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> This said, it's probably no worse than hacking up our own
> classification, so... yes, I guess it's a good plan.  But please make
> them be symbols rather than strings:
>
>  '((image/x-icon . "ico"))

I've now committed an attempt at this.  That is, it works, and one can
now use duckduckgo.com and get nice images in the search results in eww,
but I'm not sure about the implementation.

Perhaps the rummaging around in the alist should have been done on the
elisp side instead of in C.  I always feel that I'm doing something not
quite...  good...  when I'm writing Lisp in C:

  suffix = Fcar (Fcdr (Fassq (content_type, Fsymbol_value (symbol))));

Anyway.  

>>> We currently have a bit of a mess wrt to use of "format" and "type"
>>> since they're both used currently to refer to the same thing, which is
>>> not really the type or format of the image but rather something like the
>>> rendering library used.
>> Yes.  This will add to the general confusion in this area.
>
> We should at least rework the doc to use "type" everywhere, so we can
> use :format for the new notion.

Yup.

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Re: imagemagick format detection code

[Lars Magne Ingebrigtsen]

Lars Magne Ingebrigtsen <larsi@gnus.org> writes:

> Perhaps the rummaging around in the alist should have been done on the
> elisp side instead of in C.  I always feel that I'm doing something not
> quite...  good...  when I'm writing Lisp in C:
>
>   suffix = Fcar (Fcdr (Fassq (content_type, Fsymbol_value (symbol))));
>
> Anyway.  

Especially that one, since it can error out.  I'll fix.

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Re: imagemagick format detection code

[Stefan Monnier]

>> We should at least rework the doc to use "type" everywhere, so we can
>> use :format for the new notion.
> Yup.

Yet I see you've used :content-type rather than :format.


        Stefan

Re: imagemagick format detection code

[Lars Magne Ingebrigtsen]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>> We should at least rework the doc to use "type" everywhere, so we can
>>> use :format for the new notion.
>> Yup.
>
> Yet I see you've used :content-type rather than :format.

Sorry, I misinterpreted you.  I thought you wanted :content-type for
this hint-ey usage.  I'll change it to :format.

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