How to temporarily show an image in an Emacs buffer?

How to temporarily show an image in an Emacs buffer?

[Marcin Borkowski]

Hi all,

I need to insert an image in the buffer in a way that doesn't interfere
with the undo mechanism.  In other words, `insert-image' won't help me
because (as I understand it) it needs to insert a space or some other
string so that it can put display property on it.  How to achieve this?

To be more precise, imagine I have this buffer:

xxxxxxxxxxxxxxxxxxxxxxxx
yyyyyyyyyyyyyyyyyyyyyyyy

(two lines of text).  I want it to look like this:

xxxxxxxxxxxxxxxxxxxxxxxx
+----------------------+
|                      |
+----------------------+
yyyyyyyyyyyyyyyyyyyyyyyy

in other words, I want a rectangular image (inserted by `insert-image'
or actually `svg-insert-image') to appear between them, but in a way
that doesn't actually change the buffer contents.

Alternatively, it _may_ change the buffer contents but in a way that is
not recorded in `buffer-undo-list'.  Is that possible?

TIA,

-- 
Marcin Borkowski
http://mbork.pl

Re: How to temporarily show an image in an Emacs buffer?

[Marcin Borkowski]

On 2023-03-08, at 05:53, Marcin Borkowski <mbork@mbork.pl> wrote:

> Alternatively, it _may_ change the buffer contents but in a way that is
> not recorded in `buffer-undo-list'.  Is that possible?

I did some experimenting, and this

(defvar no-undo-marker (make-marker))
(defun no-undo-insert ()
  "Test undo."
  (save-excursion
    (let ((buffer-undo-list))
      (set-marker no-undo-marker (point))
      (insert "this can't be undone\n"))))

(defun no-undo-uninsert ()
  (save-excursion
    (goto-char no-undo-marker)
    (let ((buffer-undo-list))
      (when (looking-at-p "this can't be undone\n")
	(delete-char 21)))))

seems to do the trick, but depending on the order of typing and calling
these functions, the undo list becomes corrupted (I get "primitive-undo:
Changes to be undone are outside visible portion of buffer").

Any hints?

-- 
Marcin Borkowski
http://mbork.pl

Re: How to temporarily show an image in an Emacs buffer?

[Ruijie Yu via Users list for the GNU Emacs text editor]

Marcin Borkowski <mbork@mbork.pl> writes:

> On 2023-03-08, at 05:53, Marcin Borkowski <mbork@mbork.pl> wrote:
>
>> Alternatively, it _may_ change the buffer contents but in a way that is
>> not recorded in `buffer-undo-list'.  Is that possible?
>
> I did some experimenting, and this
>
> (defvar no-undo-marker (make-marker))
> (defun no-undo-insert ()
>   "Test undo."
>   (save-excursion
>     (let ((buffer-undo-list))
>       (set-marker no-undo-marker (point))
>       (insert "this can't be undone\n"))))
>
> (defun no-undo-uninsert ()
>   (save-excursion
>     (goto-char no-undo-marker)
>     (let ((buffer-undo-list))
>       (when (looking-at-p "this can't be undone\n")
>   (delete-char 21)))))
>
> seems to do the trick, but depending on the order of typing and calling
> these functions, the undo list becomes corrupted (I get "primitive-undo:
> Changes to be undone are outside visible portion of buffer").
>
> Any hints?

Maybe you can make use of overlays [1]?  That sounds like a great fit
according to the description of your need.

[1]: (info "(elisp) Managing Overlays")

--
Best,


RY

Re: How to temporarily show an image in an Emacs buffer?

[Eli Zaretskii]

> From: Marcin Borkowski <mbork@mbork.pl>
> Date: Wed, 08 Mar 2023 05:53:46 +0100
> 
> I need to insert an image in the buffer in a way that doesn't interfere
> with the undo mechanism.  In other words, `insert-image' won't help me
> because (as I understand it) it needs to insert a space or some other
> string so that it can put display property on it.  How to achieve this?

You can put a display property on the existing text in the buffer
without inserting any new text.  See the node "Other Display
Properties" in the ELisp manual, where it describes the
‘(image . IMAGE-PROPS)’ display property spec.

Re: How to temporarily show an image in an Emacs buffer?

[Marcin Borkowski]

On 2023-03-08, at 14:38, Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Marcin Borkowski <mbork@mbork.pl>
>> Date: Wed, 08 Mar 2023 05:53:46 +0100
>>
>> I need to insert an image in the buffer in a way that doesn't interfere
>> with the undo mechanism.  In other words, `insert-image' won't help me
>> because (as I understand it) it needs to insert a space or some other
>> string so that it can put display property on it.  How to achieve this?
>
> You can put a display property on the existing text in the buffer
> without inserting any new text.  See the node "Other Display
> Properties" in the ELisp manual, where it describes the
> ‘(image . IMAGE-PROPS)’ display property spec.

You're right, of course, but it's a bit more complex than that.  Since
an overlay with the `image' property "hides" the text beneath it, the
key is to create an overlay with a `before-string' property whose value
is a dummy string (say, a space), and put the `image' /text/ property on
that very string.  I did some experiments and it seems to work, though
I'll have a (hopefully) working prototype by the end of the week (no
more time for this today).

Thanks a lot!  (Also, once I have it working, I will definitely describe
it on my blog; I may also copy it here if someone is interested.)

Best,

-- 
Marcin Borkowski
http://mbork.pl

Re: How to temporarily show an image in an Emacs buffer?

[Marcin Borkowski]

On 2023-03-08, at 07:19, Ruijie Yu <ruijie@netyu.xyz> wrote:

> Marcin Borkowski <mbork@mbork.pl> writes:
>
>> On 2023-03-08, at 05:53, Marcin Borkowski <mbork@mbork.pl> wrote:
>>
>>> Alternatively, it _may_ change the buffer contents but in a way that is
>>> not recorded in `buffer-undo-list'.  Is that possible?
>>
>> I did some experimenting, and this
>>
>> (defvar no-undo-marker (make-marker))
>> (defun no-undo-insert ()
>>   "Test undo."
>>   (save-excursion
>>     (let ((buffer-undo-list))
>>       (set-marker no-undo-marker (point))
>>       (insert "this can't be undone\n"))))
>>
>> (defun no-undo-uninsert ()
>>   (save-excursion
>>     (goto-char no-undo-marker)
>>     (let ((buffer-undo-list))
>>       (when (looking-at-p "this can't be undone\n")
>>   (delete-char 21)))))
>>
>> seems to do the trick, but depending on the order of typing and calling
>> these functions, the undo list becomes corrupted (I get "primitive-undo:
>> Changes to be undone are outside visible portion of buffer").
>>
>> Any hints?
>
> Maybe you can make use of overlays [1]?  That sounds like a great fit
> according to the description of your need.
>
> [1]: (info "(elisp) Managing Overlays")

As I said in my reply to Eli, you were right.  (I knew about overlays,
but I didn't know that apparently you can use an overlay with
a `before-string' property /and/ put another display property on the
/string/ being the value of `before-string', which is kind of cool!)

Thanks,

-- 
Marcin Borkowski
http://mbork.pl

Re: How to temporarily show an image in an Emacs buffer?

[Michael Heerdegen]

Marcin Borkowski <mbork@mbork.pl> writes:

> On 2023-03-08, at 05:53, Marcin Borkowski <mbork@mbork.pl> wrote:
>
> > Alternatively, it _may_ change the buffer contents but in a way that is
> > not recorded in `buffer-undo-list'.  Is that possible?
>
> I did some experimenting, and this
>
> (defvar no-undo-marker (make-marker))
> (defun no-undo-insert ()
>   "Test undo."
>   (save-excursion
>     (let ((buffer-undo-list))
>       (set-marker no-undo-marker (point))
>       (insert "this can't be undone\n"))))
> [...]

Regardless of what has already been said, just for the sake of
completeness: AFAIK the intended way to inhibit the recording of undo
is to bind buffer-undo-list to t (not to nil).

There are lots of use case in the sources - see e.g.
`image-toggle-display-text'.

Michael.

Re: How to temporarily show an image in an Emacs buffer?

[Stefan Monnier via Users list for the GNU Emacs text editor]

> I need to insert an image in the buffer in a way that doesn't interfere
> with the undo mechanism.  In other words, `insert-image' won't help me
> because (as I understand it) it needs to insert a space or some other
> string so that it can put display property on it.  How to achieve this?

`put-image` maybe?


        Stefan

Re: How to temporarily show an image in an Emacs buffer?

[Marcin Borkowski]

On 2023-03-08, at 17:41, Michael Heerdegen <michael_heerdegen@web.de> wrote:

> Marcin Borkowski <mbork@mbork.pl> writes:
>
>> On 2023-03-08, at 05:53, Marcin Borkowski <mbork@mbork.pl> wrote:
>>
>> > Alternatively, it _may_ change the buffer contents but in a way that is
>> > not recorded in `buffer-undo-list'.  Is that possible?
>>
>> I did some experimenting, and this
>>
>> (defvar no-undo-marker (make-marker))
>> (defun no-undo-insert ()
>>   "Test undo."
>>   (save-excursion
>>     (let ((buffer-undo-list))
>>       (set-marker no-undo-marker (point))
>>       (insert "this can't be undone\n"))))
>> [...]
>
> Regardless of what has already been said, just for the sake of
> completeness: AFAIK the intended way to inhibit the recording of undo
> is to bind buffer-undo-list to t (not to nil).

Thanks, I missed that.

> There are lots of use case in the sources - see e.g.
> `image-toggle-display-text'.

I didn't experiment with this, but I'm afraid that interlacing changes
to the buffer done by the user (when recording undo changes) and by the
Elisp code (while `buffer-undo-list' is bound to `t') may result in
undoing being impossible.

Anyway, I solved /my/ particular problem using overlays.  Thanks!

-- 
Marcin Borkowski
http://mbork.pl

Re: How to temporarily show an image in an Emacs buffer?

[Marcin Borkowski]

On 2023-03-10, at 17:26, Stefan Monnier via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:

>> I need to insert an image in the buffer in a way that doesn't interfere
>> with the undo mechanism.  In other words, `insert-image' won't help me
>> because (as I understand it) it needs to insert a space or some other
>> string so that it can put display property on it.  How to achieve this?
>
> `put-image` maybe?

Oh, thanks!  It looks like I reinvented it (although in a less flexible
form, sufficient for my purposes).  I guess I'll switch to `put-image'.

Best,

-- 
Marcin Borkowski
http://mbork.pl

Re: How to temporarily show an image in an Emacs buffer?

[Michael Heerdegen]

Marcin Borkowski <mbork@mbork.pl> writes:

> I didn't experiment with this, but I'm afraid that interlacing changes
> to the buffer done by the user (when recording undo changes) and by the
> Elisp code (while `buffer-undo-list' is bound to `t') may result in
> undoing being impossible.

Yes, what is allowed is very limited.  AFAIU anything changing any
positions is already very bad (undo positions are numbers, not markers).

Michael.

Re: How to temporarily show an image in an Emacs buffer?

[Marcin Borkowski]

On 2023-03-12, at 04:37, Michael Heerdegen <michael_heerdegen@web.de> wrote:

> Marcin Borkowski <mbork@mbork.pl> writes:
>
>> I didn't experiment with this, but I'm afraid that interlacing changes
>> to the buffer done by the user (when recording undo changes) and by the
>> Elisp code (while `buffer-undo-list' is bound to `t') may result in
>> undoing being impossible.
>
> Yes, what is allowed is very limited.  AFAIU anything changing any
> positions is already very bad (undo positions are numbers, not markers).

Thanks, that confirms my reservations, and shows that overlays are the
way to go.

Best,

-- 
Marcin Borkowski
http://mbork.pl

Re: How to temporarily show an image in an Emacs buffer?

[Jean Louis]

* Marcin Borkowski <mbork@mbork.pl> [2023-03-08 19:02]:
> Thanks a lot!  (Also, once I have it working, I will definitely describe
> it on my blog; I may also copy it here if someone is interested.)

I am interested in feature:

1. To temporary show image in buffer

2. To remove that image, as it was temporary shown.

Did you make functions to do that?

-- 
Jean

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Re: How to temporarily show an image in an Emacs buffer?

[Marcin Borkowski]

On 2023-03-13, at 09:29, Jean Louis <bugs@gnu.support> wrote:

> * Marcin Borkowski <mbork@mbork.pl> [2023-03-08 19:02]:
>> Thanks a lot!  (Also, once I have it working, I will definitely describe
>> it on my blog; I may also copy it here if someone is interested.)
>
> I am interested in feature:
>
> 1. To temporary show image in buffer
>
> 2. To remove that image, as it was temporary shown.
>
> Did you make functions to do that?

Not yet.  But it will be blogged about (no sooner than in April, though
– I have a buffer until the end of March).  I can mention it here, too,
unless I forget.

Best,

-- 
Marcin Borkowski
http://mbork.pl

Re: How to temporarily show an image in an Emacs buffer?

[Marcin Borkowski]

On 2023-03-13, at 09:29, Jean Louis <bugs@gnu.support> wrote:

> * Marcin Borkowski <mbork@mbork.pl> [2023-03-08 19:02]:
>> Thanks a lot!  (Also, once I have it working, I will definitely describe
>> it on my blog; I may also copy it here if someone is interested.)
>
> I am interested in feature:
>
> 1. To temporary show image in buffer
>
> 2. To remove that image, as it was temporary shown.
>
> Did you make functions to do that?

https://mbork.pl/2023-04-01_Showing_an_image_between_lines_in_Emacs

As for removing, `remove-overlays' is the nuclear option, and
`delete-overlay' a standard way to remove just one overlay (of course,
for that you need a reference to it).

Hth,

-- 
Marcin Borkowski
http://mbork.pl