How to find out whether an image is displayed anywhere?

How to find out whether an image is displayed anywhere?

[Lars Magne Ingebrigtsen]

I just noticed that animated images keep on being animated even if the
images themselves aren't displayed in any buffer.

That seems wrong.

Is there a way to query Emacs whether an image is actually displayed
anywhere?  I looked through image.el, and I couldn't find anything...

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

Re: How to find out whether an image is displayed anywhere?

[Chong Yidong]

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

> I just noticed that animated images keep on being animated even if the
> images themselves aren't displayed in any buffer.
>
> That seems wrong.
>
> Is there a way to query Emacs whether an image is actually displayed
> anywhere?  I looked through image.el, and I couldn't find anything...

AFAIK there is no way to check this right now.  Image lookup is
performed as needed during redisplay.

Re: How to find out whether an image is displayed anywhere?

[Lars Magne Ingebrigtsen]

Chong Yidong <cyd@stupidchicken.com> writes:

> AFAIK there is no way to check this right now.  Image lookup is
> performed as needed during redisplay.

Then I guess Gnus will have to explicitly stop any animation going on in
the article buffer when de-selecting an article.  (I.e, loop over
`image-animate-timer' for the images first and cancel them.)

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

Re: How to find out whether an image is displayed anywhere?

[Stefan Monnier]

> Is there a way to query Emacs whether an image is actually displayed
> anywhere?  I looked through image.el, and I couldn't find anything...

There is a way: fontification-functions (aka "jit-lock").  It's a bit
round-about, but with enough work it should be possible to use it for
that purpose (e.g. use a timer to remove the `fontified' property every
N seconds and if it's still nil after an additional M seconds, then turn
off animation.  Or maybe better: after the animation timer fires don't
change the image yet but instead only remove the fontified property and
then change the image from fontification-functions).


        Stefan

Re: How to find out whether an image is displayed anywhere?

[Lars Magne Ingebrigtsen]

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

> Or maybe better: after the animation timer fires don't
> change the image yet but instead only remove the fontified property and
> then change the image from fontification-functions).

I'm not familiar (at all) with the jit-lock functions, but if you think
that's possible, I'm all for it.  :-)  But I'm not the person to
implement something like that.

It sounds like it could be kept nicely local to image.el, though, so the
users of the animated pictures don't have to care.

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

Re: How to find out whether an image is displayed anywhere?

[Stefan Monnier]

>> Or maybe better: after the animation timer fires don't
>> change the image yet but instead only remove the fontified property and
>> then change the image from fontification-functions).

> I'm not familiar (at all) with the jit-lock functions, but if you think
> that's possible, I'm all for it.  :-)  But I'm not the person to
> implement something like that.

> It sounds like it could be kept nicely local to image.el, though, so the
> users of the animated pictures don't have to care.

Indeed.  It would look something like:

- change the code that updates the image so that instead of actually
  updating the image, it just sets a `image-upon-redisplay-function'
  text-property on the image, whose value is a function that actually
  updates the image.
- call (jit-lock-register #'image-update-animations) somewhere.
- write image-update-animations which just looks for the
  image-upon-redisplay-function properties in the specified region and
  calls the corresponding function.

There are still some issues with respect to timer management (you may
want not to use a repeating timer but instead to re-arm the timer
manually from the image-upon-redisplay-function).


        Stefan