Re: excessively slow image animation

[Evgeny Zajcev <lg.zevlg@gmail.com>]

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ср, 13 февр. 2019 г. в 20:03, Lars Ingebrigtsen <larsi@gnus.org>:

> Evgeny Zajcev <lg.zevlg@gmail.com> writes:
>
> > I've got multi frame image at http://lgarc.narod.ru/giphy.mp4
> >
> > And run next code on it:
> >
> >   (let ((ctime (float-time)))
> >     (setq img (create-image "~/tmp/giphy.mp4" 'imagemagick nil :scale
> 1.0))
> >     (insert-image img)
> >     (cl-dotimes (index 65)
> >       (image-show-frame img index 'nocheck)
> >       (sit-for 0.0))
> >     (- (float-time) ctime))
> >   ==> 18.788017988204956
> >
> > 18 seconds to show every frame
>
> Wow, that's slow...
>
> [...]
>
> > Now I use method with bmp files.  I would like to use built in `:index'
> image
> > property to animate images, however current animation speed is totally
> not
> > acceptable.  Can this be fixed, or am I doing something wrong?
>
> If I remember correctly, I was the one that added the :index support for
> imagemagick images in Emacs.  It's quite likely that I was using
> non-optimal ways to do the animation and that imagemagick has better and
> faster ways of doing the computation.
>
> Have a look at imagemagick_compute_animated_image in image.c and rewrite
> to be faster.  :-)
>

The problem is that IM always decodes multi frame images to the last image
uppon MagickReadImage.  In this example it takes ~0.2 seconds (as time on
convert command shows), so just loading time without pixel operations, etc
would take 0.2*65=13 seconds

Animation code always do MagickReadImage uppon loading image, even if there
is cached wand.

Probable solution would be to use some other signature for the cache
(md5sum on blob, or md5sum on file, or maybe just the filename!)

In this case we can just get the wand from the cache, without calling
MagickReadImage on `:index' change

-- 
lg

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