Okay, so I have got a working Proof of Concept / core functionality.
You can very easily test it by loading the bookroll.el file from here
<https://github.com/dalanicolai/bookroll.el>,
then do `M-x br-test` and scroll using `j`/`k`. I will now focus on trying
to implement
it into pdf-tools, which is probably a little more work as its code is
quite complex/opaque.

@Juri
```
Maybe then after a real image
will be scrolled out of view, it could be replaced with a placeholder again
to free memory.

> Then, the scrolling can be implemented, by changing the display
properties (from empty
> svg to real image, and back)
```

Haha, that is exactly what I meant with exactly that (the following)
sentence.
Anyway, thanks for the nice response!


On Sat, 8 Jan 2022 at 19:33, Juri Linkov <juri@linkov.net> wrote:

> > I would like to share my perspective on this, but before I do that,
> > let me first ask you if you have any idea about why pdf-tools is not
> part of
> > Emacs. It is a very high quality package, that already lazily loads the
> images,
> > and provides many sophisticated features.
>
> It would be nice to include pdf-tools in Emacs, but I don't know
> if the new maintainer has an intention to submit it for inclusion.
>
> > You might already be familiar with my 2-buffer continuous scroll hack
> for it
> > (which can be easily ported to doc-view mode, but 'developing' a 'real'
> > continuous scroll mode solution makes much more sense
>
> I agree, a real continuous scroll mode would be more preferable.
>
> > - I have created a, very rude but already nicely working, 'real'
> continuous
> >   scroll proof of concept, for which, if you are interested, you can
> find the
> >   code in this commit. It currently uses a trick where it only uses two
> images
> >   at the time
>
> While two-images approach could provide better optimization for memory,
> it has severe limitations, e.g. the vertical scroll bar can't be used
> to scroll all images at once.
>
> >   but as I will describe now, I think it will be better to create a
> >   'bookroll' package for it.
>
> This is a promising direction.
>
> > I think the bookroll should not be so difficult to implement (I first
> started to
> > think about a general 'image-roll', but I think continuous scrolling is
> > generally not what you want for viewing/scrolling images
>
> Why not?  'image-roll' could be useful for the image gallery packages
> like image-dired.el and thumbs.el.
>
> > So my current idea for how to implement it, is by
> > immediately creating overlays for all pages in a single buffer and fill
> them
> > with 'empty' svg-images of the correct size (after testing this with a
> thousand
> > 'placeholders', it seems that the 'empty' images use almost no memory).
>
> Good news, so loading a 1000-page document won't take much memory.
> Only scrolling will load real images.  Maybe then after a real image
> will be scrolled out of view, it could be replaced with a placeholder again
> to free memory.
>
> > Then, the scrolling can be implemented, by changing the display
> properties (from empty
> > svg to real image, and back) and jumping to the correct positions using
> > `set-window-vscroll`. I have started on writing bookroll.el, of course
> your
> > joined efforts or feedback would be very much appreciated. Otherwise,
> this short
> > message serves just to inform you about these activities.
>
> Thanks, feel free to post updates about your progress
> or when stuck on some problems.
>