Re: Multi image PDF continuous mode

[Juri Linkov <juri@linkov.net>]

> 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,
> 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.

One problem is that the vertical scroll bar doesn't allow scrolling all images.

>> Maybe then after a real image
>> will be scrolled out of view, it could be replaced with a placeholder again
>> to free memory.
>
> Haha, that is exactly what I meant with exactly that (the following)
> sentence.

This is nice that you already took care about this case.

>     > 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.