New package image-roll! Improved document display engine providing continuous scrolling.

[Here](https://github.com/dalanicolai/image-roll.el) is a new package providing improved continuous scrolling in pdf-tools and doc-view (please read [instructions](https://github.com/dalanicolai/image-roll.el#image-rollel) first). This is the successor of the [pdf-continuous-scroll package](https://github.com/dalanicolai/pdf-continuous-scroll-mode.el). Making it a new package (instead of an update), was necessarry because this package provides a general 'display engine' which can be used also by other packages, like doc-view. Besides having extracted the 'display functionality' into a separate package, the code and functionality of the engine has been simplified, so that it is (even) easier to understand and maintain, and also it should increase compatibility with complementary packages (like pdf-tools and doc-view). The engine works very fine, although I would be very happy if anybody has an idea for a solution of the remaining (minor) issue [described in the README](https://github.com/dalanicolai/image-roll.el#issues). It seems to be working quite well also with most/all `pdf-tools-modes`, although it is not straightforward to make everything work flawlessly. Despite, the minor issues, I guess it works quite fine already for most people. Happy scrolling!

Great package! Have you tried sending an email in the mailing list to raise the awareness about the problem you are observing? I believe there may be someone who can help you there.

>Great package! Thanks! I have indeed mailed to the mailing list (link is in the README). But this morning I have additionally sent a [feature request](https://lists.gnu.org/archive/html/emacs-devel/2022-05/msg00032.html). Let's see if the easy fix will be possible.

Very nice, I hope some users with intact socks donate!

As long as the socks are intact, I am happy ;)

There is [an answer](https://lists.gnu.org/archive/html/emacs-devel/2022-05/msg00032.html) already, and the issue has been fixed

Thank you for working on this! This package sounds very promising. I tested image-roll.el with your pdf-tools-fork on vanilla Emacs, unfortunately, the "minor issue" came up very often/regularly. I experienced a lot of blanked out pages. I hope you can sort this out soon. Thanks again! Please keep us posted.

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>Thank you for working on this! This package sounds very promising. Thanks! Although I answered [here](https://www.reddit.com/r/emacs/comments/uhcuhy/comment/i79mwud/?utm_source=share&utm_medium=web2x&context=3) that it had been fixed, I accidentally pushed (the pdf-tools part of) the fix to the wrong repo (I fixed it while I was very much in a hurry). Anyway, I have pushed the fix to the correct repo now. I hope, most or all, of the occurrences of the 'minor' issue have been 'eliminated' (fixed). Please update both the image-roll and the pdf-tools (and if used, also the doc-view) packages and try again.

Good to hear, I will test it tomorrow. Very happy that you work on this capability!

To clarify, this does something different from iscroll. https://github.com/casouri/iscroll

Thanks a lot for the package! I was testing and it mostly was working fine, except that when I press space or scroll down to the next page, it emits this error message: >image-display-size: Invalid image specification: (space :width (970) :height (1259)) It is also there with emacs -Q. I am using emacs 29.0.50. Is this error expected?

Thanks for this reply. That error is indeed expected. I should have mentioned that I have only added keybindings under the arrow keys (up/down) and next/prior keys (PgUp/PgDown). Additionally there are the S-prior/S-next to scroll forward/backward a full screen. As I am a Spacemacs user, I have bound the functions that are used for scrolling in Spacemacs, which are `pdf-view-next-line-or-next-page` (and its previous version). It looks like pressing space usually should scroll a near full screen. You can scroll a full screen forward using S-next (Shift-PgDn). You could bind that command to space if you like.

Makes sense. Thanks!