[FEATURE] PDF/CBZ/CBR custom reader display double spread pages

[hollisticated-horse]

Is your feature request related to a problem? Please describe. The pdf/cbr/cbz reader doesn't have an option to display in double spread, or two pages side by side. Mentioned in #384

Describe the solution you'd like

• Add an option somewhere to have double spreads
• also define the read direction, left ← right for manga or right → left for western comics.
  • the pages view at the bottom might need to mirror this, by scrolling in the right direction.
• add subtil hint of the read direction for people not used to reading certain mediums. Could be a dark to light gradient in the background, or a border color ? Needs designing.
• add an option to set the read direction per library, if you organize per medium.

Describe alternatives you've considered n.a. maybe just having the admin options and not let the users choose ?

Additional context kavita sort of has this, but it never worked well...

[aaronleopold]

I've officially started working on this feature alongside https://github.com/stumpapp/stump/issues/384. So far, the behavior will be as follows:

• You may configure default settings for the reader(s) as part of library settings. Any book without overrides will default to these settings
• You can override settings on a per-book basis when you are in a reader (via the toolbar). The overrides are persisted to your client only, they are not synced to the DB
  • There will be options in settings to clear any local configurations
• The initial set of options which may be configured will be:
  • Double spread (has no effect on continuous scrolling)
  • Reading direction (ltr or rtl, also has no effect on continuous scrolling)
  • Image height/width sizing (see #437)
• If a user doesn't like these settings, they currently have to override them for each book. I haven't come up with a solution for this yet, and might punt it to after the initial effort

I'm focused on the functionality for now, as it will be a solid chunk of work. I can post an update with what it looks once it is properly designed. If you (or any onlookers) have thoughts, feel free to share

[aaronleopold]

Tentative designs