#221 Canvas displayed on a second screen

[Theo Kluter]

Hi all,
I use xournal almost daily in my teaching activity and found that it would be awsome to have following feature:
Current situation:
I use my X1 tablet in mirror mode to be able to see on my screen and that the students see it on the beamer (second screen). However, as each beamer is different I all the time have to calibrate the wacom table which is kind of anoying.
Nice to have:
I would be great if there is a feature in xournal where only the active canvas can be "cloned" on the second screen, meaning that the main xournal window is on the primairy screen and the canvas (without the toolbars, etc.) is "duplicated" on the second screen. This is for example implemented in pdfpresenter.

I would be very interested to help implement this functionality, but have no clew on complexity and where to start.

Any sugestions/help would be appreciated.

[Denis Auroux]

This is essentially impossible to implement cleanly in "the right way" with xournal's current code structure. It is also difficult to implement it in a way that allows for everyone's different ideas of how this should work (does the second screen display exactly the same view as the main one, or does it show a potentially different view of the document (another zoom level etc). But it can be done in a "dirty" way and has been done.

One version of this feature has been implemented by Axel Kittenberger in 2016, the patch can be found as an attachment to this message:
https://sourceforge.net/p/xournal/mailman/message/35077147/
It should apply more or less cleanly to the current code (or else you can get the git version from that time, there haven't been much in the way of changes since).
I can't incorporate this patch into the official code tree because duplicating essentially all of the rendering code is clearly not a sustainable approach for implementing such features, even though it is the fastest way to do it just once.

Denis