Adding and removing CodeMirror instance on-demand, i.e. depending on …

[luis-mueller]

…the visibility of a cell - #291.

Hi all,

I took on the enhancement in #291 by only creating the CodeMirror instance if a cell is hidden (folded) and deleting the instance upon folding/hiding the cell.

I introduced a new boolean called cm_enabled that is basically !is_hidden, but allows to later add more conditions (e.g. "is cell visible on screen" - that was probably meant by viewport, right?).

The general idea is then to, instead of as before running the effect hook that set up the CodeMirror only with initial values, re-run the effect hook everytime cm_enabled changes and to wrap everything else that requires the instance into an IF that checks for cm_enabled.

This is my first contribution to this project and I hope you like it - if you have any suggestions or concerns, I'd be happy to discuss.

If this first step is done, I'd be happy to also take on the viewport-idea.

[fonsp]

Strangely I am measuring no performance benefit... I tested on:
https://github.com/fonsp/disorganised-mess/blob/master/big.jl

It does however fix a codemirror glitch when unfolding a cell, so I'm happy 🙃

[fonsp]

Thank you! 🌈