Redone #4189, working preview scrolling

[GNUSheep]

Finally redone preview scrolling on current master. Works pretty fine.

I used code from: @Manosmer, and make it work with current version of helix.

Closes #4102

[thomasaarholt]

Current keybindings:

• alt-j / shift-down - Move preview down scroll-lines at a time
• alt-k / shift-up - Move preview up scroll-lines at a time
• alt-d - Move preview down half height of the preview area
• alt-u - Move preview up half height of the preview area
• alt-f / alt-PageDown - Move preview down one full preview area height
• alt-b / alt-PageUp - Move preview up one full preview area height

Originally posted by @EpocSquadron in #4189 (comment)

[thomasaarholt]

I do observe that when scrolling, the syntax highlighting does not update. Only the text first shown in the preview pane is syntax highlighted.

[GNUSheep]

@thomasaarholt

Hi! Thank you for your help. I fixed my mistakes, and now all should work well.

My only concern is about keybinding alt-PageUp, because as mentioned before:

I'm not 100% certain alt- is valid with PageUp/PageDown in terminals, but worth a try.

I tried the above on iTerm2 without success. Therefore, I did not include those keybindings. It might be a limitation just on my platform though.

In my case alt-PageDown works pretty fine, but alt-PageUp doesn't.
I tested on alattracity, and gnome terminal and got same result.

But as mentioned above it might be just a limitation on my platform.

[GNUSheep]

@archseer
@the-mikedavis

[EmrysMyrddin]

I've tried it, works very well, very welcomed addition ! I hope it will be merged soon :-)

[EmrysMyrddin]

I'm using Helix based on your PR, and I came across another issue:

Here the diagnostic is miss-rendered. It should not underline the whole comment.

Here how it looks in the main buffer:

Note: the diagnostic is rendered in the preview only if the file have been opened at least once since Helix started.

[David-Else]

@thomasaarholt

My only concern is about keybinding alt-PageUp, because as mentioned before:

I'm not 100% certain alt- is valid with PageUp/PageDown in terminals, but worth a try.

I tried the above on iTerm2 without success. Therefore, I did not include those keybindings. It might be a limitation just on my platform though.

In my case alt-PageDown works pretty fine, but alt-PageUp doesn't. I tested on alattracity, and gnome terminal and got same result.

But as mentioned above it might be just a limitation on my platform.

I am not a fan of using the Alt key, particularly with the Alt + PageUp/PageDown combinations. I have noticed that currently, PageUp/PageDown seems to jump up and down the file or item list by a seemingly random amount in different pickers. I really can't find a good use for the current functionality in the picker. It would be better to use PageUp/PageDown for preview scrolling instead, similar to how LazyGit does. Now that we have Pickers v2, it makes more sense to refine the search rather than scrolling through the list of items in such large increments.

[GNUSheep]

@EmrysMyrddin

Hi! Thank u for using helix based on my PR.
I fixed that bug,
(I just forgot to change offset.anchor in doc_diagnostics_highlights)

If u find more bugs I will be happy to fix them :)

[GNUSheep]

@David-Else
Hello! Looking at the code PageUp and PageDown, moves up or down by a exactly one page. But I agree with you that it is not so useful, I think that many people just search by using search bar rather than scrolling up.

Using just PageUp or PageDown seems like nice idea.

[GNUSheep]

@archseer @the-mikedavis @pascalkuthe