Add the ability to customise scrollbar bar segments

[mon]

Currently, the characters that make up a scrollbar are hardcoded. It would be nice if they could be overridden. Personally, I need to support poor fonts, so need to replace missing glyphs. But it would be neat to use braille characters for a unique style.

Thoughts on making them a classvar, so they can be monkeypatched in for now? I can do that PR if it's an OK change.

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[willmcgugan]

You can patch in a new scrollbar renderable as follow:

from textual.scrollbar import Scrollbar

ScrollBar.renderer = MyScrollbarRenderer

Have a look at how the original is implemented. You can copy that and customize it.

[mon]

For sure! I was just hoping for an easier way than duplicating the ~72 line render function. Textual is still developing pretty quickly, and I'm wary vendoring too much of its code to fix things.

[davep]

@mon For what it's worth, the scrollbar renderer has been in place for well over a year, has been stable as far as I can remember, and is part of the documented API.

[willmcgugan]

Yeah, that's not going to change. Textual's API is quite stable now.

[mon]

That's good to know! I guess then - would a PR changing the bar glyphs to be a classvar be rejected? I still do like the idea of a 3-line way to modify the class.

[willmcgugan]

I think that would be reasonable. Happy to accept a PR.

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