Strip.apply_style misses post_style parameter for Segment.apply_style

[jbdyn]

Hi,

I wanted to redefine the render_line method of a widget to alter the style of strips returned by the superclass method.

However, my Styles are not applied when calling Strip.apply_style.

The problem is that Strip.apply_style does not expose the post_style parameter to be passed to rich's Segment.apply_style. Its docstring in turn says

Returns an iterable of segments where the style is replaced by style + segment.style + post_style

Without the post_style parameter in Strip.apply_style, I have no way to overwrite the style of a Strip if an internal Segment comes with its own style.

Since I am not a collaborator in this project: A fix is available on my fork at https://github.com/jbdyn/textual/tree/apply-post-style with commit 594265f.

If this patch is not suitable: What would be the alternative if I wanted to change a Strip returned by the superclass's render_line method?

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[jbdyn]

A workaround would be to iterate over a Strip to get its segments and apply the style to those individually:

from rich.style import Style
from textual.strip import Strip

class ...
   def render_line(self, y: int) -> Strip:
       # strip from superclass
       strip = super().render_line(y)

       # my custom style I want to see applied
       my_style = Style(bgcolor="red")

       # iterate over the segments of the strip and
       # apply styles to them
       segments = [seg for seg in strip]
       segments = Segment.apply_style(segments, post_style=my_style)

       # recombine to newly styled strip
       return Strip(segments)

However, this functionality of iterating over a Strip is not exposed in the documentation.

[nightcityblade]

Hi, I'd like to work on this. I'll submit a PR shortly.

[willmcgugan]

@jbdyn post_style is your proposed solution to a problem. I would like to understand your problem before I can be sure your fix is the best one.

What is it that you are rendering, and what are you attempting to change in your render_line method? Please explain at a higher level, as though you weren't familiar with the Strip / Segment internals.

[jbdyn]

@willmcgugan Sure!

I inherit from the TextArea widget to add real-time collaboration functionality.

The API is mostly there and works, so I can update the content from both local and remote, but I also need to render the remote cursor positions.

For that, my current solution is to implement my own render_line method altering the output strip of TextArea.render_line. I apply a distinct background color to the cell where the remote cursor sits.

I wanted to do this with Strip.apply_style, but the background color does not get applied:

# from `TextArea` widget
strip = super().render_line(y)

# define style for remote cursor
cursor_style = Style(bgcolor=cursor_color)

# cut the current strips at the remote cursor position
strips = strip.divide([cursor_start, cursor_end])

# apply remote cursor style to remote cursor cell;
strips[1] = strips[1].apply_style(cursor_style)  # <-- does not change the bgcolor

# rejoin for rendering 
strip = Strip.join(strips)

As it could be relevant in this context, in the future, I also would like to not just color a cursor position but the whole selection between the anchor and head of a remote cursor.

If it helps, here is the code.

[willmcgugan]

I think you would be better off doing this in the get_line method, which returns a Rich Text object. You can apply a style to a single cell with Text.stylize, and it will be more efficient to render than post processing Strips...

[jbdyn]

Sounded nice and I tried, but I ran into three problems:

1. With Text.stylize I cannot paint cursors at the end of a line, i.e. behind the content of Text. Padding cannot be used here as it alters the content. I cannot see a solution to that.
2. The background color of remote cursor cells gets overwritten by the highlighting of the line the own (local) cursor is currently in. I could turn off highlighting, but that feels like getting off too lightly.
3. The get_line seems to be used in combination with some caching: I refresh the UI with TextArea.refresh when a cursor position has changed, but the remote cursor highlighting only changes when also the content of the line with the remote cursor changed. Simple remote cursor movements - without changing the content - are not reflected as get_line does not even get called.

[willmcgugan]

get_line may not be the right point then, but there should be a point prior to rendering where you have a Text object that spans the width of the window.

Consider Strips to be the Textual equivalent of a bitmap. You want to add your cursors at an earlier stage where you can work with a more semantic layer. Have a look at _render_line. At some point in that quite large method there should be a Text object you can highlight any cell you wish.

Try copying that method to a subclass and add your cursor code. I'd also accept a PR to add a method to provide a convenient hook.

[jbdyn]

The local cursor/selection is also drawn in the _render_line method.

As I basically want to do the exact same for multiple cursors: Would you also be interested in a PR which puts the selection drawing code in a public method, say, draw_selection, so that I can overwrite that for multiple cursor and multi-cursor support? I could then use the single-cursor-drawing method via super().draw_selection.

A style hook could then still be implemented, but that does not exactly hit my case.