feat(bar): Add support for custom icons

[NSPC911]

You can now super a textual.renderable.bar.Bar class and change HALF_BAR_LEFT, BAR, and HALF_BAR_RIGHT, before passing the class as a keyword argument in the textual.widgets.ProgressBar widget as bar_renderable. The keyword arg's name might be weird.

resolves #5350

Image:

Code Snippet

from textual.app import App, ComposeResult
from textual.renderables.bar import Bar as BarRenderable
from textual.widgets import ProgressBar
from textual.color import Gradient
class SignsRenderable(BarRenderable):
    HALF_BAR_LEFT = "-"
    BAR = "="
    HALF_BAR_RIGHT = "-"
class ArrowsRenderable(BarRenderable):
    HALF_BAR_LEFT = ">"
    BAR = "="
    HALF_BAR_RIGHT = ">"
class ThickBarRenderable(BarRenderable):
    HALF_BAR_LEFT = "▐"
    BAR = "█"
    HALF_BAR_RIGHT = "▌"
class SlashBarRenderable(BarRenderable):
    HALF_BAR_LEFT = "\\"
    BAR = "|"
    HALF_BAR_RIGHT = "/"
class Application(App):
    DEFAULT_CSS = """
    .bar--indeterminate { color: #bf616a !important; background: #2e3440 !important }
    """
    def compose(self) -> ComposeResult:
        gradient = Gradient.from_colors("#8fbcbb", "#88c0d0", "#81a1c1", "#5e81ac")
        for widget in [ThickBarRenderable, SignsRenderable, SlashBarRenderable, ArrowsRenderable]:
            yield ProgressBar(bar_renderable=widget, gradient=gradient)
        yield ProgressBar(gradient=gradient)
    def on_mount(self) -> None:
        self.progress_timer = self.set_interval(1 / 10, self.make_progress, pause=True)
        self.set_timer(4.0, self.start_progress)
    def start_progress(self) -> None:
        for bar in self.query(ProgressBar):
            bar.update(total=100)
        self.progress_timer.resume()
    def make_progress(self) -> None:
        for bar in self.query(ProgressBar):
            bar.advance(1)
Application().run()

Please review the following checklist.

• Docstrings on all new or modified functions / classes
• Updated documentation
• Updated CHANGELOG.md (where appropriate)

[willmcgugan]

Not convinced this is something that warrants being in the constructor. It feels more like an internal detail than configuration.

How about we expose the bar renderable as a classvar?

Something like this:

class FancyProgress(ProgressBar):
    BAR_RENDERABLE_CLASS = FancyBar

Then you wouldn't have to specify it everywhere you use the progress bar.

[NSPC911]

If the bar renderable is passed in as a class variable into the Bar element, what about the main ProgressBar element?

I'm not sure how the ProgressBar element can receive the Bar Renderable to be passed to the Bar widget as a class variable before being rendered

[NSPC911]

I'm also a tad bit confused on the comment, because your review comment is on the Bar element while your code example is for the ProgressBar element