Add option to customize progress bar rounding

[YgorSouza]

The minimum filled width is adapted to the radius and the animation is disabled so it renders correctly.

[YgorSouza]

To test, add e.g., .rounding(2.0) here:

egui/crates/egui_demo_lib/src/demo/widget_gallery.rs

Lines 196 to 198 in eb0812a

	let progress_bar = egui::ProgressBar::new(progress)
	.show_percentage()
	.animate(*animate_progress_bar);

Should I add this somewhere in the demo?

[YgorSouza]

I'm thinking that instead of setting an explicit rounding value, it could instead be a boolean that makes it use the same rounding as the other widgets, like buttons and textboxes, so it is easier to keep the UI consistent. Does that make sense? I also have to fix some visual bugs at low fill percentages before this is ready to merge.

Edit: actually, the way it is currently might be better, as you can just set the rounding to one of the ui settings if you want, e.g., ProgressBar::new(progress).rounding(ui.visuals().noninteractive().rounding)

[emilk]

It would be nice with a image or gif for this!

[YgorSouza]

It would be nice with a image or gif for this!

Screencast.from.2023-11-10.23-25-49.webm

[emilk]

why only look at sw and nw here? Wouldn't it make sense to use something like rounding.max() instead?

[YgorSouza]

Since this min_width is meant to make the rounding look right when the progress bar is empty, I figured only the left side mattered. But maybe it would be better to just use max(). I'll do a quick test and commit it.

[YgorSouza]

So there is no method Rounding::max currently. Should I add one?

It doesn't seem to be necessary, though. The problem this min_width avoids is that the filled rect is flattened when it is too small, and then it ends up appearing outside the background rect, like this:

Actually, if there was a way to avoid this overflow without setting a minimum width, I think a lot of people would prefer that (see for example #3999). But I don't know if it's possible.