Add display precision to diagnostics

[liamcurry]

What problem does this solve or what need does it fill?

Diagnostics have no concept of display precision, so values for all diagnostics are displayed using a hard-coded static precision of 6 in the LogDiagnosticsPlugin:

bevy/crates/bevy_diagnostic/src/log_diagnostics_plugin.rs

Lines 65 to 75 in 2b80a3f

	"{name:<name_width$}: {value:>11.6}{suffix:1} (avg {average:>.6}{suffix:})",
	name = diagnostic.name,
	suffix = diagnostic.suffix,
	name_width = crate::MAX_DIAGNOSTIC_NAME_WIDTH,
	);
	return;
	}
	}
	info!(
	target: "bevy diagnostic",
	"{name:<name_width$}: {value:>.6}{suffix:}",

What solution would you like?

A new field could be added to bevy_diagnostic::Diagnostic, pub precision: usize:

bevy/crates/bevy_diagnostic/src/diagnostic.rs

Lines 34 to 42 in 2b80a3f

	pub struct Diagnostic {
	pub id: DiagnosticId,
	pub name: Cow<'static, str>,
	pub suffix: Cow<'static, str>,
	history: VecDeque<DiagnosticMeasurement>,
	sum: f64,
	max_history_length: usize,
	pub is_enabled: bool,
	}

What alternative(s) have you considered?

Instead of handling value formatting manually in plugins with format!, Diagnostic could alternatively provide a formatting function to format values. A new field could be added to bevy_diagnostic::Diagnostic, pub formatter: Arc<dyn (Fn(f64) -> String) + Send + Sync>.

This approach would give maximum flexibility, but it does incur the (possibly minimal) runtime performance cost of dynamic dispatch.

Additional context

This is relevant for a plugin I'm working on to dynamically visualize diagnostics.

https://github.com/sagan-software/bevy_diagnostic_visualizer

[alice-i-cecile]

IMO we can get away with a simpler solution here. I think just allowing users to configure the display precision on a per-diagnostic basis would work totally fine.

[liamcurry]

@alice-i-cecile do you mean configured as part of the LogDiagnosticsPlugin or somewhere else?

[zeroacez]

I have never contributed before and would like to help out. Do you think I can do something here?

[alice-i-cecile]

@alice-i-cecile do you mean configured as part of the LogDiagnosticsPlugin or somewhere else?

This could work. I think it makes more sense when adding diagnostics here:

bevy/examples/diagnostics/custom_diagnostic.rs

Line 27 in deb07fe

diagnostics.add(Diagnostic::new(

@zeroacez yes, absolutely! Feel free to dive in and open a draft PR :) If you have any questions, feel free to either ask here, on your PR or on Discord and folks will be more than happy to help with either Rust, Bevy or Github questions you may have.