Add custom parser to DragValue and Slider, with additional support for binary, octal, and hexadecimal numbers.

[Adanos020]

Closes #1953.

Adds a custom_parser method to DragValue and Slider, along with extra binary_u64, octal_u64, and hexadecimal_u64 which overwrite the custom_formatter and custom_parser.

The purpose of custom_parser is to convert the text input from both widgets to a f64. A parser function returns an Option<f64> set to Some when parsing succeeds or None when it fails.

Additional methods for different number systems all take in a min_width parameter that specifies the minimum number of displayed digits. If the number is shorter than min_width, it will be prefixed with additional 0s to match it. hexadecimal_u64 also takes in a bool which specifies if in the output text alphabetic digits should be uppercase or not.

Demo (apologies for quality):

Code for the demo:

ui.add(
    egui::Slider::new(&mut self.age, 0..=1023)
        .text("bin")
        .binary_u64(10),
);
ui.add(
    egui::Slider::new(&mut self.age, 0..=1023)
        .text("oct")
        .octal_u64(4),
);
ui.add(
    egui::Slider::new(&mut self.age, 0..=1023)
        .text("hex")
        .hexadecimal_u64(3, false),
);
ui.add(
    egui::Slider::new(&mut self.age, 0..=1023)
        .text("HEX")
        .hexadecimal_u64(3, true),
);
ui.add(
    egui::Slider::new(&mut self.age, 0..=((60 * 60 * 24) - 1))
        .text("time")
        .custom_formatter(|n, _| {
            let n = n as i32;
            let hours = n / (60 * 60);
            let mins = (n / 60) % 60;
            let secs = n % 60;
            format!("{hours:02}:{mins:02}:{secs:02}")
        })
        .custom_parser(|s| {
            let parts: Vec<&str> = s.split(':').collect();
            if parts.len() == 3 {
                parts[0]
                    .parse::<i32>()
                    .and_then(|h| {
                        parts[1].parse::<i32>().and_then(|m| {
                            parts[2]
                                .parse::<i32>()
                                .map(|s| ((h * 60 * 60) + (m * 60) + s) as f64)
                        })
                    })
                    .ok()
            } else {
                None
            }
        }),
);

[Mingun]

May be return a Result<T, String> where the Err variant will represent a text that can be shown to the user why his input is incorrect? For now egui can just use .ok() and not shown anything, but in the future it could.

[Adanos020]

May be return a Result<T, String> where the Err variant will represent a text that can be shown to the user why his input is incorrect? For now egui can just use .ok() and not shown anything, but in the future it could.

If we do want this, I think Result<T, Option<String>> would be better as it'd give you the option not to have an error message.

It wouldn't make sense to change it in this PR though, since there isn't yet a way to display an error message from a parser, which itself is a whole different feature. The current implementation of DragValue discards the error from str::parse anyway, so I think it's best to leave this for later.

[emilk]

nice!

[emilk]

May be return a Result<T, String> where the Err variant will represent a text that can be shown to the user why his input is incorrect? For now egui can just use .ok() and not shown anything, but in the future it could.

Let's wait with that until we actually implement showing the errors (if ever)

[Adanos020]

Applied suggested changes, also added a twos_complement flag to give the choice whether you want to display negative numbers with a - sign or in the 2's complement representation.

[enomado]

Would be awesome to add thousands separator, e.g. 1,000,000.0

[Adanos020]

Would be awesome to add thousands separator, e.g. 1,000,000.0

@enomado Right now you can do it with num_format and custom_formatter I added in #1851, it's available in v0.19 😄

use num_format::{Locale, ToFormattedString};
ui.add(DragValue::new(&mut n).custom_formatter(|n, _| n.to_formatted_string(&Locale::en)));