What is the easiest way to add a font size slider without using egui.settings?

[NadyaNayme]

I'm a beginner to Rust - as in maybe a week into things now. Every existing issue/discussion I've found points to long out-of-date examples that have since changed. I've tried following the breadcrumbs and ended up short. I don't want to add my own fonts and I can't figure out how to persist the egui.settings font size sliders because I can't figure out how to access or set that value. All I want is for people to be able to bump up the much-to-small-by-default font size for accessibility reasons.

I'm sure I've passed over the documentation to do exactly what I want to do several dozen times now but at this point my brain has shut off. I've currently resorted to scaling the entire UI with ctx.set_pixels_per_point but this is less-than-desirable because it also scales my 32x32 icons and those become blurry when scaled so I want to do things properly.

[coderedart]

There's three things to remember.

1. Font Family which is either proportional (for normal text), monospace (for numbers in dragvalue ) or some custom thing with a custom name.
2. Font Id which is just a Font Family (above) + Font size.
3. TextStyle which is just an easy enum for small, monospace, heading, normal or any custom text styles

to set custom size for all text styles:
Style just has a Map<TextStyle, FontID>. so, you can just get style with ctx.style(), clone the style, set the sizes you want by

for (_text_style, font_id) in style.text_styles.iter_mut() {
    font_id.size = 24 // whatever size you want here
}

you can remember user preferences for all default text styles

   Small,
    Body,
    Monospace,
    Button,
    Heading

, and just set the sizes for those text styles with style.text_styles.get_mut(TextStyle::Small).unwrap().size = 24.

to instead just set a single font for everything, style also has a override_font_id field. just set that field with style.override_font_id = Some(FontID::proportional(24)); // whatever size you want to use that size as default for all widgets.

once you are done setting font size either way, you just need to tell egui to use that style with ctx.set_style() and that should work.

I can't really test that code at the moment, but that is the rough sketch.

you can also just use ctx.style_ui to just use the egui provided UI, then serialize or deserialize the style into json or something to store it. that's how I do it in my app to support "user themes" which they can share with each other. (given they also share their fonts with each other, but you don't use custom fonts anyway)

[NadyaNayme]

I really do appreciate this writeup and it clarified with me that my understanding was fuzzy at the edges but mostly right.

This is roughly as far as I got but I couldn't get the code to work because I had no idea what to actually do with style.text_styles or how I was meant to get the TextStyle I wanted to modify. I was messing around with some of the example code you gave to try it to compile and got stuck with a compiler issues regarding Arc and Deref - turns out I was meant to *ctx.style() as shown by emilks code.

With my reading of this help text though - I would never in a million years had tried to deref the Arc because it was telling me it wasn't implemented for Arc - though I'm nearly positive I'm misreading or misunderstanding the message.

However emilk's example code from below worked - swapping out the hard coded values with my config values using the below block:

    let mut style = (*ctx.style()).clone();
    style.text_styles = [
        (Heading, FontId::new(30.0, Proportional)),
        (Body, FontId::new(18.0, Proportional)),
        (Monospace, FontId::new(14.0, Proportional)),
        (Button, FontId::new(14.0, Proportional)),
        (Small, FontId::new(10.0, Proportional)),
    ]
    .into();
    ctx.set_style(style);

Works like a charm! My users thank you emilk :) 👍

[emilk]

There is an example for this coming in a PR: https://github.com/emilk/egui/pull/1476/files