The Flex widget has been added to the fltk crate, under the group module. This repo mostly now serves the purpose of providing examples of usage!
A Rust port of FL_Flex, which provides a flexbox widget for FLTK.
[dependencies]
fltk = "1.2"
fltk-flex = "0.2"
use fltk::{prelude::*, *};
use fltk_flex::Flex;
fn main() {
let a = app::App::default().with_scheme(app::Scheme::Gtk);
let mut win = window::Window::default().with_size(400, 300);
let mut flex = Flex::default().size_of_parent().column();
let _expanding = button::Button::default().with_label("Expanding");
let mut normal = button::Button::default().with_label("Normal");
flex.set_size(&mut normal, 30);
flex.end();
win.end();
win.make_resizable(true);
win.show();
a.run().unwrap();
}