Code shared from the Rust Playground

playground.rs

/// Colors are stored in RGBA format
/// The first byte is R, the second byte is G, etc.
#[derive(Debug)]
struct Color(u32);

#[derive(Debug)]
struct RelDimen {
    x:i16, y:i16, w:i16, h:i16
}

impl RelDimen {
    fn abs(&self) -> AbsDimen {
        AbsDimen {
            x: self.x.abs() as u16,
            y: self.y.abs() as u16,
            w: self.w.abs() as u16,
            h: self.h.abs() as u16,
        }
    }
}

#[derive(Debug)]
struct AbsDimen {
    x:u16, y:u16, w:u16, h:u16
}

#[derive(Debug)]
enum Message {
    Rect{dimen:AbsDimen, fill:Color},
    Text{dimen:AbsDimen, fill:Color, fg:Color},
}

type MessageList = Vec<Message>;

trait Widget {
    fn draw(&self) -> MessageList;
    fn window(&self) -> Option<&Window>;
}

struct Box {
    dimen: RelDimen,
}

impl Box {
    fn new(x: i16, y:i16, w:i16, h:i16) -> Box {
        return Box{dimen: RelDimen{x:x, y:y, w:w, h:h}};
    }
}

impl Widget for Box {
    fn draw(&self) -> MessageList {
        vec![Message::Rect{dimen:self.dimen.abs(), fill:Color(0)}]
    }
    
    fn window(&self) -> Option<&Window> {
        None
    }
}

struct Window {
    dimen: AbsDimen,
}

fn main() {
    let b = Box::new(0,0,50,50);
    println!("{:?}",b.draw());
}