termcandy

termcandy is a library for writing terminal user interfaces using imperative-style code. This means you don't have to structure your program around an event loop, just write code that flows naturally and let macro magic do the rest.

Example

This program will draw a blue ball bouncing around the screen until the user presses escape.

#![type_length_limit="30000000"]
#![feature(proc_macro_hygiene)]
#![feature(never_type)]
#![feature(generators)]
#![feature(label_break_value)]

use std::time::Duration;
use termcandy::{widget, select_widget};
use termcandy::input::{self, Key};
use termcandy::graphics::{Style, Color, Attrs};
use tokio::time::{self, Instant};

#[widget]
fn bouncing_ball() {
    let mut pos_x = 0;
    let mut pos_y = 0;
    let mut vel_x = 1;
    let mut vel_y = 1;
    let mut next_instant = Instant::now();
    let style = Style { fg: Color::blue(), bg: Color::default(), attrs: Attrs::bold() };
    loop {
        select_widget! {
            () = time::sleep_until(next_instant) => {
                next_instant += Duration::from_millis(200);
                let (w, h) = termcandy::screen_size();
                if pos_x <= 0 { vel_x = 1 };
                if pos_x >= w as i16 { vel_x = -1 };
                if pos_y <= 0 { vel_y = 1 };
                if pos_y >= h as i16 { vel_y = -1 };
                pos_x += vel_x;
                pos_y += vel_y;
            },
            () = input::key(Key::Esc) => return,
            never = widget::draw(|surface| {
                surface.print("●", pos_x, pos_y, style)
            }) => never,
        }
    }
}

#[tokio::main]
async fn main() {
    termcandy::run(four_bouncing_balls()).await.unwrap();
}

We could also divide the screen into 4 corners and reuse the above code to make 4 balls bounce around those corners. Note that this function doesn't require any loops to write. If you resize the terminal window while it's running it will react accordingly.

use termcandy::Widget;
use termcandy::graphics::Rect;

#[widget]
fn four_bouncing_balls() {
    let top_left = bouncing_ball().resize(|w, h| {
        Rect { x0: 0, x1: w as i16 / 2, y0: 0, y1: h as i16 / 2 }
    });
    let top_right = bouncing_ball().resize(|w, h| {
        Rect { x0: w as i16 / 2, x1: w as i16, y0: 0, y1: h as i16 / 2 }
    });
    let bottom_left = bouncing_ball().resize(|w, h| {
        Rect { x0: 0, x1: w as i16 / 2, y0: h as i16 / 2, y1: h as i16 }
    });
    let bottom_right = bouncing_ball().resize(|w, h| {
        Rect { x0: w as i16 / 2, x1: w as i16, y0: h as i16 / 2, y1: h as i16 }
    });
    select_widget! {
        () = top_left => (),
        () = top_right => (),
        () = bottom_left => (),
        () = bottom_right => (),
        never = widget::draw(|surface| {
            surface.draw_v_line(0, surface.height() as i16 - 1, 0);
            surface.draw_v_line(0, surface.height() as i16 - 1, surface.width() as i16 / 2);
            surface.draw_v_line(0, surface.height() as i16 - 1, surface.width() as i16 - 1);
            surface.draw_h_line(0, surface.width() as i16 - 1, 0);
            surface.draw_h_line(0, surface.width() as i16 - 1, surface.height() as i16 / 2);
            surface.draw_h_line(0, surface.width() as i16 - 1, surface.height() as i16 - 1);
        }) => never
    }
}