First compiling version of Xairo Rust code

lib.rs

use cairo::{ImageSurface, Context, Format};
use rustler::{Env, ResourceArc, Term};
use std::fs::File;

pub struct CairoWrapper {
    pub context: Context,
    pub surface: ImageSurface
}

type WrapperRA = ResourceArc<CairoWrapper>;

#[rustler::nif]
fn new(width: i32, height: i32) -> WrapperRA {
  let surface = ImageSurface::create(Format::ARgb32, width, height).expect("Nope");
  let context = Context::new(&surface).expect("Nope");
  ResourceArc::new(
      CairoWrapper { context, surface }
  )
}

#[rustler::nif]
fn paint(context: WrapperRA, red: f64, green: f64, blue: f64) -> WrapperRA {
  context.context.set_source_rgb(red, green, blue);
  context.context.paint().unwrap();
  context
}

#[rustler::nif]
fn save(context: WrapperRA, filename: String) -> WrapperRA {
  let mut file = File::create(filename).expect("Nope");
  context.surface.write_to_png(&mut file).unwrap();
  context
}

rustler::init!("Elixir.Xairo.Native", [new, paint, save], load=on_load);

fn on_load(env: Env, _info: Term) -> bool {
    rustler::resource!(CairoWrapper, env);
    true
}