hello ecs implementation from rltk book

.gitignore

@@ -9,4 +9,3 @@ Cargo.lock
 
 # These are backup files generated by rustfmt
 **/*.rs.bk
-

Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "hellorust"
+version = "0.1.0"
+authors = ["Peter Hart <cinphart@gmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+rltk = { version = "0.7.0" }
+specs = "0.16.1"
+specs-derive = "0.4.1"

src/main.rs

@@ -0,0 +1,72 @@
+use rltk::{Console, GameState, Rltk, RGB, VirtualKeyCode};
+use specs::prelude::*;
+use std::cmp::{max, min};
+
+#[macro_use]
+extern crate specs_derive;
+
+#[derive(Component)]
+struct Position {
+    x: i32,
+    y: i32,
+}
+
+#[derive(Component)]
+struct Renderable {
+    glyph: u8,
+    fg: RGB,
+    bg: RGB,
+}
+
+struct State {
+    ecs: World
+}
+
+impl GameState for State {
+    fn tick(&mut self, ctx : &mut Rltk) {
+        ctx.cls();
+        let positions = self.ecs.read_storage::<Position>();
+        let renderables = self.ecs.read_storage::<Renderable>();
+
+        for (pos, render) in (&positions, &renderables).join() {
+            ctx.set(pos.x, pos.y, render.fg, render.bg, render.glyph);
+        }
+    }
+}
+
+fn main() {
+    use rltk::RltkBuilder;
+    let context = RltkBuilder::simple80x50()
+        .with_title("Roguelike Tutorial")
+        .build();
+    let mut gs = State {
+        ecs: World::new()
+    };
+    gs.ecs.register::<Position>();
+    gs.ecs.register::<Renderable>();
+
+    gs.ecs
+        .create_entity()
+        .with(Position { x: 40, y: 25 })
+        .with(Renderable {
+            glyph: rltk::to_cp437('@'),
+            fg: RGB::named(rltk::YELLOW),
+            bg: RGB::named(rltk::BLACK),
+        })
+        .build();
+
+    for i in 0..10 {
+        gs.ecs
+        .create_entity()
+        .with(Position { x: i * 7, y: 20 })
+        .with(Renderable {
+            glyph: rltk::to_cp437('☺'),
+            fg: RGB::named(rltk::RED),
+            bg: RGB::named(rltk::BLACK),
+        })
+        .build();
+    }
+
+    rltk::main_loop(context, gs);
+}
+