2 files changed, 94 insertions, 0 deletions
diff --git a/src/boid.rs b/src/boid.rs
new file mode 100644
index 0000000..dfc0755
--- /dev/null
+++ b/src/boid.rs
@@ -0,0 +1,52 @@
+use std::f32::consts::{FRAC_PI_2};
+
+use sdl2::rect::Point;
+use sdl2::render::Canvas;
+
+pub struct Boid {
+    dir_x: f32,
+    dir_y: f32,
+    position: Point,
+}
+
+const TRIANGLE_SIZE: i32 = 20;
+const SPEED: f32 = 10.0;
+
+use sdl2::video::Window;
+impl Boid {
+    pub fn new(position: Point) -> Boid {
+        Boid { dir_x: 0.1, dir_y: 0.2, position }
+    }
+
+    pub fn draw(&self, canvas: &mut Canvas<Window>) {
+        let top       = self.position.offset(0, -TRIANGLE_SIZE);
+        let bot_left  = self.position.offset(-TRIANGLE_SIZE / 3, TRIANGLE_SIZE / 2);
+        let bot_right = self.position.offset(TRIANGLE_SIZE / 3, TRIANGLE_SIZE / 2);
+
+        // direction angle = t
+        // tan t = y / x
+        // rotation
+        // | x cos t  -y sin t |
+        // | x sin t   y cos t |
+
+        let angle = (self.dir_y / self.dir_x).atan() + FRAC_PI_2;
+        let s = angle.sin();
+        let c = angle.cos();
+
+        let ps: Vec<Point> = [top, bot_left, bot_right, top].iter().map(|p| {
+            let x = (p.x() - self.position.x()) as f32;
+            let y = (p.y() - self.position.y()) as f32;
+            Point::new((x * c - y * s) as i32 + self.position.x(),
+                       (x * s + y * c) as i32 + self.position.y())
+        }).collect();
+
+        canvas.draw_lines(&ps[..]).unwrap();
+    }
+
+    pub fn step(&mut self) {
+        self.position = self.position.offset(
+            (self.dir_x * SPEED) as i32,
+            (self.dir_y * SPEED) as i32
+        );
+    }
+}
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..4c6ce8f
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,42 @@
+extern crate sdl2;
+
+use sdl2::event::Event;
+use sdl2::keyboard::Keycode;
+use sdl2::pixels::Color;
+use sdl2::rect::Point;
+
+pub mod boid;
+use boid::Boid;
+
+fn main() {
+    let sdl = sdl2::init().unwrap();
+    let video_subsys = sdl.video().unwrap();
+
+    let window = video_subsys.window("boids", 640, 480).build().unwrap();
+    let mut canvas = window.into_canvas().build().unwrap();
+
+    let mut b = Boid::new(Point::new(50, 50));
+
+    let mut event_pump = sdl.event_pump().unwrap();
+    'main: loop {
+        for event in event_pump.poll_iter() {
+            match event {
+                Event::Quit { .. } |
+                Event::KeyDown { keycode: Some(Keycode::Q), .. } |
+                Event::KeyDown { keycode: Some(Keycode::Escape), .. }
+                    => break 'main,
+                _ => {},
+            }
+        }
+        canvas.set_draw_color(Color::RGB(0, 0, 0));
+        canvas.clear();
+        canvas.set_draw_color(Color::RGB(200, 200, 200));
+        b.draw(&mut canvas);
+
+        canvas.present();
+
+        b.step();
+
+        std::thread::sleep(std::time::Duration::new(0, 50_000_000));
+    }
+}