Let bullets wrap around the screen

They are now killed once having travelled the entire diagonal dimension
of the screen, which removes the last dependence on "true" x/y position.
Now, only relative position matters.

src/player.rs

@@ -196,6 +196,7 @@ impl Player {
                     pos: self.pos + self.dir * 20.,
                     vel: self.dir * 8.5 + self.vel,
                     alive: true,
+                    travelled: Vec2::new(0., 0.),
                 });
             }
         }
@@ -212,8 +213,7 @@ impl Player {
         for bullet in &mut self.bullets {
             bullet.update();
         }
-        self.bullets
+        self.bullets.retain(|b| b.alive);
-            .retain(|b| b.alive && b.pos.x.abs() * 2. < WIDTH && b.pos.y.abs() * 2. < HEIGHT);
         self.asteroids = vec![];
     }
 
@@ -277,11 +277,22 @@ struct Bullet {
     pos: Vec2,
     vel: Vec2,
     alive: bool,
+    travelled: Vec2,
 }
 
 impl Bullet {
     fn update(&mut self) {
         self.pos += self.vel;
+        if self.pos.x.abs() > WIDTH * 0.5 {
+            self.pos.x *= -1.;
+        }
+        if self.pos.y.abs() > HEIGHT * 0.5 {
+            self.pos.y *= -1.;
+        }
+        self.travelled += self.vel;
+        if self.travelled.length() >= (WIDTH * WIDTH + HEIGHT * HEIGHT).sqrt() / 2. {
+            self.alive = false;
+        }
     }
     fn draw(&self, c: Color) {
         draw_circle(self.pos.x, self.pos.y, 2., Color::new(c.r, c.g, c.b, 0.9));