feat: smooth back-forth sprite frame ticks, sprite rotation

src/direction.rs

@@ -1,6 +1,18 @@
+#[derive(Debug, Copy, Clone, PartialEq)]
 pub enum Direction {
     Up,
     Down,
     Left,
     Right,
+}
+
+impl Direction {
+    pub fn angle(&self) -> f64 {
+        match self {
+            Direction::Right => 0f64,
+            Direction::Down => 90f64,
+            Direction::Left => 180f64,
+            Direction::Up => 270f64,
+        }
+    }
 }