target ui indicating health too (#17)

src/backpack/mod.rs

@@ -5,12 +5,18 @@ use bevy::prelude::*;
 
 pub use backpack_ui::BackpackAction;
 
-#[derive(Clone, Copy, Debug)]
+#[derive(Clone, Copy, Debug, PartialEq)]
 pub struct BackpackHead {
     pub head: usize,
     pub health: f32,
 }
 
+impl BackpackHead {
+    pub fn damage(&self) -> f32 {
+        1. - self.health
+    }
+}
+
 #[derive(Resource, Default)]
 pub struct Backpack {
     pub heads: Vec<BackpackHead>,