ammo system

* heads have abilities
* health and ammo shows in ui

src/backpack/ui_head_state.rs

@@ -0,0 +1,30 @@
+use bevy::prelude::*;
+
+use crate::active_heads::HeadState;
+
+#[derive(Clone, Copy, Debug, PartialEq, Reflect, Default)]
+pub struct UiHeadState {
+    pub head: usize,
+    pub health: f32,
+    pub ammo: f32,
+}
+
+impl UiHeadState {
+    pub fn damage(&self) -> f32 {
+        1. - self.health
+    }
+
+    pub fn ammo_used(&self) -> f32 {
+        1. - self.ammo
+    }
+}
+
+impl From<HeadState> for UiHeadState {
+    fn from(value: HeadState) -> Self {
+        Self {
+            head: value.head,
+            ammo: value.ammo as f32 / value.ammo_max as f32,
+            health: value.health as f32 / value.health_max as f32,
+        }
+    }
+}