trail gradient

src/abilities/missile.rs

@@ -136,7 +136,11 @@ fn on_trigger_missile(
                 SceneRoot(asset.scenes[0].clone()),
             ),
             (
-                Trail::new(t.translation, LinearRgba::rgb(0.9, 0.9, 0.)),
+                Trail::new(
+                    t.translation,
+                    LinearRgba::rgb(1., 0.0, 0.),
+                    LinearRgba::rgb(0.9, 0.9, 0.)
+                ),
                 Gizmo {
                     handle: gizmo_assets.add(GizmoAsset::default()),
                     line_config: GizmoLineConfig {

src/utils/trail.rs

@@ -5,14 +5,19 @@ use crate::GameState;
 #[derive(Component)]
 pub struct Trail {
     points: Vec<Vec3>,
-    col: LinearRgba,
+    col_start: LinearRgba,
+    col_end: LinearRgba,
 }
 
 impl Trail {
-    pub fn new(pos: Vec3, col: LinearRgba) -> Self {
+    pub fn new(pos: Vec3, col_start: LinearRgba, col_end: LinearRgba) -> Self {
         let mut v = Vec::with_capacity(12);
         v.push(pos);
-        Self { points: v, col }
+        Self {
+            points: v,
+            col_start,
+            col_end,
+        }
     }
 
     pub fn add(&mut self, pos: Vec3) {
@@ -44,7 +49,8 @@ fn update_trail(
             continue;
         };
 
-        for window in trail.points.windows(2) {
+        let lerp_denom = trail.points.len() as f32;
+        for (i, window) in trail.points.windows(2).enumerate() {
             let [a, b] = window else {
                 continue;
             };
@@ -55,7 +61,11 @@ fn update_trail(
                 .reparented_to(parent_transform)
                 .translation;
 
-            gizmo.line(a, b, trail.col);
+            gizmo.line(
+                a,
+                b,
+                trail.col_start.mix(&trail.col_end, i as f32 / lerp_denom),
+            );
         }
     }