From 20eb13f4588245550937611f72fb5e608fd27178 Mon Sep 17 00:00:00 2001
From: Chris Biscardi <chris@christopherbiscardi.com>
Date: Tue, 18 Jun 2024 04:38:17 -0700
Subject: [PATCH] Use smooth_nudge in 2d_top_down_camera example (#13907)
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# Objective


[`StableInterpolate`](https://dev-docs.bevyengine.org/bevy/math/trait.StableInterpolate.html)
was introduced after this example was written (or more accurately, the
two PRs were merged on the same day and developed in parallel).

The example used `Vec3::lerp` where I believe it is now preferred to use
`smooth_nudge`.

## Solution

Its not entirely clear to me whether `StableInterpolate` should be
preferred in this scenario, although it seems likely. So I figured a PR
to make the change would either result in it being merged or denied with
a reason.

## Testing

```
cargo run --example 2d_top_down_camera
```

Co-authored-by: François Mockers <mockersf@gmail.com>
---
 examples/camera/2d_top_down_camera.rs | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/examples/camera/2d_top_down_camera.rs b/examples/camera/2d_top_down_camera.rs
index 7321712988d62..ad565b36f54bd 100644
--- a/examples/camera/2d_top_down_camera.rs
+++ b/examples/camera/2d_top_down_camera.rs
@@ -17,8 +17,8 @@ use bevy::sprite::{MaterialMesh2dBundle, Mesh2dHandle};
 /// Player movement speed factor.
 const PLAYER_SPEED: f32 = 100.;
 
-/// Camera lerp factor.
-const CAM_LERP_FACTOR: f32 = 2.;
+/// How quickly should the camera snap to the desired location.
+const CAMERA_DECAY_RATE: f32 = 2.;
 
 #[derive(Component)]
 struct Player;
@@ -103,14 +103,11 @@ fn update_camera(
     let Vec3 { x, y, .. } = player.translation;
     let direction = Vec3::new(x, y, camera.translation.z);
 
-    // Applies a smooth effect to camera movement using interpolation between
-    // the camera position and the player position on the x and y axes.
-    // Here we use the in-game time, to get the elapsed time (in seconds)
-    // since the previous update. This avoids jittery movement when tracking
-    // the player.
-    camera.translation = camera
+    // Applies a smooth effect to camera movement using stable interpolation
+    // between the camera position and the player position on the x and y axes.
+    camera
         .translation
-        .lerp(direction, time.delta_seconds() * CAM_LERP_FACTOR);
+        .smooth_nudge(&direction, CAMERA_DECAY_RATE, time.delta_seconds());
 }
 
 /// Update the player position with keyboard inputs.