From 939ffc70a199a560ed5bcf1ebe7c637af24866c3 Mon Sep 17 00:00:00 2001
From: Robert Garrett <robertgarrett404@gmail.com>
Date: Sat, 9 Aug 2025 15:50:54 -0500
Subject: [PATCH] Add `AngularVelocity`, begin removal of `Rotation`

The rotation component is also redundant with Bevy's transform
component.

This new component and system fill the physics role, but the input
handling code needs to be updated.

Player steering still functions because it uses the `Rotation` component
to direct the force vector. The force is correctly applied to the linear
velocity vector. An improvement would be to have a force/impulse
accumulator so I could account for mass, but I'm not going to do that
right now.
---
 src/lib.rs     |  5 ++++-
 src/physics.rs | 15 +++++++++------
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 60c547e..4415e96 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -61,7 +61,10 @@ impl Plugin for AsteroidPlugin {
         )
         .add_systems(
             FixedPostUpdate,
-            (physics::integrate_velocity, physics::apply_rotation_to_mesh)
+            (
+                physics::integrate_velocity,
+                physics::integrate_angular_velocity,
+            )
                 .run_if(in_state(GameState::Playing)),
         )
         .add_event::<asteroids::SpawnAsteroid>()
diff --git a/src/physics.rs b/src/physics.rs
index 503ce87..d41fd75 100644
--- a/src/physics.rs
+++ b/src/physics.rs
@@ -26,12 +26,15 @@ pub(crate) fn integrate_velocity(mut query: Query<(&mut Transform, &Velocity)>,
     }
 }
 
-/*
- Assigns the rotation to the transform by copying it from the Rotation component.
-*/
-pub(crate) fn apply_rotation_to_mesh(mut query: Query<(&mut Transform, &Rotation)>) {
-    for (mut transform, rotation) in &mut query {
-        transform.rotation = Quat::from_rotation_z(rotation.0);
+/// Integrate angular velocity and update the entity's transform.
+pub(crate) fn integrate_angular_velocity(
+    mut objects: Query<(&mut Transform, &AngularVelocity)>,
+    time: Res<Time>,
+) {
+    for (mut transform, ang_vel) in &mut objects {
+        let delta = ang_vel.0 * time.delta_secs();
+        let temp = transform.rotation + Quat::from_rotation_z(delta);
+        transform.rotation = temp;
     }
 }