From 61c57783f13e755e0aa55f3c554fcfb7373d4ed0 Mon Sep 17 00:00:00 2001
From: Robert Garrett <robertgarrett404@gmail.com>
Date: Sat, 9 Aug 2025 13:31:59 -0500
Subject: [PATCH] Split physics parts into a submodule

The physics sim bits (that aren't Rapier2d) are now in their own
submodule. I've included the `Wrapping` marker component because it
doesn't really have anywhere else to live, and it's kinda sorta related
to the physics. It controls the motion of objects... that's physics. :p

There are name collisions between Rapier2d's `Velocity` and my own, but
that's a problem for later. I've used more specific type paths where
necessary to maintain the previous behavior.

The `physics::Position` component can go away completely. It's just an
extra copy of some of the built-in `Transform` data. I'm pretty sure it
only exists because I didn't realize I could rely on directly
manipulating the transform when I started this project.
---
 src/asteroids.rs |  2 +-
 src/lib.rs       | 75 ++++++------------------------------------------
 src/physics.rs   | 72 ++++++++++++++++++++++++++++++++++++++++++++++
 src/ship.rs      |  2 +-
 4 files changed, 83 insertions(+), 68 deletions(-)
 create mode 100644 src/physics.rs

diff --git a/src/asteroids.rs b/src/asteroids.rs
index 148d6f0..f37d909 100644
--- a/src/asteroids.rs
+++ b/src/asteroids.rs
@@ -6,7 +6,7 @@ use std::time::Duration;
 /// not... not the whole game.
 use bevy::prelude::*;
 
-use crate::{GameAssets, Position, Rotation, Velocity, WorldSize};
+use crate::{GameAssets, Rotation, WorldSize, physics::Position, physics::Velocity};
 
 #[derive(Component, Deref, DerefMut)]
 pub struct Asteroid(AsteroidSize);
diff --git a/src/lib.rs b/src/lib.rs
index 5f51fed..584af16 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,6 +1,7 @@
 mod asteroids;
 pub mod config;
 mod event;
+mod physics;
 mod preparation_widget;
 mod ship;
 mod title_screen;
@@ -18,6 +19,7 @@ use bevy_rapier2d::{
     render::RapierDebugRenderPlugin,
 };
 use config::{ASTEROID_SMALL_COLOR, SHIP_THRUSTER_COLOR_ACTIVE, SHIP_THRUSTER_COLOR_INACTIVE};
+use physics::Rotation;
 use ship::Ship;
 
 pub struct AsteroidPlugin;
@@ -47,7 +49,7 @@ impl Plugin for AsteroidPlugin {
             (
                 input_ship_thruster,
                 input_ship_rotation,
-                wrap_entities,
+                physics::wrap_entities,
                 asteroids::tick_asteroid_manager,
                 asteroids::spawn_asteroid.after(asteroids::tick_asteroid_manager),
                 collision_listener,
@@ -58,7 +60,11 @@ impl Plugin for AsteroidPlugin {
         )
         .add_systems(
             FixedPostUpdate,
-            (integrate_velocity, update_positions, apply_rotation_to_mesh)
+            (
+                physics::integrate_velocity,
+                physics::update_positions,
+                physics::apply_rotation_to_mesh,
+            )
                 .run_if(in_state(GameState::Playing)),
         )
         .add_event::<asteroids::SpawnAsteroid>()
@@ -130,19 +136,6 @@ pub enum GameState {
     GameOver,    // Game has ended. Present game over dialogue and await user restart
 }
 
-#[derive(Component)]
-struct Position(bevy::math::Vec2);
-
-#[derive(Component)]
-struct Velocity(bevy::math::Vec2);
-
-#[derive(Component)]
-struct Rotation(f32);
-
-/// Marker for any entity that should wrap on screen edges
-#[derive(Component)]
-struct Wrapping;
-
 #[derive(Resource, Debug, Deref, Clone, Copy)]
 struct Score(i32);
 
@@ -244,7 +237,7 @@ fn spawn_camera(mut commands: Commands) {
 */
 fn input_ship_thruster(
     keyboard_input: Res<ButtonInput<KeyCode>>,
-    mut query: Query<(&mut Velocity, &Rotation, &mut Children), With<Ship>>,
+    mut query: Query<(&mut physics::Velocity, &Rotation, &mut Children), With<Ship>>,
     mut commands: Commands,
     game_assets: Res<GameAssets>,
 ) {
@@ -292,56 +285,6 @@ fn input_ship_rotation(
     }
 }
 
-// TODO: Combine movement integration steps into one function
-// They need to be ordered so the physics is deterministic. Bevy can enforce
-// order, but it makes more sense to cut out the extra machinery and have one
-// single function. Probably better for cache locality or whatever, too.
-/*
- Add velocity to position
-*/
-fn integrate_velocity(mut query: Query<(&mut Position, &Velocity)>, time: Res<Time>) {
-    for (mut position, velocity) in &mut query {
-        position.0 += velocity.0 * time.delta_secs();
-    }
-}
-
-fn update_positions(mut query: Query<(&mut Transform, &Position)>) {
-    for (mut transform, position) in &mut query {
-        transform.translation.x = position.0.x;
-        transform.translation.y = position.0.y;
-    }
-}
-
-/*
- Assigns the rotation to the transform by copying it from the Rotation component.
-*/
-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);
-    }
-}
-
-fn wrap_entities(mut query: Query<&mut Position, With<Wrapping>>, world_size: Res<WorldSize>) {
-    let right = world_size.width / 2.0;
-    let left = -right;
-    let top = world_size.height / 2.0;
-    let bottom = -top;
-
-    for mut pos in query.iter_mut() {
-        if pos.0.x > right {
-            pos.0.x = left;
-        } else if pos.0.x < left {
-            pos.0.x = right;
-        }
-
-        if pos.0.y > top {
-            pos.0.y = bottom;
-        } else if pos.0.y < bottom {
-            pos.0.y = top;
-        }
-    }
-}
-
 fn spawn_ui(mut commands: Commands, score: Res<Score>, lives: Res<Lives>) {
     commands.spawn((
         Text::new(format!("Score: {score:?} | Lives: {lives:?}")),
diff --git a/src/physics.rs b/src/physics.rs
new file mode 100644
index 0000000..349ce42
--- /dev/null
+++ b/src/physics.rs
@@ -0,0 +1,72 @@
+//! Custom physics items
+//! TODO: Refactor in terms of Rapier2D, *or* implement colliders and remove it.
+
+use bevy::prelude::*;
+
+use crate::WorldSize;
+
+#[derive(Component)]
+pub(crate) struct Position(pub(crate) bevy::math::Vec2);
+
+#[derive(Component)]
+pub(crate) struct Velocity(pub(crate) bevy::math::Vec2);
+
+#[derive(Component)]
+pub(crate) struct Rotation(pub(crate) f32);
+
+/// Marker for any entity that should wrap on screen edges
+#[derive(Component)]
+pub(crate) struct Wrapping;
+
+// TODO: Combine movement integration steps into one function
+// They need to be ordered so the physics is deterministic. Bevy can enforce
+// order, but it makes more sense to cut out the extra machinery and have one
+// single function. Probably better for cache locality or whatever, too.
+/*
+ Add velocity to position
+*/
+pub(crate) fn integrate_velocity(mut query: Query<(&mut Position, &Velocity)>, time: Res<Time>) {
+    for (mut position, velocity) in &mut query {
+        position.0 += velocity.0 * time.delta_secs();
+    }
+}
+
+pub(crate) fn update_positions(mut query: Query<(&mut Transform, &Position)>) {
+    for (mut transform, position) in &mut query {
+        transform.translation.x = position.0.x;
+        transform.translation.y = position.0.y;
+    }
+}
+
+/*
+ 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);
+    }
+}
+
+pub(crate) fn wrap_entities(
+    mut query: Query<&mut Position, With<Wrapping>>,
+    world_size: Res<WorldSize>,
+) {
+    let right = world_size.width / 2.0;
+    let left = -right;
+    let top = world_size.height / 2.0;
+    let bottom = -top;
+
+    for mut pos in query.iter_mut() {
+        if pos.0.x > right {
+            pos.0.x = left;
+        } else if pos.0.x < left {
+            pos.0.x = right;
+        }
+
+        if pos.0.y > top {
+            pos.0.y = bottom;
+        } else if pos.0.y < bottom {
+            pos.0.y = top;
+        }
+    }
+}
diff --git a/src/ship.rs b/src/ship.rs
index 09131bb..ed813b2 100644
--- a/src/ship.rs
+++ b/src/ship.rs
@@ -1,7 +1,7 @@
 use bevy::prelude::*;
 use bevy_rapier2d::prelude::*;
 
-use crate::{GameAssets, Position, Rotation, Velocity, Wrapping};
+use crate::{GameAssets, Rotation, physics::Position, physics::Velocity, physics::Wrapping};
 
 #[derive(Component)]
 pub struct Ship;