Switch to portable RNG in examples (#12644)

# Objective

Fixes issue #12613 - the RNG used in examples is _deterministic_, but
its implementation is not _portable_ across platforms. We want to switch
to using a portable RNG that does not vary across platforms, to ensure
certain examples play out the same way every time.

## Solution

Replace all occurences of `rand::rngs::StdRng` with
`rand_chacha::ChaCha8Rng`, as recommended in issue #12613

---

## Changelog

- Add `rand_chacha` as a new dependency (controversial?)
- Replace all occurences of `rand::rngs::StdRng` with
`rand_chacha::ChaCha8Rng`

Cargo.toml

@@ -330,6 +330,7 @@ bevy_internal = { path = "crates/bevy_internal", version = "0.14.0-dev", default
 
 [dev-dependencies]
 rand = "0.8.0"
+rand_chacha = "0.3.1"
 ron = "0.8.0"
 flate2 = "1.0"
 serde = { version = "1", features = ["derive"] }

examples/3d/spotlight.rs

@@ -7,7 +7,8 @@ use bevy::{
     pbr::NotShadowCaster,
     prelude::*,
 };
-use rand::{rngs::StdRng, Rng, SeedableRng};
+use rand::{Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
 
 const INSTRUCTIONS: &str = "\
 Controls
@@ -48,7 +49,7 @@ fn setup(
     ));
 
     // cubes
-    let mut rng = StdRng::seed_from_u64(19878367467713);
+    let mut rng = ChaCha8Rng::seed_from_u64(19878367467713);
     let cube_mesh = meshes.add(Cuboid::new(0.5, 0.5, 0.5));
     let blue = materials.add(Color::srgb_u8(124, 144, 255));
 

examples/animation/custom_skinned_mesh.rs

@@ -14,7 +14,8 @@ use bevy::{
         render_asset::RenderAssetUsages,
     },
 };
-use rand::{rngs::StdRng, Rng, SeedableRng};
+use rand::{Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
 
 fn main() {
     App::new()
@@ -122,7 +123,7 @@ fn setup(
 
     let mesh = meshes.add(mesh);
 
-    let mut rng = StdRng::seed_from_u64(42);
+    let mut rng = ChaCha8Rng::seed_from_u64(42);
 
     for i in -5..5 {
         // Create joint entities

examples/async_tasks/external_source_external_thread.rs

@@ -3,7 +3,8 @@
 use bevy::prelude::*;
 // Using crossbeam_channel instead of std as std `Receiver` is `!Sync`
 use crossbeam_channel::{bounded, Receiver};
-use rand::{rngs::StdRng, Rng, SeedableRng};
+use rand::{Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
 use std::time::{Duration, Instant};
 
 fn main() {
@@ -26,7 +27,7 @@ fn setup(mut commands: Commands) {
 
     let (tx, rx) = bounded::<u32>(10);
     std::thread::spawn(move || {
-        let mut rng = StdRng::seed_from_u64(19878367467713);
+        let mut rng = ChaCha8Rng::seed_from_u64(19878367467713);
         loop {
             // Everything here happens in another thread
             // This is where you could connect to an external data source

examples/ecs/iter_combinations.rs

@@ -1,7 +1,8 @@
 //! Shows how to iterate over combinations of query results.
 
 use bevy::{color::palettes::css::ORANGE_RED, prelude::*};
-use rand::{rngs::StdRng, Rng, SeedableRng};
+use rand::{Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
 
 fn main() {
     App::new()
@@ -44,7 +45,7 @@ fn generate_bodies(
     let color_range = 0.5..1.0;
     let vel_range = -0.5..0.5;
 
-    let mut rng = StdRng::seed_from_u64(19878367467713);
+    let mut rng = ChaCha8Rng::seed_from_u64(19878367467713);
     for _ in 0..NUM_BODIES {
         let radius: f32 = rng.gen_range(0.1..0.7);
         let mass_value = radius.powi(3) * 10.;

examples/ecs/parallel_query.rs

@@ -2,7 +2,8 @@
 
 use bevy::ecs::query::BatchingStrategy;
 use bevy::prelude::*;
-use rand::{rngs::StdRng, Rng, SeedableRng};
+use rand::{Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
 
 #[derive(Component, Deref)]
 struct Velocity(Vec2);
@@ -10,7 +11,7 @@ struct Velocity(Vec2);
 fn spawn_system(mut commands: Commands, asset_server: Res<AssetServer>) {
     commands.spawn(Camera2dBundle::default());
     let texture = asset_server.load("branding/icon.png");
-    let mut rng = StdRng::seed_from_u64(19878367467713);
+    let mut rng = ChaCha8Rng::seed_from_u64(19878367467713);
     for _ in 0..128 {
         commands.spawn((
             SpriteBundle {

examples/games/alien_cake_addict.rs

@@ -3,7 +3,8 @@
 use std::f32::consts::PI;
 
 use bevy::prelude::*;
-use rand::{rngs::StdRng, Rng, SeedableRng};
+use rand::{Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
 
 #[derive(Clone, Eq, PartialEq, Debug, Hash, Default, States)]
 enum GameState {
@@ -82,7 +83,7 @@ struct Game {
 }
 
 #[derive(Resource, Deref, DerefMut)]
-struct Random(StdRng);
+struct Random(ChaCha8Rng);
 
 const BOARD_SIZE_I: usize = 14;
 const BOARD_SIZE_J: usize = 21;
@@ -110,9 +111,9 @@ fn setup_cameras(mut commands: Commands, mut game: ResMut<Game>) {
 fn setup(mut commands: Commands, asset_server: Res<AssetServer>, mut game: ResMut<Game>) {
     let mut rng = if std::env::var("GITHUB_ACTIONS") == Ok("true".to_string()) {
         // Make the game play out the same way every time, this is useful for testing purposes.
-        StdRng::seed_from_u64(19878367467713)
+        ChaCha8Rng::seed_from_u64(19878367467713)
     } else {
-        StdRng::from_entropy()
+        ChaCha8Rng::from_entropy()
     };
 
     // reset the game state

examples/gizmos/axes.rs

@@ -1,7 +1,8 @@
 //! This example demonstrates the implementation and behavior of the axes gizmo.
 use bevy::prelude::*;
 use bevy::render::primitives::Aabb;
-use rand::{rngs::StdRng, Rng, SeedableRng};
+use rand::{Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
 use std::f32::consts::PI;
 
 const TRANSITION_DURATION: f32 = 2.0;
@@ -34,14 +35,14 @@ struct TransformTracking {
 }
 
 #[derive(Resource)]
-struct SeededRng(StdRng);
+struct SeededRng(ChaCha8Rng);
 
 fn setup(
     mut commands: Commands,
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<StandardMaterial>>,
 ) {
-    let mut rng = StdRng::seed_from_u64(19878367467713);
+    let mut rng = ChaCha8Rng::seed_from_u64(19878367467713);
 
     // Lights...
     commands.spawn(PointLightBundle {

examples/stress_tests/bevymark.rs

@@ -18,7 +18,8 @@ use bevy::{
     window::{PresentMode, WindowResolution},
     winit::{UpdateMode, WinitSettings},
 };
-use rand::{rngs::StdRng, seq::SliceRandom, Rng, SeedableRng};
+use rand::{seq::SliceRandom, Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
 
 const BIRDS_PER_SECOND: u32 = 10000;
 const GRAVITY: f32 = -9.8 * 100.0;
@@ -181,10 +182,10 @@ struct BirdResources {
     textures: Vec<Handle<Image>>,
     materials: Vec<Handle<ColorMaterial>>,
     quad: Mesh2dHandle,
-    color_rng: StdRng,
-    material_rng: StdRng,
-    velocity_rng: StdRng,
-    transform_rng: StdRng,
+    color_rng: ChaCha8Rng,
+    material_rng: ChaCha8Rng,
+    velocity_rng: ChaCha8Rng,
+    transform_rng: ChaCha8Rng,
 }
 
 #[derive(Component)]
@@ -221,10 +222,10 @@ fn setup(
         quad: meshes
             .add(Rectangle::from_size(Vec2::splat(BIRD_TEXTURE_SIZE as f32)))
             .into(),
-        color_rng: StdRng::seed_from_u64(42),
-        material_rng: StdRng::seed_from_u64(42),
-        velocity_rng: StdRng::seed_from_u64(42),
-        transform_rng: StdRng::seed_from_u64(42),
+        color_rng: ChaCha8Rng::seed_from_u64(42),
+        material_rng: ChaCha8Rng::seed_from_u64(42),
+        velocity_rng: ChaCha8Rng::seed_from_u64(42),
+        transform_rng: ChaCha8Rng::seed_from_u64(42),
     };
 
     let text_section = move |color: Srgba, value: &str| {
@@ -300,11 +301,11 @@ fn mouse_handler(
     windows: Query<&Window>,
     bird_resources: ResMut<BirdResources>,
     mut counter: ResMut<BevyCounter>,
-    mut rng: Local<Option<StdRng>>,
+    mut rng: Local<Option<ChaCha8Rng>>,
     mut wave: Local<usize>,
 ) {
     if rng.is_none() {
-        *rng = Some(StdRng::seed_from_u64(42));
+        *rng = Some(ChaCha8Rng::seed_from_u64(42));
     }
     let rng = rng.as_mut().unwrap();
     let window = windows.single();
@@ -332,7 +333,7 @@ fn mouse_handler(
 fn bird_velocity_transform(
     half_extents: Vec2,
     mut translation: Vec3,
-    velocity_rng: &mut StdRng,
+    velocity_rng: &mut ChaCha8Rng,
     waves: Option<usize>,
     dt: f32,
 ) -> (Transform, Vec3) {
@@ -537,7 +538,7 @@ fn counter_system(
 }
 
 fn init_textures(textures: &mut Vec<Handle<Image>>, args: &Args, images: &mut Assets<Image>) {
-    let mut color_rng = StdRng::seed_from_u64(42);
+    let mut color_rng = ChaCha8Rng::seed_from_u64(42);
     while textures.len() < args.material_texture_count {
         let pixel = [color_rng.gen(), color_rng.gen(), color_rng.gen(), 255];
         textures.push(images.add(Image::new_fill(
@@ -572,8 +573,8 @@ fn init_materials(
         texture: textures.first().cloned(),
     }));
 
-    let mut color_rng = StdRng::seed_from_u64(42);
-    let mut texture_rng = StdRng::seed_from_u64(42);
+    let mut color_rng = ChaCha8Rng::seed_from_u64(42);
+    let mut texture_rng = ChaCha8Rng::seed_from_u64(42);
     materials.extend(
         std::iter::repeat_with(|| {
             assets.add(ColorMaterial {

examples/stress_tests/many_cubes.rs

@@ -23,7 +23,8 @@ use bevy::{
     window::{PresentMode, WindowResolution},
     winit::{UpdateMode, WinitSettings},
 };
-use rand::{rngs::StdRng, seq::SliceRandom, Rng, SeedableRng};
+use rand::{seq::SliceRandom, Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
 
 #[derive(FromArgs, Resource)]
 /// `many_cubes` stress test
@@ -123,7 +124,7 @@ fn setup(
     let material_textures = init_textures(args, images);
     let materials = init_materials(args, &material_textures, material_assets);
 
-    let mut material_rng = StdRng::seed_from_u64(42);
+    let mut material_rng = ChaCha8Rng::seed_from_u64(42);
     match args.layout {
         Layout::Sphere => {
             // NOTE: This pattern is good for testing performance of culling as it provides roughly
@@ -202,7 +203,7 @@ fn setup(
 }
 
 fn init_textures(args: &Args, images: &mut Assets<Image>) -> Vec<Handle<Image>> {
-    let mut color_rng = StdRng::seed_from_u64(42);
+    let mut color_rng = ChaCha8Rng::seed_from_u64(42);
     let color_bytes: Vec<u8> = (0..(args.material_texture_count * 4))
         .map(|i| if (i % 4) == 3 { 255 } else { color_rng.gen() })
         .collect();
@@ -246,8 +247,8 @@ fn init_materials(
         ..default()
     }));
 
-    let mut color_rng = StdRng::seed_from_u64(42);
-    let mut texture_rng = StdRng::seed_from_u64(42);
+    let mut color_rng = ChaCha8Rng::seed_from_u64(42);
+    let mut texture_rng = ChaCha8Rng::seed_from_u64(42);
     materials.extend(
         std::iter::repeat_with(|| {
             assets.add(StandardMaterial {

examples/transforms/align.rs

@@ -6,7 +6,8 @@ use bevy::color::{
 };
 use bevy::input::mouse::{MouseButton, MouseButtonInput, MouseMotion};
 use bevy::prelude::*;
-use rand::{rngs::StdRng, Rng, SeedableRng};
+use rand::{Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
 use std::f32::consts::PI;
 
 fn main() {
@@ -44,7 +45,7 @@ struct Instructions;
 struct MousePressed(bool);
 
 #[derive(Resource)]
-struct SeededRng(StdRng);
+struct SeededRng(ChaCha8Rng);
 
 // Setup
 
@@ -53,7 +54,7 @@ fn setup(
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<StandardMaterial>>,
 ) {
-    let mut seeded_rng = StdRng::seed_from_u64(19878367467712);
+    let mut seeded_rng = ChaCha8Rng::seed_from_u64(19878367467712);
 
     // A camera looking at the origin
     commands.spawn(Camera3dBundle {

examples/ui/font_atlas_debug.rs

@@ -2,7 +2,8 @@
 //! Bevy uses `FontAtlas`'s under the hood to optimize text rendering.
 
 use bevy::{color::palettes::basic::YELLOW, prelude::*, text::FontAtlasSets};
-use rand::{rngs::StdRng, Rng, SeedableRng};
+use rand::{Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
 
 fn main() {
     App::new()
@@ -32,7 +33,7 @@ impl Default for State {
 }
 
 #[derive(Resource, Deref, DerefMut)]
-struct SeededRng(StdRng);
+struct SeededRng(ChaCha8Rng);
 
 fn atlas_render_system(
     mut commands: Commands,
@@ -104,5 +105,5 @@ fn setup(mut commands: Commands, asset_server: Res<AssetServer>, mut state: ResM
                 },
             ));
         });
-    commands.insert_resource(SeededRng(StdRng::seed_from_u64(19878367467713)));
+    commands.insert_resource(SeededRng(ChaCha8Rng::seed_from_u64(19878367467713)));
 }