Add Animated Material example (#11524)

# Objective

- Fixes #11516

## Solution

- Add Animated Material example (colors are hue-cycling smoothly
per-mesh)


![image](https://github.com/bevyengine/bevy/assets/11307157/c75b9e66-0019-41b8-85ec-647559c6ba01)

Note: this example reproduces the perf issue found in #10610 pretty
consistently, with and without the changes from that PR included. Frame
time is sometimes around 4.3ms, other times around 12-14ms. Its pretty
random per run. I think this clears #10610 for merge.

Cargo.toml

@@ -552,6 +552,17 @@ description = "Demonstrates how to use the `Camera::viewport_to_world` method"
 category = "3D Rendering"
 wasm = true
 
+[[example]]
+name = "animated_material"
+path = "examples/3d/animated_material.rs"
+doc-scrape-examples = true
+
+[package.metadata.example.animated_material]
+name = "Animated Material"
+description = "Shows how to animate material properties"
+category = "3D Rendering"
+wasm = true
+
 [[example]]
 name = "generate_custom_mesh"
 path = "examples/3d/generate_custom_mesh.rs"

examples/3d/animated_material.rs

@@ -0,0 +1,78 @@
+//! Shows how to animate material properties
+
+use bevy::prelude::*;
+use bevy::utils::HashSet;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_systems(Startup, setup)
+        .add_systems(Update, (animate_materials, make_materials_unique))
+        .run();
+}
+
+fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
+    commands.spawn((
+        Camera3dBundle {
+            transform: Transform::from_xyz(3.0, 1.0, 3.0)
+                .looking_at(Vec3::new(0.0, -0.5, 0.0), Vec3::Y),
+            ..default()
+        },
+        EnvironmentMapLight {
+            diffuse_map: asset_server.load("environment_maps/pisa_diffuse_rgb9e5_zstd.ktx2"),
+            specular_map: asset_server.load("environment_maps/pisa_specular_rgb9e5_zstd.ktx2"),
+            intensity: 1500.0,
+        },
+    ));
+
+    let helmet = asset_server.load("models/FlightHelmet/FlightHelmet.gltf#Scene0");
+    for x in -2..3 {
+        for z in -2..3 {
+            commands.spawn(SceneBundle {
+                scene: helmet.clone(),
+                transform: Transform::from_translation(Vec3::new(x as f32, 0.0, z as f32)),
+                ..default()
+            });
+        }
+    }
+}
+
+fn animate_materials(
+    material_handles: Query<&Handle<StandardMaterial>>,
+    time: Res<Time>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    for (i, material_handle) in material_handles.iter().enumerate() {
+        if let Some(material) = materials.get_mut(material_handle) {
+            let color = Color::hsl(
+                ((i as f32 * 2.345 + time.elapsed_seconds_wrapped()) * 100.0) % 360.0,
+                1.0,
+                0.5,
+            );
+            material.base_color = color;
+            material.emissive = color;
+        }
+    }
+}
+
+/// This is needed because by default assets are loaded with shared materials
+/// But we want to animate every helmet independently of the others, so we must duplicate the materials
+fn make_materials_unique(
+    mut material_handles: Query<&mut Handle<StandardMaterial>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+    mut ran: Local<bool>,
+) {
+    if *ran {
+        return;
+    }
+    let mut set = HashSet::new();
+    for mut material_handle in material_handles.iter_mut() {
+        if set.contains(&material_handle.id()) {
+            let material = materials.get(&*material_handle).unwrap().clone();
+            *material_handle = materials.add(material);
+        } else {
+            set.insert(material_handle.id());
+        }
+        *ran = true;
+    }
+}

examples/README.md

@@ -121,6 +121,7 @@ Example | Description
 [3D Scene](../examples/3d/3d_scene.rs) | Simple 3D scene with basic shapes and lighting
 [3D Shapes](../examples/3d/3d_shapes.rs) | A scene showcasing the built-in 3D shapes
 [3D Viewport To World](../examples/3d/3d_viewport_to_world.rs) | Demonstrates how to use the `Camera::viewport_to_world` method
+[Animated Material](../examples/3d/animated_material.rs) | Shows how to animate material properties
 [Anti-aliasing](../examples/3d/anti_aliasing.rs) | Compares different anti-aliasing methods
 [Atmospheric Fog](../examples/3d/atmospheric_fog.rs) | A scene showcasing the atmospheric fog effect
 [Blend Modes](../examples/3d/blend_modes.rs) | Showcases different blend modes