Spherical area lights example (#3498)

I was putting together the Bevy 0.6 release blog post and wanted a simple area light radius example, so here we are :)

![image](https://user-images.githubusercontent.com/2694663/147786883-63454290-b5b1-4456-9762-0b0b47e16bb5.png)

Cargo.toml

@@ -181,6 +181,10 @@ path = "examples/3d/shadow_biases.rs"
 name = "shadow_caster_receiver"
 path = "examples/3d/shadow_caster_receiver.rs"
 
+[[example]]
+name = "spherical_area_lights"
+path = "examples/3d/spherical_area_lights.rs"
+
 [[example]]
 name = "texture"
 path = "examples/3d/texture.rs"

examples/3d/spherical_area_lights.rs

@@ -0,0 +1,73 @@
+use bevy::prelude::*;
+
+fn main() {
+    App::new()
+        .insert_resource(ClearColor(Color::BLACK))
+        .add_plugins(DefaultPlugins)
+        .add_startup_system(setup)
+        .run();
+}
+
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    // camera
+    commands.spawn_bundle(PerspectiveCameraBundle {
+        transform: Transform::from_xyz(1.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
+        ..Default::default()
+    });
+
+    // plane
+    commands.spawn_bundle(PbrBundle {
+        mesh: meshes.add(Mesh::from(shape::Plane { size: 100.0 })),
+        material: materials.add(StandardMaterial {
+            base_color: Color::rgb(0.2, 0.2, 0.2),
+            perceptual_roughness: 0.08,
+            ..Default::default()
+        }),
+        ..Default::default()
+    });
+
+    const COUNT: usize = 6;
+    let position_range = -4.0..4.0;
+    let radius_range = 0.0..0.8;
+    let pos_len = position_range.end - position_range.start;
+    let radius_len = radius_range.end - radius_range.start;
+    let mesh = meshes.add(Mesh::from(shape::UVSphere {
+        sectors: 128,
+        stacks: 64,
+        ..Default::default()
+    }));
+
+    for i in 0..COUNT {
+        let percent = i as f32 / COUNT as f32;
+        let radius = radius_range.start + percent * radius_len;
+
+        // sphere light
+        commands
+            .spawn_bundle(PbrBundle {
+                mesh: mesh.clone(),
+                material: materials.add(StandardMaterial {
+                    base_color: Color::rgb(0.5, 0.5, 1.0),
+                    unlit: true,
+                    ..Default::default()
+                }),
+                transform: Transform::from_xyz(position_range.start + percent * pos_len, 0.6, 0.0)
+                    .with_scale(Vec3::splat(radius)),
+                ..Default::default()
+            })
+            .with_children(|children| {
+                children.spawn_bundle(PointLightBundle {
+                    point_light: PointLight {
+                        intensity: 1500.0,
+                        radius,
+                        color: Color::rgb(0.2, 0.2, 1.0),
+                        ..Default::default()
+                    },
+                    ..Default::default()
+                });
+            });
+    }
+}

examples/README.md

@@ -105,6 +105,7 @@ Example | File | Description
 `pbr` | [`3d/pbr.rs`](./3d/pbr.rs) | Demonstrates use of Physically Based Rendering (PBR) properties
 `shadow_caster_receiver` | [`3d/shadow_caster_receiver.rs`](./3d/shadow_caster_receiver.rs) | Demonstrates how to prevent meshes from casting/receiving shadows in a 3d scene
 `shadow_biases` | [`3d/shadow_biases.rs`](./3d/shadow_biases.rs) | Demonstrates how shadow biases affect shadows in a 3d scene
+`spherical_area_lights` | [`3d/spherical_area_lights.rs`](./3d/spherical_area_lights.rs) | Demonstrates how point light radius values affect light behavior.
 `texture` | [`3d/texture.rs`](./3d/texture.rs) | Shows configuration of texture materials
 `update_gltf_scene` | [`3d/update_gltf_scene.rs`](./3d/update_gltf_scene.rs) | Update a scene from a gltf file, either by spawning the scene as a child of another entity, or by accessing the entities of the scene
 `wireframe` | [`3d/wireframe.rs`](./3d/wireframe.rs) | Showcases wireframe rendering