Add 3d shapes example (#4613)

# Objective

- As requested here: #4520 (comment)
- Make it easier to spot issues with built-in shapes

## Solution

https://user-images.githubusercontent.com/200550/165624709-c40dfe7e-0e1e-4bd3-ae52-8ae66888c171.mp4

- Add an example showcasing the built-in 3d shapes with lighting/shadows
- Rotate objects in such a way that all faces are seen by the camera
- Add a UV debug texture

## Discussion

I'm not sure if this is what @alice-i-cecile had in mind, but I adapted the little "torus playground" from the issue linked above to include all built-in shapes.

This exact arrangement might not be particularly scalable if many more shapes are added. Maybe a slow camera pan, or cycling with the keyboard or on a timer, or a sidebar with buttons would work better. If one of the latter options is used, options for showing wireframes or computed flat normals might add some additional utility.

Ideally, I think we'd have a better way of visualizing normals.

Happy to rework this or close it if there's not a consensus around it being useful.

Cargo.toml

@@ -200,6 +200,10 @@ path = "examples/3d/pbr.rs"
 name = "shadow_biases"
 path = "examples/3d/shadow_biases.rs"
 
+[[example]]
+name = "3d_shapes"
+path = "examples/3d/shapes.rs"
+
 [[example]]
 name = "shadow_caster_receiver"
 path = "examples/3d/shadow_caster_receiver.rs"

examples/3d/shapes.rs

@@ -0,0 +1,121 @@
+//! This example demonstrates the built-in 3d shapes in Bevy.
+//! The scene includes a patterned texture and a rotation for visualizing the normals and UVs.
+
+use bevy::{
+    prelude::*,
+    render::render_resource::{Extent3d, TextureDimension, TextureFormat},
+};
+
+fn main() {
+    App::new()
+        .insert_resource(Msaa { samples: 4 })
+        .add_plugins(DefaultPlugins)
+        .add_startup_system(setup)
+        .add_system(rotate)
+        .run();
+}
+
+/// A marker component for our shapes so we can query them separately from the ground plane
+#[derive(Component)]
+struct Shape;
+
+const X_EXTENT: f32 = 14.;
+
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut images: ResMut<Assets<Image>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    let debug_material = materials.add(StandardMaterial {
+        base_color_texture: Some(images.add(uv_debug_texture())),
+        ..default()
+    });
+
+    let shapes = [
+        meshes.add(shape::Cube::default().into()),
+        meshes.add(shape::Box::default().into()),
+        meshes.add(shape::Capsule::default().into()),
+        meshes.add(shape::Torus::default().into()),
+        meshes.add(shape::Icosphere::default().into()),
+        meshes.add(shape::UVSphere::default().into()),
+    ];
+
+    let num_shapes = shapes.len();
+
+    for (i, shape) in shapes.into_iter().enumerate() {
+        commands
+            .spawn_bundle(PbrBundle {
+                mesh: shape,
+                material: debug_material.clone(),
+                transform: Transform {
+                    translation: Vec3::new(
+                        -X_EXTENT / 2. + i as f32 / (num_shapes - 1) as f32 * X_EXTENT,
+                        2.0,
+                        0.0,
+                    ),
+                    ..default()
+                },
+                ..Default::default()
+            })
+            .insert(Shape);
+    }
+
+    commands.spawn_bundle(PointLightBundle {
+        point_light: PointLight {
+            intensity: 9000.0,
+            range: 100.,
+            shadows_enabled: true,
+            ..Default::default()
+        },
+        transform: Transform::from_xyz(8.0, 16.0, 8.0),
+        ..Default::default()
+    });
+
+    // ground plane
+    commands.spawn_bundle(PbrBundle {
+        mesh: meshes.add(shape::Plane { size: 50. }.into()),
+        material: materials.add(Color::SILVER.into()),
+        ..Default::default()
+    });
+
+    commands.spawn_bundle(PerspectiveCameraBundle {
+        transform: Transform::from_xyz(0.0, 6., 12.0).looking_at(Vec3::new(0., 1., 0.), Vec3::Y),
+        ..Default::default()
+    });
+}
+
+fn rotate(mut query: Query<&mut Transform, With<Shape>>, time: Res<Time>) {
+    for mut transform in query.iter_mut() {
+        transform.rotation = Quat::from_rotation_y(time.seconds_since_startup() as f32 / 2.)
+            * Quat::from_rotation_x(-std::f32::consts::PI / 4.)
+    }
+}
+
+/// Creates a colorful test pattern
+fn uv_debug_texture() -> Image {
+    const TEXTURE_SIZE: usize = 8;
+
+    let mut palette: [u8; 32] = [
+        255, 102, 159, 255, 255, 159, 102, 255, 236, 255, 102, 255, 121, 255, 102, 255, 102, 255,
+        198, 255, 102, 198, 255, 255, 121, 102, 255, 255, 236, 102, 255, 255,
+    ];
+
+    let mut texture_data = [0; TEXTURE_SIZE * TEXTURE_SIZE * 4];
+    for y in 0..TEXTURE_SIZE {
+        let offset = TEXTURE_SIZE * y * 4;
+        texture_data[offset..(offset + TEXTURE_SIZE * 4)].copy_from_slice(&palette);
+        palette.rotate_right(4);
+    }
+
+    Image::new_fill(
+        Extent3d {
+            width: TEXTURE_SIZE as u32,
+            height: TEXTURE_SIZE as u32,
+            depth_or_array_layers: 1,
+        },
+        TextureDimension::D2,
+        &texture_data,
+        TextureFormat::Rgba8UnormSrgb,
+    )
+}

examples/README.md

@@ -116,6 +116,7 @@ Example | File | Description
 `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
+`3d_shapes` | [`3d/shapes.rs`](./3d/shapes.rs) | A scene showcasing the built-in 3D shapes
 
 ## Animation