Add tutorial for torus

Author: fogarecious

README.md

@@ -110,7 +110,7 @@ We try to keep each part of the tutorial as simple as possible.
   * [Icosphere](./tutorial/icosphere.md)
   * [Cylinder](./tutorial/cylinder.md)
   * [Capsule](./tutorial/capsule.md)
-  * Torus
+  * [Torus](./tutorial/torus.md)
   * Plane
 * Transformation
   * 3D Transformation

tutorial/capsule.md

@@ -81,6 +81,6 @@ Result:
 
 ![Capsule](./pic/capsule.png)
 
-<!-- :arrow_right:  Next:  -->
+:arrow_right:  Next: [Torus](./torus.md)
 
 :blue_book: Back: [Table of contents](./../README.md)

tutorial/pic/torus.png

@@ -0,0 +1,86 @@
+# Torus
+
+A [Torus](https://docs.rs/bevy/latest/bevy/prelude/shape/struct.Torus.html) is a donut-like shape.
+
+```rust
+commands.spawn(PbrBundle {
+    mesh: meshes
+        .add(
+            Torus {
+                radius: 0.5,
+                ring_radius: 0.1,
+                ..default()
+            }
+            .into(),
+        )
+        .into(),
+    ..default()
+});
+```
+
+We can set the [radius](https://docs.rs/bevy/latest/bevy/prelude/shape/struct.Torus.html#structfield.radius) of the [Torus](https://docs.rs/bevy/latest/bevy/prelude/shape/struct.Torus.html) and the radius ([ring_radius](https://docs.rs/bevy/latest/bevy/prelude/shape/struct.Torus.html#structfield.ring_radius)) of the [Torus](https://docs.rs/bevy/latest/bevy/prelude/shape/struct.Torus.html)'s ring.
+
+We set our camera position to `(2, 1, 3)` and make it looking at the origin.
+
+The full code is as follows:
+
+```rust
+use bevy::{
+    app::{App, Startup},
+    asset::Assets,
+    core_pipeline::core_3d::Camera3dBundle,
+    ecs::system::{Commands, ResMut},
+    math::Vec3,
+    pbr::{PbrBundle, PointLightBundle, StandardMaterial},
+    render::mesh::{shape::Torus, Mesh},
+    transform::components::Transform,
+    utils::default,
+    DefaultPlugins,
+};
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_systems(Startup, setup)
+        .run();
+}
+
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    commands.spawn(Camera3dBundle {
+        transform: Transform::from_xyz(2., 1., 3.).looking_at(Vec3::ZERO, Vec3::Y),
+        ..default()
+    });
+
+    commands.spawn(PbrBundle {
+        mesh: meshes
+            .add(
+                Torus {
+                    radius: 0.5,
+                    ring_radius: 0.1,
+                    ..default()
+                }
+                .into(),
+            )
+            .into(),
+        material: materials.add(StandardMaterial::default()).into(),
+        ..default()
+    });
+
+    commands.spawn(PointLightBundle {
+        transform: Transform::from_xyz(2., 2., 1.),
+        ..default()
+    });
+}
+```
+
+Result:
+
+![Torus](./pic/torus.png)
+
+<!-- :arrow_right:  Next:  -->
+
+:blue_book: Back: [Table of contents](./../README.md)