Un-hardcode positions and colors in 2d_shapes example (#11867)

# Objective

We recently got some neat new 2d shapes and the shapes are no longer
centered on the screen.

The hardcoded positions and colors are a pain to deal with when a new
shape is added.

## Solution

Delete a bunch of code and position shapes evenly. Assign colors evenly
too.

## Before

<img width="1280" alt="Screenshot 2024-02-14 at 3 17 40 PM"
src="https://github.com/bevyengine/bevy/assets/200550/cc9fd9a8-4019-4907-a50e-621cb656c20a">

## After

<img width="1280" alt="Screenshot 2024-02-14 at 3 17 24 PM"
src="https://github.com/bevyengine/bevy/assets/200550/033a3f91-d3bc-4ec8-af59-42a221f8b8e7">

---------

Co-authored-by: BD103 <59022059+BD103@users.noreply.github.com>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: Joona Aalto <jondolf.dev@gmail.com>

examples/2d/2d_shapes.rs

@@ -1,6 +1,9 @@
 //! Shows how to render simple primitive shapes with a single color.
 
-use bevy::{prelude::*, sprite::MaterialMesh2dBundle};
+use bevy::{
+    prelude::*,
+    sprite::{MaterialMesh2dBundle, Mesh2dHandle},
+};
 
 fn main() {
     App::new()
@@ -9,64 +12,43 @@ fn main() {
         .run();
 }
 
+const X_EXTENT: f32 = 600.;
+
 fn setup(
     mut commands: Commands,
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<ColorMaterial>>,
 ) {
     commands.spawn(Camera2dBundle::default());
 
-    // Circle
-    commands.spawn(MaterialMesh2dBundle {
-        mesh: meshes.add(Circle { radius: 50.0 }).into(),
-        material: materials.add(Color::VIOLET),
-        transform: Transform::from_translation(Vec3::new(-275.0, 0.0, 0.0)),
-        ..default()
-    });
-
-    // Ellipse
-    commands.spawn(MaterialMesh2dBundle {
-        mesh: meshes.add(Ellipse::new(25.0, 50.0)).into(),
-        material: materials.add(Color::TURQUOISE),
-        transform: Transform::from_translation(Vec3::new(-150.0, 0.0, 0.0)),
-        ..default()
-    });
-
-    // Capsule
-    commands.spawn(MaterialMesh2dBundle {
-        mesh: meshes.add(Capsule2d::new(25.0, 50.0)).into(),
-        material: materials.add(Color::LIME_GREEN),
-        transform: Transform::from_translation(Vec3::new(-50.0, 0.0, 0.0)),
-        ..default()
-    });
-
-    // Rectangle
-    commands.spawn(MaterialMesh2dBundle {
-        mesh: meshes.add(Rectangle::new(50.0, 100.0)).into(),
-        material: materials.add(Color::YELLOW),
-        transform: Transform::from_translation(Vec3::new(50.0, 0.0, 0.0)),
-        ..default()
-    });
-
-    // Hexagon
-    commands.spawn(MaterialMesh2dBundle {
-        mesh: meshes.add(RegularPolygon::new(50.0, 6)).into(),
-        material: materials.add(Color::ORANGE),
-        transform: Transform::from_translation(Vec3::new(175.0, 0.0, 0.0)),
-        ..default()
-    });
-
-    // Triangle
-    commands.spawn(MaterialMesh2dBundle {
-        mesh: meshes
-            .add(Triangle2d::new(
-                Vec2::Y * 50.0,
-                Vec2::new(-50.0, -50.0),
-                Vec2::new(50.0, -50.0),
-            ))
-            .into(),
-        material: materials.add(Color::ORANGE_RED),
-        transform: Transform::from_translation(Vec3::new(300.0, 0.0, 0.0)),
-        ..default()
-    });
+    let shapes = [
+        Mesh2dHandle(meshes.add(Circle { radius: 50.0 })),
+        Mesh2dHandle(meshes.add(Ellipse::new(25.0, 50.0))),
+        Mesh2dHandle(meshes.add(Capsule2d::new(25.0, 50.0))),
+        Mesh2dHandle(meshes.add(Rectangle::new(50.0, 100.0))),
+        Mesh2dHandle(meshes.add(RegularPolygon::new(50.0, 6))),
+        Mesh2dHandle(meshes.add(Triangle2d::new(
+            Vec2::Y * 50.0,
+            Vec2::new(-50.0, -50.0),
+            Vec2::new(50.0, -50.0),
+        ))),
+    ];
+    let num_shapes = shapes.len();
+
+    for (i, shape) in shapes.into_iter().enumerate() {
+        // Distribute colors evenly across the rainbow.
+        let color = Color::hsl(360. * i as f32 / num_shapes as f32, 0.95, 0.7);
+
+        commands.spawn(MaterialMesh2dBundle {
+            mesh: shape,
+            material: materials.add(color),
+            transform: Transform::from_xyz(
+                // Distribute shapes from -X_EXTENT to +X_EXTENT.
+                -X_EXTENT / 2. + i as f32 / (num_shapes - 1) as f32 * X_EXTENT,
+                0.0,
+                0.0,
+            ),
+            ..default()
+        });
+    }
 }