Rework the example slightly

Co-authored-by: Rob Parrett <robparrett@gmail.com>

examples/3d/3d_viewport_to_world.rs

@@ -1,96 +1,67 @@
 //! This example demonstrates how to use the `Camera::viewport_to_world` method.
 
-use bevy::{pbr::CascadeShadowConfigBuilder, prelude::*};
+use bevy::prelude::*;
 
 fn main() {
     App::new()
         .add_plugins(DefaultPlugins)
-        .add_startup_system(setup)
-        .add_system(move_cube)
+        .add_systems(Startup, setup)
+        .add_systems(Update, move_cube)
         .run();
 }
 
 fn move_cube(
     camera_query: Query<(&Camera, &GlobalTransform)>,
-    mut cube_query: Query<&mut Transform, With<Cube>>,
+    ground_query: Query<&Transform, With<Ground>>,
     windows: Query<&Window>,
-    input: Res<Input<MouseButton>>,
+    mut gizmos: Gizmos,
 ) {
     let (camera, camera_transform) = camera_query.single();
-    let mut transform = cube_query.single_mut();
-
-    if !input.pressed(MouseButton::Left) {
-        return;
-    }
+    let ground = ground_query.single();
 
     let Some(cursor_position) = windows.single().cursor_position() else { return; };
 
+    // Calculate a ray pointing from the camera into the world based on the cursor's position.
     let Some(ray) = camera.viewport_to_world(camera_transform, cursor_position) else { return; };
 
-    let Some(distance) = ray.intersect_plane(Vec3::ZERO, Vec3::Y) else { return; };
-
+    // Calculate if and where the ray is hitting the ground plane.
+    let Some(distance) = ray.intersect_plane(ground.translation, ground.up()) else { return; };
     let point = ray.get_point(distance);
-    transform.translation = point + Vec3::Y * 0.5;
+
+    // Draw a line poking out of the ground plane at that position.
+    gizmos.ray(point, ground.up(), Color::BLACK);
 }
 
 #[derive(Component)]
-struct Cube;
+struct Ground;
 
 fn setup(
     mut commands: Commands,
     mut meshes: ResMut<Assets<Mesh>>,
     mut materials: ResMut<Assets<StandardMaterial>>,
-    asset_server: Res<AssetServer>,
 ) {
     // plane
-    commands.spawn(PbrBundle {
-        mesh: meshes.add(Mesh::from(shape::Plane {
-            size: 50.0,
-            subdivisions: 0,
-        })),
-        material: materials.add(Color::rgb(0.3, 0.5, 0.3).into()),
-        ..default()
-    });
-
-    // cube
     commands.spawn((
         PbrBundle {
-            mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
-            material: materials.add(Color::rgb(0.8, 0.7, 0.6).into()),
-            transform: Transform::from_xyz(0.0, 0.5, 0.0),
+            mesh: meshes.add(Mesh::from(shape::Plane {
+                size: 20.0,
+                subdivisions: 0,
+            })),
+            material: materials.add(Color::rgb(0.3, 0.5, 0.3).into()),
             ..default()
         },
-        Cube,
+        Ground,
     ));
 
     // light
     commands.spawn(DirectionalLightBundle {
         transform: Transform::from_translation(Vec3::ONE).looking_at(Vec3::ZERO, Vec3::Y),
-        directional_light: DirectionalLight {
-            shadows_enabled: true,
-            ..default()
-        },
-        cascade_shadow_config: CascadeShadowConfigBuilder {
-            maximum_distance: 15.,
-            ..default()
-        }
-        .into(),
         ..default()
     });
 
     // camera
     commands.spawn(Camera3dBundle {
-        transform: Transform::from_xyz(0.0, 6.0, 6.0).looking_at(Vec3::ZERO, Vec3::Y),
+        transform: Transform::from_xyz(15.0, 5.0, 15.0).looking_at(Vec3::ZERO, Vec3::Y),
         ..default()
     });
-
-    // UI
-    commands.spawn(TextBundle::from_section(
-        "Press the left mouse button to reposition the box.",
-        TextStyle {
-            font: asset_server.load("fonts/FiraMono-Medium.ttf"),
-            font_size: 32.,
-            ..default()
-        },
-    ));
 }