Refactor cursor grabbing and more

- Rename `free_camera` to `camera`
- Move cursor grabbing logic to its own system
- (Hopefully) improve readability
- Move cursor to window center on grab
- Reorganize system scheduling
- Use `.after` and `.run_if`

src/block.rs

@@ -0,0 +1,39 @@
+use bevy::ecs::system::SystemParam;
+use bevy::prelude::*;
+
+#[derive(Component)]
+pub struct Block;
+
+#[derive(SystemParam)]
+pub struct Blocks<'w, 's> {
+    commands: Commands<'w, 's>,
+    block_resources: Res<'w, BlockResources>,
+}
+
+impl Blocks<'_, '_> {
+    pub fn spawn(&mut self, pos: IVec3) {
+        self.commands.spawn((
+            Block,
+            Mesh3d(self.block_resources.mesh.clone()),
+            MeshMaterial3d(self.block_resources.material.clone()),
+            Transform::from_translation(pos.as_vec3() + Vec3::ONE / 2.),
+        ));
+    }
+}
+
+#[derive(Resource)]
+pub struct BlockResources {
+    mesh: Handle<Mesh>,
+    material: Handle<StandardMaterial>,
+}
+
+pub fn setup_blocks(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    commands.insert_resource(BlockResources {
+        mesh: meshes.add(Cuboid::new(1.0, 1.0, 1.0)),
+        material: materials.add(Color::srgb_u8(124, 144, 255)),
+    });
+}

src/camera.rs

@@ -4,6 +4,53 @@ use bevy::input::mouse::AccumulatedMouseMotion;
 use bevy::prelude::*;
 use bevy::window::{CursorGrabMode, CursorOptions};
 
+pub fn cursor_grab(
+    mut mouse_button_input: ResMut<ButtonInput<MouseButton>>,
+    key_input: Res<ButtonInput<KeyCode>>,
+    window: Single<(&mut Window, &mut CursorOptions)>,
+    crosshair: Single<&mut Visibility, With<Crosshair>>,
+    mut request_center_cursor: Local<bool>,
+) {
+    let (mut window, mut cursor) = window.into_inner();
+    let mut crosshair_visibility = crosshair.into_inner();
+
+    let is_grabbed = cursor.grab_mode == CursorGrabMode::Locked;
+    let request_grab = mouse_button_input.any_just_pressed([MouseButton::Left, MouseButton::Right]);
+    let request_ungrab = !window.focused || key_input.just_pressed(KeyCode::Escape);
+
+    if !is_grabbed && request_grab && !request_ungrab {
+        *crosshair_visibility = Visibility::Inherited;
+        cursor.grab_mode = CursorGrabMode::Locked;
+        cursor.visible = false;
+
+        // HACK: It appears setting the cursor position in the same frame we're
+        //       locking it is not possible, so we're delaying it by a frame.
+        *request_center_cursor = true;
+
+        // To prevent other systems (such as `place_break_blocks`)
+        // from seeing the mouse button inputs, clear the state here.
+        mouse_button_input.clear();
+    }
+
+    if is_grabbed && *request_center_cursor {
+        // Set the cursor position to the middle of the window,
+        // so when it is ungrabbed again it'll reappear there.
+        let center = window.resolution.size() / 2.;
+        window.set_cursor_position(Some(center));
+        *request_center_cursor = false; // Only do this once.
+    }
+
+    if is_grabbed && request_ungrab && !request_grab {
+        *crosshair_visibility = Visibility::Hidden;
+        cursor.grab_mode = CursorGrabMode::None;
+        cursor.visible = true;
+    }
+}
+
+pub fn is_cursor_grabbed(cursor: Single<&CursorOptions>) -> bool {
+    cursor.grab_mode == CursorGrabMode::Locked
+}
+
 #[derive(Component, Debug)]
 pub struct CameraFreeLook {
     /// The mouse sensitivity, in radians per pixel.
@@ -32,42 +79,27 @@ impl Default for CameraFreeLook {
     }
 }
 
-pub fn camera_free_look(
-    window: Single<(&Window, &mut CursorOptions)>,
+pub fn camera_look(
     accumulated_mouse_motion: Res<AccumulatedMouseMotion>,
-    mouse_button_input: Res<ButtonInput<MouseButton>>,
-    key_input: Res<ButtonInput<KeyCode>>,
     camera: Single<(&mut Transform, &mut CameraFreeLook)>,
 ) {
-    let (window, mut cursor) = window.into_inner();
-    let (mut transform, mut camera) = camera.into_inner();
+    let (mut transform, mut look) = camera.into_inner();
 
-    if !window.focused || key_input.just_pressed(KeyCode::Escape) {
-        cursor.grab_mode = CursorGrabMode::None;
-        cursor.visible = true;
+    // Ensure the yaw and pitch are initialized once
+    // from the camera transform's current rotation.
+    if !look.initialized {
+        (look.yaw, look.pitch, _) = transform.rotation.to_euler(EulerRot::YXZ);
+        look.initialized = true;
     }
-    if mouse_button_input.any_just_pressed([MouseButton::Left, MouseButton::Right]) {
-        cursor.grab_mode = CursorGrabMode::Locked;
-        cursor.visible = false;
-    }
-
-    if cursor.grab_mode == CursorGrabMode::Locked {
-        // Ensure the yaw and pitch are initialized once
-        // from the camera transform's current rotation.
-        if !camera.initialized {
-            (camera.yaw, camera.pitch, _) = transform.rotation.to_euler(EulerRot::YXZ);
-            camera.initialized = true;
-        }
 
-        // Update the current camera state's internal yaw and pitch.
-        let motion = accumulated_mouse_motion.delta * camera.sensitivity;
-        let (min, max) = camera.pitch_limit.clone().into_inner();
-        camera.yaw = (camera.yaw - motion.x).rem_euclid(TAU); // keep within 0°..360°
-        camera.pitch = (camera.pitch - motion.y).clamp(min, max);
+    // Update the current camera state's internal yaw and pitch.
+    let motion = accumulated_mouse_motion.delta * look.sensitivity;
+    let (min, max) = look.pitch_limit.clone().into_inner();
+    look.yaw = (look.yaw - motion.x).rem_euclid(TAU); // keep within 0°..360°
+    look.pitch = (look.pitch - motion.y).clamp(min, max);
 
-        // Override the camera transform's rotation.
-        transform.rotation = Quat::from_euler(EulerRot::ZYX, 0.0, camera.yaw, camera.pitch);
-    }
+    // Override the camera transform's rotation.
+    transform.rotation = Quat::from_euler(EulerRot::ZYX, 0.0, look.yaw, look.pitch);
 }
 
 // TODO: Make it possible to attach this to any entity, such as the player,
@@ -109,14 +141,10 @@ impl Default for CameraNoClip {
 
 pub fn noclip_controller(
     time: Res<Time<Real>>,
-    cursor: Single<&mut CursorOptions>,
     key_input: Res<ButtonInput<KeyCode>>,
-    camera: Single<(&mut Transform, &mut CameraNoClip)>,
+    camera: Single<(&mut Transform, &CameraNoClip)>,
 ) {
     let (mut transform, noclip) = camera.into_inner();
-    if cursor.grab_mode != CursorGrabMode::Locked {
-        return;
-    }
 
     #[rustfmt::skip]
     let movement = {
@@ -139,3 +167,32 @@ pub fn noclip_controller(
         transform.translation += movement.z * dt * forward;
     }
 }
+
+#[derive(Component)]
+pub struct Crosshair;
+
+pub fn setup_crosshair(mut commands: Commands, asset_server: Res<AssetServer>) {
+    commands.spawn((
+        Node {
+            width: percent(100),
+            height: percent(100),
+            align_items: AlignItems::Center,
+            justify_content: JustifyContent::Center,
+            ..default()
+        },
+        children![(
+            Crosshair,
+            Node {
+                width: px(64),
+                height: px(64),
+                ..default()
+            },
+            ImageNode {
+                image: asset_server.load("crosshair.png"),
+                ..default()
+            },
+            // Hidden by default, because cursor shouldn't be grabbed at startup either.
+            Visibility::Hidden,
+        )],
+    ));
+}

src/main.rs

@@ -1,34 +1,43 @@
 use bevy::prelude::*;
 
-mod free_camera;
-use free_camera::*;
+mod block;
+mod camera;
+mod placement;
+
+use block::*;
+use camera::*;
+use placement::*;
 
 fn main() {
+    #[rustfmt::skip]
     App::new()
         .add_plugins(DefaultPlugins)
-        .add_systems(Startup, setup)
-        .add_systems(Update, (camera_free_look, noclip_controller).chain())
+
+        .add_systems(Startup, setup_crosshair)
+        .add_systems(Startup, setup_blocks)
+        .add_systems(Startup, setup_scene.after(setup_blocks))
+
+        .add_systems(Update, cursor_grab)
+        .add_systems(Update, camera_look.after(cursor_grab).run_if(is_cursor_grabbed))
+        .add_systems(Update, noclip_controller.after(camera_look).run_if(is_cursor_grabbed))
+
+        // This system requires the camera's `GlobalTransform`, so for
+        // a most up-to-date value, run it right after it's been updated.
+        .add_systems(PostUpdate, place_break_blocks.after(TransformSystems::Propagate))
+
         .run();
 }
 
-fn setup(
-    mut commands: Commands,
-    mut meshes: ResMut<Assets<Mesh>>,
-    mut materials: ResMut<Assets<StandardMaterial>>,
-) {
-    // circular base
-    commands.spawn((
-        Mesh3d(meshes.add(Circle::new(4.0))),
-        MeshMaterial3d(materials.add(Color::WHITE)),
-        Transform::from_rotation(Quat::from_rotation_x(-std::f32::consts::FRAC_PI_2)),
-    ));
-    // cube
+fn setup_scene(mut commands: Commands, mut blocks: Blocks) {
+    // light
     commands.spawn((
-        Mesh3d(meshes.add(Cuboid::new(1.0, 1.0, 1.0))),
-        MeshMaterial3d(materials.add(Color::srgb_u8(124, 144, 255))),
-        Transform::from_xyz(0.0, 0.5, 0.0),
+        Camera3d::default(),
+        Transform::from_xyz(-2.5, 4.5, 9.0).looking_at(Vec3::ZERO, Vec3::Y),
+        CameraFreeLook::default(),
+        CameraNoClip::default(),
     ));
-    // light
+
+    // camera
     commands.spawn((
         PointLight {
             shadows_enabled: true,
@@ -36,11 +45,11 @@ fn setup(
         },
         Transform::from_xyz(4.0, 8.0, 4.0),
     ));
-    // camera
-    commands.spawn((
-        Camera3d::default(),
-        Transform::from_xyz(-2.5, 4.5, 9.0).looking_at(Vec3::ZERO, Vec3::Y),
-        CameraFreeLook::default(),
-        CameraNoClip::default(),
-    ));
+
+    // blocks
+    for x in -8..8 {
+        for z in -8..8 {
+            blocks.spawn(IVec3::new(x, 0, z));
+        }
+    }
 }

src/placement.rs

@@ -0,0 +1,48 @@
+use bevy::prelude::*;
+use bevy::window::{CursorGrabMode, CursorOptions};
+
+use crate::block::*;
+
+pub fn place_break_blocks(
+    mut commands: Commands,
+    mut blocks: Blocks,
+    mut ray_cast: MeshRayCast,
+    mouse_button_input: Res<ButtonInput<MouseButton>>,
+    window: Single<(&Window, &CursorOptions)>,
+    camera: Single<(&GlobalTransform, &Camera)>,
+    block_lookup: Query<&Transform, With<Block>>,
+) {
+    if !mouse_button_input.any_just_pressed([MouseButton::Left, MouseButton::Right]) {
+        return; // only run this system when left or right mouse button is pressed
+    }
+
+    let (window, cursor) = window.into_inner();
+    let (cam_transform, camera) = camera.into_inner();
+
+    let ray = if cursor.grab_mode == CursorGrabMode::Locked {
+        Ray3d::new(cam_transform.translation(), cam_transform.forward())
+    } else if let Some(cursor_pos) = window.cursor_position() {
+        camera.viewport_to_world(cam_transform, cursor_pos).unwrap()
+    } else {
+        return; // cursor outside window area
+    };
+
+    let settings = &MeshRayCastSettings::default();
+    let Some((block, hit)) = ray_cast.cast_ray(ray, settings).first() else {
+        return; // ray didn't hit anything
+    };
+    let Ok(block_transform) = block_lookup.get(*block) else {
+        return; // entity hit is not a block
+    };
+
+    if mouse_button_input.just_pressed(MouseButton::Left) {
+        // Destroy the block clicked.
+        commands.entity(*block).despawn();
+    } else if mouse_button_input.just_pressed(MouseButton::Right) {
+        // Create a new block next to the one that was just clicked.
+        let pos = block_transform.translation.floor().as_ivec3();
+        // FIXME: This only works for axis-aligned normals.
+        let offset = hit.normal.normalize().round().as_ivec3();
+        blocks.spawn(pos + offset);
+    }
+}