Add camera look controls

src/free_camera.rs

@@ -0,0 +1,71 @@
+use std::f32::consts::TAU;
+
+use bevy::input::mouse::AccumulatedMouseMotion;
+use bevy::prelude::*;
+use bevy::window::{CursorGrabMode, CursorOptions};
+
+#[derive(Component, Debug)]
+pub struct CameraFreeLook {
+    /// The mouse sensitivity, in radians per pixel.
+    pub sensitivity: Vec2,
+    /// How far the camera can be tilted up and down.
+    pub pitch_limit: std::ops::RangeInclusive<f32>,
+
+    /// Upon initialization, `pitch` and `yaw` will
+    /// be set from the camera transform's rotation.
+    initialized: bool,
+    /// The current yaw (right/left) of the camera, in radians.
+    pub yaw: f32,
+    /// The current pitch (tilt) of the camera, in radians.
+    pub pitch: f32,
+}
+
+impl Default for CameraFreeLook {
+    fn default() -> Self {
+        Self {
+            sensitivity: Vec2::splat(0.2).map(f32::to_radians),
+            pitch_limit: -(TAU / 4.0)..=(TAU / 4.0),
+            initialized: false,
+            yaw: 0.0,
+            pitch: 0.0,
+        }
+    }
+}
+
+pub fn camera_free_look(
+    window: Single<(&Window, &mut CursorOptions)>,
+    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();
+
+    if !window.focused || key_input.just_pressed(KeyCode::Escape) {
+        cursor.grab_mode = CursorGrabMode::None;
+        cursor.visible = 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 delta = accumulated_mouse_motion.delta * camera.sensitivity;
+        let (min, max) = camera.pitch_limit.clone().into_inner();
+        camera.yaw = (camera.yaw - delta.x).rem_euclid(TAU); // keep within 0°..360°
+        camera.pitch = (camera.pitch - delta.y).clamp(min, max);
+
+        // Override the camera transform's rotation.
+        transform.rotation = Quat::from_euler(EulerRot::ZYX, 0.0, camera.yaw, camera.pitch);
+    }
+}

src/main.rs

@@ -1,9 +1,13 @@
 use bevy::prelude::*;
 
+mod free_camera;
+use free_camera::*;
+
 fn main() {
     App::new()
         .add_plugins(DefaultPlugins)
         .add_systems(Startup, setup)
+        .add_systems(Update, camera_free_look)
         .run();
 }
 
@@ -36,5 +40,6 @@ fn setup(
     commands.spawn((
         Camera3d::default(),
         Transform::from_xyz(-2.5, 4.5, 9.0).looking_at(Vec3::ZERO, Vec3::Y),
+        CameraFreeLook::default(),
     ));
 }