projection_zoom.rs

//! Shows how to zoom orthographic and perspective projection cameras.

use std::{f32::consts::PI, ops::Range};

use bevy::{input::mouse::AccumulatedMouseScroll, prelude::*, render::camera::ScalingMode};

#[derive(Debug, Default, Resource)]
struct CameraSettings {
    // Clamp fixed vertical scale to this range
    pub orthographic_zoom_range: Range<f32>,
    // Multiply mouse wheel inputs by this factor
    pub orthographic_zoom_speed: f32,
    // Clamp field of view to this range
    pub perspective_zoom_range: Range<f32>,
    // Multiply mouse wheel inputs by this factor
    pub perspective_zoom_speed: f32,
}

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .init_resource::<CameraSettings>()
        .add_systems(Startup, (setup, instructions))
        .add_systems(Update, (switch_projection, zoom))
        .run();
}

/// Set up a simple 3D scene
fn setup(
    asset_server: Res<AssetServer>,
    mut camera_settings: ResMut<CameraSettings>,
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    // Perspective projections use field of view, expressed in radians. We would
    // normally not set it to more than π, which represents a 180° FOV.
    let min_fov = PI / 5.;
    let max_fov = PI - 0.2;

    // In orthographic projections, we specify sizes in world units. The below values
    // are very roughly similar to the above FOV settings, in terms of how "far away"
    // the subject will appear when used with FixedVertical scaling mode.
    let min_zoom = 5.0;
    let max_zoom = 150.0;

    camera_settings.orthographic_zoom_range = min_zoom..max_zoom;
    camera_settings.orthographic_zoom_speed = 1.0;
    camera_settings.perspective_zoom_range = min_fov..max_fov;
    // Changes in FOV are much more noticeable due to its limited range in radians
    camera_settings.perspective_zoom_speed = 0.05;

    commands.spawn((
        Name::new("Camera"),
        Camera3dBundle {
            projection: OrthographicProjection {
                scaling_mode: ScalingMode::FixedVertical(
                    camera_settings.orthographic_zoom_range.start,
                ),
                ..OrthographicProjection::default_3d()
            }
            .into(),
            transform: Transform::from_xyz(5.0, 5.0, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
            ..default()
        },
    ));

    commands.spawn((
        Name::new("Plane"),
        PbrBundle {
            mesh: meshes.add(Plane3d::default().mesh().size(5.0, 5.0)),
            material: materials.add(StandardMaterial {
                base_color: Color::srgb(0.3, 0.5, 0.3),
                // Turning off culling keeps the plane visible when viewed from beneath.
                cull_mode: None,
                ..default()
            }),
            ..default()
        },
    ));

    commands.spawn((
        Name::new("Fox"),
        SceneBundle {
            scene: asset_server
                .load(GltfAssetLabel::Scene(0).from_asset("models/animated/Fox.glb")),
            // Note: the scale adjustment is purely an accident of our fox model, which renders
            // HUGE unless mitigated!
            transform: Transform::from_translation(Vec3::splat(0.0)).with_scale(Vec3::splat(0.025)),
            ..default()
        },
    ));

    commands.spawn((
        Name::new("Light"),
        PointLightBundle {
            transform: Transform::from_xyz(3.0, 8.0, 5.0),
            ..default()
        },
    ));
}

fn instructions(mut commands: Commands) {
    commands
        .spawn((
            Name::new("Instructions"),
            NodeBundle {
                style: Style {
                    align_items: AlignItems::Start,
                    flex_direction: FlexDirection::Column,
                    justify_content: JustifyContent::Start,
                    width: Val::Percent(100.),
                    ..default()
                },
                ..default()
            },
        ))
        .with_children(|parent| {
            parent.spawn(TextBundle::from_section(
                "Scroll mouse wheel to zoom in/out",
                TextStyle::default(),
            ));
            parent.spawn(TextBundle::from_section(
                "Space: switch between orthographic and perspective projections",
                TextStyle::default(),
            ));
        });
}

fn switch_projection(
    mut camera: Query<&mut Projection, With<Camera>>,
    camera_settings: Res<CameraSettings>,
    keyboard_input: Res<ButtonInput<KeyCode>>,
) {
    let mut projection = camera.single_mut();

    if keyboard_input.just_pressed(KeyCode::Space) {
        // Switch projection type
        *projection = match *projection {
            Projection::Orthographic(_) => Projection::Perspective(PerspectiveProjection {
                fov: camera_settings.perspective_zoom_range.start,
                ..default()
            }),
            Projection::Perspective(_) => Projection::Orthographic(OrthographicProjection {
                scaling_mode: ScalingMode::FixedVertical(
                    camera_settings.orthographic_zoom_range.start,
                ),
                ..OrthographicProjection::default_3d()
            }),
        }
    }
}

fn zoom(
    mut camera: Query<&mut Projection, With<Camera>>,
    camera_settings: Res<CameraSettings>,
    mouse_wheel_input: Res<AccumulatedMouseScroll>,
) {
    let projection = camera.single_mut();

    // Usually, you won't need to handle both types of projection. This is by way of demonstration.
    match projection.into_inner() {
        Projection::Orthographic(ref mut orthographic) => {
            // Get the current scaling_mode value to allow clamping the new value to our zoom range.
            let ScalingMode::FixedVertical(current) = orthographic.scaling_mode else {
                return;
            };
            // Set a new ScalingMode, clamped to a limited range.
            let zoom_level = (current
                + camera_settings.orthographic_zoom_speed * mouse_wheel_input.delta.y)
                .clamp(
                    camera_settings.orthographic_zoom_range.start,
                    camera_settings.orthographic_zoom_range.end,
                );
            orthographic.scaling_mode = ScalingMode::FixedVertical(zoom_level);
        }
        Projection::Perspective(ref mut perspective) => {
            // Adjust the field of view, but keep it within our stated range.
            perspective.fov = (perspective.fov
                + camera_settings.perspective_zoom_speed * mouse_wheel_input.delta.y)
                .clamp(
                    camera_settings.perspective_zoom_range.start,
                    camera_settings.perspective_zoom_range.end,
                );
        }
    }
}