how to zoom in to a sprite in bevy

Question

I wanted to implement zooming in my 2d bevy game. After some code browsing I found out that Camera2dBundle uses OrthographicProjection by default and can not zoom in as required.

I tried using Camera3dBundle which does define projection: PerspectiveProjection by default but my sprite seems to disappear from the scene.

Could you give me some pointers to what I'm doing wrong? I have included some test code below.

Thanks

use bevy::prelude::*;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup)
        .add_system(zoom_in)
        .run();
}

fn setup(
    mut commands: Commands
    ) {
        commands.spawn_bundle(Camera3dBundle {
            transform: Transform::from_xyz(0., 0., 1000.).looking_at(Vec3::ZERO, Vec3::Z),
            ..Default::default()
        });
        
        commands.spawn_bundle(SpriteBundle {
           sprite: Sprite { custom_size: Some(Vec2 { x: 50., y: 50. }), ..Default::default()},
           ..Default::default()
        });
}

pub fn zoom_in(mut query: Query<&mut Transform, With<Camera>>, time: Res<Time>) {
    for mut transform in query.iter_mut() {
        transform.translation.z -= 100. * time.delta_seconds();

        warn!("{}", transform.translation.z);
    }
}

Answer 1

You do not see the sprite, because you apparently look at it from the wrong side. If you have a 2D scene I would advise you to stick to the Camera2DBundle.

Contrary to what you stated in your question, in order to zoom you can set the scale of OrthographicProjection like so:

use bevy::prelude::*;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup)
        .add_system(zoom_in)
        .run();
}

fn setup(
    mut commands: Commands
    ) {
        commands.spawn_bundle(Camera2dBundle::default());
        commands.spawn_bundle(SpriteBundle {
           sprite: Sprite { custom_size: Some(Vec2 { x: 50., y: 50. }), ..Default::default()},
           ..Default::default()
        });
}

pub fn zoom_in(mut query: Query<&mut OrthographicProjection, With<Camera>>, time: Res<Time>) {
    for mut projection in query.iter_mut() {
        projection.scale -= 0.1 * time.delta_seconds();

        println!("Current zoom scale: {}", projection.scale);
    }
}

Note that you might want to implement logarithmic zoom, so that your zoom does "feel" linear and does not speed up approaching infinity when the scale approaches zero.

Here is a sample using logarithmic zoom:

use bevy::prelude::*;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup)
        .add_system(zoom_in)
        .run();
}

fn setup(
    mut commands: Commands
    ) {
        commands.spawn_bundle(Camera2dBundle::default());
        commands.spawn_bundle(SpriteBundle {
           sprite: Sprite { custom_size: Some(Vec2 { x: 50., y: 50. }), ..Default::default()},
           ..Default::default()
        });
}

pub fn zoom_in(mut query: Query<&mut OrthographicProjection, With<Camera>>, time: Res<Time>) {
    for mut projection in query.iter_mut() {
        let mut log_scale = projection.scale.ln();
        log_scale -= 0.1 * time.delta_seconds();
        projection.scale = log_scale.exp();

        println!("Current zoom scale: {}", projection.scale);
    }
}