Multi-Touch Pinch Zoom Bevy System Example

zoom_pinch_system.rs

#[allow(clippy::type_complexity, clippy::too_many_arguments)]
pub fn pinch_system(
    touches: Res<Touches>,
    mut touch_e: EventReader<TouchInput>,
    time: Res<Time>,
    mut cam_query: Query<&mut OrthographicProjection, With<Camera>>,
    mut multitouch_distance: Local<f32>,
) {
    let mut zoom_amount: f32 = 0.0;

    for _e in touch_e.read() {
        if touches.iter().count() == 2 {
            let first = touches
                .first_pressed_position()
                .unwrap_or(Vec2 { x: 0.0, y: 0.0 });

            for touch in touches.iter() {
                if touch.position() != first {
                    let diff2 = distance_between_vecs(&touch.position(), &first);
                    if diff2 > 110.0 {
                        if (*multitouch_distance - diff2).abs() > 2.0 {
                            if *multitouch_distance == 0.0 {
                            } else if *multitouch_distance > diff2 {
                                zoom_amount = 0.25;
                                info!("zooming out");
                            } else {
                                zoom_amount = -0.25;
                                info!("zooming in");
                            }
                        }

                        *multitouch_distance = diff2;
                    }
                }
            }

            if zoom_amount != 0.0 {
                let time_adjusted = if time.delta_seconds() > 0.01 {
                    0.01
                } else {
                    time.delta_seconds()
                };
                for mut ortho in cam_query.iter_mut() {
                    ortho.scale += zoom_amount * time_adjusted * 30.0;
                    if ortho.scale > ZOOM_OUT_MAX {
                        ortho.scale = ZOOM_OUT_MAX;
                    } else if ortho.scale < ZOOM_IN_MAX {
                        ortho.scale = ZOOM_IN_MAX;
                    }
                }
            }
        } else {
            *multitouch_distance = 0.0;
        }
    }
}