vetovoima - update gravity visuals

update_gravity_visuals.rs

fn update_gravity_visuals(
    mut visuals_query: Query<(&mut Path, &mut DrawMode, &mut GravityRing)>,
    gravity_source: Res<GravitySource>,
) {
    let level_bounds_radius_pixels = LEVEL_BOUNDS_RADIUS_METERS * PIXELS_PER_METER;
    let gravity_source_radius_pixels = GRAVITY_SOURCE_RADIUS_METERS * PIXELS_PER_METER;
    let min_radius = gravity_source_radius_pixels;
    // fade to nothing just before the ring hits the terrain
    let max_radius = level_bounds_radius_pixels;
    

    for (mut path, mut draw_mode, mut ring) in visuals_query.iter_mut() {
        let current_radius = ring.0;
        // reset the radius at the inner or outer edge of the world bounds if outside the bounds
        let bounded_radius = if current_radius < min_radius {
            max_radius
        } else if current_radius > max_radius {
            min_radius
        } else {
            current_radius
        };

        // grow or shrink the ring based on gravity
        let radius_force_ratio = PIXELS_PER_METER / for;
        let next_radius = bounded_radius + (gravity_source.force * radius_force_ratio);
        // solid when close to the gravity source, transparent when far away
        let opacity = (1.0 - (next_radius / max_radius)).max(0.0);
        // dimmer when transparent
        let lightness = 0.35 + (opacity / 2.0);
        // a little subdued even when close to the gravity source
        let capped_opacity = opacity * 0.8;

        let next_shape = shapes::Circle {
            radius: next_radius,
            center: Vec2::ZERO,
        };
        let next_draw_mode = DrawMode::Stroke(StrokeMode {
            options: StrokeOptions::DEFAULT,
            color: Color::hsla(220.0, 1.0, lightness, capped_opacity),
        });

        ring.0 = next_radius;
        *path = ShapePath::build_as(&next_shape);
        *draw_mode = next_draw_mode;
    }
}