Method clean

src/main/java/field/graphics/Window.java:1320–1342

(long window)

        public Drop(String[] files, MouseState mouseState, KeyboardState keyboardState) {
            this.files = files;
            this.mouseState = mouseState;
            this.keyboardState = keyboardState;
        }

        @Override
        public Optional<Vec2> position() {
            if (mouseState == null) return Optional.empty();
            return mouseState.position();
        }
    }

    static public class Event<T> extends AsMapDelegator {
        public final T before;
        public final T after;

        public final Dict properties = new Dict();

        public Event(T before, T after) {
            this.before = before;
            this.after = after;
        }

        public String toString() {
            return "ev<" + before + "->" + after + ">";
        }