Javafx: ask if there is a node inside the viewport or not?

Question

When using ScrollPane (with scaling transform for scaling), is there an automatic way to get the currently visible nodes in the scene tree (or invisible), for example, event callbacks?

Or do I need to use a separate structure (Quadtree, RTree) to track nodes?

Answer 1

I don't think there is a particularly easy way to do this, but you can use some bindings to get what you need. Here is the basic idea:

import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.beans.binding.ObjectBinding;
import javafx.collections.ListChangeListener;
import javafx.collections.transformation.FilteredList;
import javafx.geometry.Bounds;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.ScrollPane;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Ellipse;
import javafx.scene.shape.Polygon;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;

public class ScrollPaneTracking extends Application {

    @Override
    public void start(Stage primaryStage) {
        Pane pane = new Pane();
        populatePane(pane);
        ScrollPane scrollPane = new ScrollPane();
        scrollPane.setContent(pane);

        ObjectBinding<Bounds> visibleBounds = Bindings.createObjectBinding(() -> {
            Bounds viewportBounds = scrollPane.getViewportBounds();
            Bounds viewportBoundsInScene = scrollPane.localToScene(viewportBounds);
            Bounds viewportBoundsInPane = pane.sceneToLocal(viewportBoundsInScene);
            return viewportBoundsInPane ;
        }, scrollPane.hvalueProperty(), scrollPane.vvalueProperty(), scrollPane.viewportBoundsProperty());


        FilteredList<Node> visibleNodes = new FilteredList<>(pane.getChildren());
        visibleNodes.predicateProperty().bind(Bindings.createObjectBinding(() -> 
            node -> node.getBoundsInParent().intersects(visibleBounds.get()),
            visibleBounds));


        visibleNodes.addListener((ListChangeListener.Change<? extends Node> c) -> {
                visibleNodes.forEach(System.out::println);
                System.out.println();
        });

        Scene scene = new Scene(scrollPane, 600, 400);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private void populatePane(Pane pane) {

        Rectangle rect = new Rectangle(50, 50, 250, 100);
        rect.setFill(Color.CORNFLOWERBLUE);

        Circle circle = new Circle(450, 450, 75);
        circle.setFill(Color.SALMON);

        Polygon triangle = new Polygon(600, 600, 750, 750, 450, 750);
        triangle.setFill(Color.CHARTREUSE);

        Ellipse ellipse = new Ellipse(200, 600, 50, 150);
        ellipse.setFill(Color.DARKORCHID);

        pane.getChildren().addAll(rect, circle, triangle, ellipse);
    }

    public static void main(String[] args) {
        launch(args);
    }
}

- , , , . :

    ObservableSet<Node> visibleNodes = FXCollections.observableSet();
    visibleBounds.addListener((obs, oldBounds, newBounds) -> {
        for (Node node : pane.getChildren() ) {
            if (node.getBoundsInParent().intersects(newBounds)) {
                visibleNodes.add(node);
            } else {
                visibleNodes.remove(node);
            }
        }
    });

    visibleNodes.addListener((SetChangeListener.Change<? extends Node> c) -> {
            visibleNodes.forEach(System.out::println);
            System.out.println();
    });

, , ( ), . visibleBounds, , .