How to detect mouse movement over node while button is pressed?

Question

Problem

You can add an event listener to a node which detects mouse movement over it. This doesn't work if a mouse button was pressed before you moved over the node.

Question

Does anyone know how to detect mouse movement while the button is pressed? So far I've only found a solution by using the MOUSE_DRAGGED event and then instead of using getSource() using getPickResult() and evaluating the PickResult data.

Here's the code including Uluk's solution. The old and new solution are switchable via the useNewVersion (Uluk's version) boolean:

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.input.MouseEvent;
import javafx.scene.input.PickResult;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.Pane;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class Main extends Application {

    boolean useNewVersion= true;

    int rows = 10;
    int columns = 20;
    double width = 1024;
    double height = 768;

    @Override
    public void start(Stage primaryStage) {
        try {
            BorderPane root = new BorderPane();

            // create grid
            Grid grid = new Grid( columns, rows, width, height);

            MouseGestures mg = new MouseGestures();

            // fill grid
            for (int row = 0; row < rows; row++) {
                for (int column = 0; column < columns; column++) {

                    Cell cell = new Cell(column, row);

                    mg.makePaintable(cell);

                    grid.add(cell, column, row);
                }
            }

            root.setCenter(grid);

            // create scene and stage
            Scene scene = new Scene(root, width, height);
            scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
            primaryStage.setScene(scene);
            primaryStage.show();



        } catch (Exception e) {
            e.printStackTrace();
        }
    }

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

    private class Grid extends Pane {

        int rows;
        int columns;

        double width;
        double height;

        Cell[][] cells;

        public Grid( int columns, int rows, double width, double height) {

            this.columns = columns;
            this.rows = rows;
            this.width = width;
            this.height = height;

            cells = new Cell[rows][columns];

        }

        /**
         * Add cell to array and to the UI.
         */
        public void add(Cell cell, int column, int row) {

            cells[row][column] = cell;

            double w = width / columns;
            double h = height / rows;
            double x = w * column;
            double y = h * row;

            cell.setLayoutX(x);
            cell.setLayoutY(y);
            cell.setPrefWidth(w);
            cell.setPrefHeight(h);

            getChildren().add(cell);

        }

    }

    private class Cell extends StackPane {

        int column;
        int row;

        public Cell(int column, int row) {

            this.column = column;
            this.row = row;

            getStyleClass().add("cell");

            Label label = new Label(this.toString());

            getChildren().add(label);
        }

        public void highlight() {
            getStyleClass().add("cell-highlight");
        }

        public void unhighlight() {
            getStyleClass().remove("cell-highlight");
        }

        public String toString() {
            return this.column + "/" + this.row;
        }
    }

    public class MouseGestures {

        public void makePaintable( Node node) {

            if( useNewVersion) {

                node.setOnMousePressed( onMousePressedEventHandler);
                node.setOnDragDetected( onDragDetectedEventHandler);
                node.setOnMouseDragEntered( onMouseDragEnteredEventHandler);

            } else {

                node.setOnMousePressed( onMousePressedEventHandler);
                node.setOnMouseDragged( onMouseDraggedEventHandler);
                node.setOnMouseReleased( onMouseReleasedEventHandler);

            }

        }

        /* old version */

        EventHandler<MouseEvent> onMousePressedEventHandler = event -> {

            Cell cell = (Cell) event.getSource();

            if( event.isPrimaryButtonDown()) {
                cell.highlight();
            } else if( event.isSecondaryButtonDown()) {
                cell.unhighlight();
            }
        };

        EventHandler<MouseEvent> onMouseDraggedEventHandler = event -> {

            PickResult pickResult = event.getPickResult();
            Node node = pickResult.getIntersectedNode();

            if( node instanceof Cell) {

                Cell cell = (Cell) node;

                if( event.isPrimaryButtonDown()) {
                    cell.highlight();
                } else if( event.isSecondaryButtonDown()) {
                    cell.unhighlight();
                }       

            }

        };

        EventHandler<MouseEvent> onMouseReleasedEventHandler = event -> {
        };

        EventHandler<MouseEvent> onDragDetectedEventHandler = event -> {

            Cell cell = (Cell) event.getSource();
            cell.startFullDrag();

        };

        EventHandler<MouseEvent> onMouseDragEnteredEventHandler = event -> {

            Cell cell = (Cell) event.getSource();

            if( event.isPrimaryButtonDown()) {
                cell.highlight();
            } else if( event.isSecondaryButtonDown()) {
                cell.unhighlight();
            }       

        };

    }

}

In the end you should be able to paint via primary mouse button and erase the paint via secondary mouse button:

Answer 1

One solution is to add an event filter to the scene which enables the sourceNode.startFullDrag(). This will work even if you start dragging the mouse outside of your canvas (if you want any space without nodes in your application).

Like this:

scene.addEventFilter(MouseEvent.DRAG_DETECTED , new EventHandler<MouseEvent>() {
    @Override
    public void handle(MouseEvent mouseEvent) {
        scene.startFullDrag();
    }
});

And then you could:

node.setOnMouseDragEntered(new EventHandler<MouseEvent>() {
    @Override
    public void handle(MouseEvent event) {
        led.setOn(true);
    } 
});

Answer 2

The (source) node which handles the initial DRAG_DETECTED event should invoke sourceNode.startFullDrag(), then the target node will able to handle one of MouseDragEvents, for instance MOUSE_DRAG_OVER or MOUSE_DRAG_ENTERED event with respective targetNode.setOn<MouseDragEvent>() method.