JavaFX key interruptions?

Question

I\'m trying to write a game in JavaFX but I\'m having a slight issue with it and that\'s the key listeners getting interrupted by other key presses. I\'m using scene.s

Answer 1

I would make a set of all keys currently pressed and just check them in a timer. It doesn't eat many cpu cycles on my old machine. In motion it's 5%, but 0% when no key is pressed.

For a possibly faster solution use an ObservableSet and start and stop actions when a key is added or removed.

package keytest;

import javafx.animation.Animation;
import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.collections.FXCollections;
import javafx.collections.ObservableSet;
import javafx.collections.SetChangeListener;
import javafx.scene.Scene;
import javafx.scene.input.KeyCode;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;

public class KeyTest extends Application {

    @Override
    public void start(Stage primaryStage) {
        ObservableSet downKeys = FXCollections.observableSet();

        Circle circle = new Circle(10);
        Pane root = new Pane(circle);
        Scene scene = new Scene(root, 500, 500);

        scene.setOnKeyPressed(evt->{
            downKeys.add(evt.getCode());
        });

        scene.setOnKeyReleased(evt->{
            downKeys.remove(evt.getCode());
        });


        Timeline timer = new Timeline(new KeyFrame(
            javafx.util.Duration.millis(16), ae -> {
                downKeys.stream().parallel().forEach(kc -> {
                    Platform.runLater(() -> {//why?
                        switch(kc){
                            case UP: circle.setTranslateY(circle.getTranslateY()-2);
                                break;
                            case DOWN: circle.setTranslateY(circle.getTranslateY()+2);
                                break;
                            case LEFT: circle.setTranslateX(circle.getTranslateX()-2);
                                break;
                            case RIGHT: circle.setTranslateX(circle.getTranslateX()+2);
                                break;
                        }
                    });
                });
            }));
        timer.setCycleCount(Animation.INDEFINITE);
        timer.play();

        //I think this might be faster
        downKeys.addListener((SetChangeListener.Change change) -> {
            if (change.wasAdded()){
                System.out.println("start action "+change.getElementAdded());
            }
            if (change.wasRemoved()){
                System.out.println("stop action "+change.getElementRemoved());
            }
        });

        primaryStage.setScene(scene);
        primaryStage.show();
    }

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

}

I'm thinking the parallel is stupid and the Platform.runLater costs more than the threading of +2 or -2 . But hey, java8 that's why