Example of a JavaFX Application controlling a RGB LED Strip through communicating with an Arduino Uno to create a cheap DIY ambient backlight (single-color).

AmbilightControl.java

package de.molaynoxx.ambilightcontrol;

import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;
import javafx.application.Application;
import javafx.application.Platform;
import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.collections.FXCollections;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.control.Button;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.paint.Paint;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;
import javafx.util.Callback;
import org.bytedeco.javacv.*;

import java.awt.image.BufferedImage;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.Enumeration;

import static org.bytedeco.javacpp.avutil.*;
import static org.bytedeco.javacpp.avcodec.*;

public class AmbilightControl extends Application {

    private SerialPort serialPort;
    private OutputStream output;
    private int color = 0;
    private ObjectProperty<Paint> colorDisplayFill = new SimpleObjectProperty<>();
    private boolean calculateScreenAverage = false;
    public static final FFmpegFrameGrabber grabber = new FFmpegFrameGrabber("video=screen-capture-recorder");
    public static final Java2DFrameConverter converter = new Java2DFrameConverter();

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

    @Override
    public void start(Stage primaryStage) throws Exception {
        Enumeration portEnum = CommPortIdentifier.getPortIdentifiers();

        ArrayList<CommPortIdentifier> comPorts = new ArrayList<>();

        while (portEnum.hasMoreElements()) {
            comPorts.add((CommPortIdentifier) portEnum.nextElement());
        }

        primaryStage.setTitle("Ambilight Control");
        VBox hbSelectRoot = new VBox();
        Scene sceneSelectPort = new Scene(hbSelectRoot, 200, 40);
        primaryStage.setResizable(false);

        Callback<ListView<CommPortIdentifier>, ListCell<CommPortIdentifier>> cellFactory = new Callback<ListView<CommPortIdentifier>, ListCell<CommPortIdentifier>>() {
            @Override
            public ListCell<CommPortIdentifier> call(ListView<CommPortIdentifier> param) {
                return new ListCell<CommPortIdentifier>() {

                    @Override
                    protected void updateItem(CommPortIdentifier item, boolean empty) {
                        super.updateItem(item, empty);
                        if(!empty) setText(item.getName());
                    }

                };
            }
        };

        ComboBox<CommPortIdentifier> portSelector = new ComboBox<>();
        portSelector.setCellFactory(cellFactory);
        portSelector.setButtonCell(cellFactory.call(null));
        portSelector.setItems(FXCollections.observableArrayList(comPorts));
        portSelector.getSelectionModel().select(0);

        Button buttonSelect = new Button("Select");
        buttonSelect.setOnAction(action -> loadProgram(primaryStage, portSelector.getSelectionModel().getSelectedItem()));

        buttonSelect.prefWidthProperty().bind(hbSelectRoot.widthProperty());
        portSelector.prefWidthProperty().bind(hbSelectRoot.widthProperty());
        hbSelectRoot.getChildren().addAll(portSelector, buttonSelect);

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

    private void loadProgram(Stage primaryStage, CommPortIdentifier comPort) {
        VBox rootPane = new VBox();
        Scene mainScene = new Scene(rootPane, 400, 200);
        primaryStage.setResizable(false);
        primaryStage.setScene(mainScene);

        ToggleGroup group = new ToggleGroup();

        RadioButton rbUseColor = new RadioButton("Use selected color");
        rbUseColor.setToggleGroup(group);
        rbUseColor.setSelected(true);

        RadioButton rbUseScreenAverage = new RadioButton("Use average screen color");
        rbUseScreenAverage.setToggleGroup(group);

        HBox hbRadioButtons = new HBox();
        VBox.setMargin(hbRadioButtons, new Insets(10, 10, 10, 10));
        hbRadioButtons.setSpacing(20);
        hbRadioButtons.getChildren().addAll(rbUseColor, rbUseScreenAverage);

        ColorPicker colorPicker = new ColorPicker(Color.BLACK);
        colorPicker.prefWidthProperty().bind(rootPane.widthProperty().subtract(20));
        VBox.setMargin(colorPicker, new Insets(0, 10, 0, 10));
        rootPane.getChildren().addAll(hbRadioButtons, colorPicker);

        colorDisplayFill.set(colorPicker.getValue());
        colorPicker.setOnAction(action -> {
            if(rbUseColor.isSelected()) {
                Color c = colorPicker.getValue();
                color = getIntFromColor((int) (c.getRed() * 255), (int) (c.getGreen() * 255), (int) (c.getBlue() * 255));
                colorDisplayFill.set(c);
            }
        });
        rbUseColor.setOnAction(action -> {
            rbUseScreenAverage.setDisable(true);
            calculateScreenAverage = false;
            new Thread(() -> {
                try {
                    Thread.sleep(100);
                    grabber.stop();
                } catch (Exception ignored) {}
                Platform.runLater(() -> {
                    Color c = colorPicker.getValue();
                    color = getIntFromColor((int) (c.getRed() * 255), (int) (c.getGreen() * 255), (int) (c.getBlue() * 255));
                    colorDisplayFill.set(c);
                    rbUseScreenAverage.setDisable(false);
                });
            }).start();
        });
        rbUseScreenAverage.setOnAction(action -> {
            try {
                grabber.start();
            } catch (FrameGrabber.Exception ignored) {}
            calculateScreenAverage = true;
        });

        Rectangle colorDisplay = new Rectangle();
        colorDisplay.widthProperty().bind(rootPane.widthProperty().subtract(40));
        colorDisplay.setHeight(100);
        colorDisplay.fillProperty().bind(colorDisplayFill);
        rootPane.getChildren().add(colorDisplay);
        VBox.setMargin(colorDisplay, new Insets(20, 20, 20, 20));

        try {
            serialPort = (SerialPort) comPort.open(this.getClass().getName(), 2000);

            serialPort.setSerialPortParams(9600,
                    SerialPort.DATABITS_8,
                    SerialPort.STOPBITS_1,
                    SerialPort.PARITY_NONE);

            output = serialPort.getOutputStream();

            grabber.setFormat("dshow");
            grabber.setFrameRate(30);
            grabber.setVideoBitrate(5000);
            grabber.setPixelFormat(AV_PIX_FMT_BGR24);
            grabber.setVideoCodec(AV_CODEC_ID_RAWVIDEO);

            final Thread thSend = new Thread(() -> {
                while(true) {
                    try {
                        if(calculateScreenAverage) {
                            calculateAverageScreenColor();
                        }
                        output.write(0xFF);
                        output.write(0xFF & (byte) (color >> 16 & 0xFF));
                        output.write(0xFF & (byte) (color >> 8 & 0xFF));
                        output.write(0xFF & (byte) (color & 0xFF));
                        Thread.sleep(1);
                    } catch (Exception e) {
                        break;
                    }
                }
            });
            thSend.setDaemon(true);
            thSend.start();

            primaryStage.setOnCloseRequest(event -> {
                thSend.interrupt();
                new Thread(() -> {
                    try {
                        Thread.sleep(250);
                        grabber.stop();
                    } catch (Exception ignored) {}
                }).start();
            });

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

    public void calculateAverageScreenColor() {
        try {
            Frame grabbedFrame = grabber.grabImage();
            BufferedImage frame = converter.convert(grabbedFrame);

            long rSum = 0, gSum = 0, bSum = 0;
            int width = frame.getWidth();
            int height = frame.getHeight();
            int rgb;
            for(int x = 0; x < width; x += 3) {
                for(int y = 0; y < height; y += 3) {
                    rgb = frame.getRGB(x, y);
                    bSum += rgb & 0xFF;
                    gSum += (rgb & 0xFF00) >> 8;
                    rSum += (rgb & 0xFF0000) >> 16;
                }
            }

            rSum /= width * height / 9;
            gSum /= width * height / 9;
            bSum /= width * height / 9;

            color = getIntFromColor((int) rSum, (int) gSum, (int) bSum);

            final Color c = Color.rgb((int) rSum, (int) gSum, (int) bSum);
            Platform.runLater(() -> {
                colorDisplayFill.set(c);
            });
        } catch (FrameGrabber.Exception ex) {
            ex.printStackTrace();
        }
    }

    public int getIntFromColor(int red, int green, int blue){
        return (red << 16) + (green << 8) + blue;
    }

    @Override
    public void stop() throws Exception {
        super.stop();
        if (serialPort != null) {
            serialPort.close();
        }
    }
}