JavaFX - Task - Affichage des pixels retouchés se bloque

GraphicEngine.java

import javafx.concurrent.Service;
import javafx.concurrent.Task;
import javafx.scene.image.PixelReader;
import javafx.scene.paint.Color;

public class GraphicEngine extends Service<Void> {
    Pixel pixel_buffer;
    public int image_width, image_height;
    private PixelReader pixel_reader;

    public Task<Void> createTask() {
        return new Task<Void>() {

            protected Void call() {
                double r, g, b;
                for (int x = 0; x < image_width; x++) {
                    for (int y = 0; y < image_height; y++) {
                        r = pixel_reader.getColor(x, y).getRed() * 255;
                        g = pixel_reader.getColor(x, y).getGreen() * 255;
                        b = pixel_reader.getColor(x, y).getBlue() * 255;

                        pixel_buffer.setAttributes(x, y, Color.rgb((int) (255 - r), (int) (255 - g), (int) (255 - b)));
                    }
                }
                return null;
            }
        };
    }





    // <!-- GRAPHIC TREATMENTS -->
    public void reverseImg() { // Cette fonction n'est jamais appelée : son CODE EST MOMENTANEMENT PLACE DANS createTask > call !!!
        double r, g, b;
        for(int x = 0; x < this.image_width; x++) {
            for(int y = 0; y < this.image_height; y++) {
                r = this.pixel_reader.getColor(x, y).getRed()*255;
                g = this.pixel_reader.getColor(x, y).getGreen()*255;
                b = this.pixel_reader.getColor(x, y).getBlue()*255;
                //this.writable_pixel_writer.setColor(x, y, Color.rgb((int) (255 - r), (int) (255 - g), (int) (255 - b)));
            }
        }
    }

    public void setAttributes(int image_width, int image_height, PixelReader pixel_reader, Pixel pixel_buffer) {
        this.image_width = image_width;
        this.image_height = image_height;
        this.pixel_reader = pixel_reader;
        this.pixel_buffer = pixel_buffer;
    }

    public void setBackgroundColor(Color color) {
        for(int x = 0; x < this.image_width; x++) {
            for (int y = 0; y < this.image_height; y++) {
                //this.writable_pixel_writer.setColor(x, y, color);
            }
        }
    }

    public void setBackgroundColorRandom() {
        for(int x = 0; x < this.image_width; x++) {
            for (int y = 0; y < this.image_height; y++) {
                //this.writable_pixel_writer.setColor(x, y, Color.color(Math.random(), Math.random(), Math.random()));
            }
        }
    }

    public void displayHorGraduation(String type) {
        double w = this.image_width;
        double r = 0, g = 0, b = 0;
        for(int x = 0; x < this.image_width; x++) {
            for (int y = 0; y < this.image_height; y++) {

                if(type.equals("Blanc vers noir")) {
                    //this.writable_pixel_writer.setColor(x, y, Color.color(-x/w + 1, -x/w + 1, -x/w + 1));
                } else if(type.equals("Noir vers blanc")) {
                    //this.writable_pixel_writer.setColor(x, y, Color.color(x/w, x/w, x/w));
                } else if(type.equals("Polychrome")) {

                    if(x >= 0 && x < w/6) {
                        r = 255;
                        g = 1530*x/w;
                    }

                    if(x >= 0 && x < 2*w/6) {
                        b = 0;
                    }

                    if(x >= 2*w/6 && x < 3*w/6) {
                        b = 1530*x/w - 510;
                    }

                    if(x >= 3*w/6 && x < 5*w/6) {
                        b = 255;
                    }

                    if(x >= 5*w/6 && x <= w) {
                        b = -1530*x/w + 1530;
                    }

                    if (x >= w/6 && x < 3*w/6) {
                        g = 255;
                    }

                    if(x >= 3*w/6 && x < 4*w/6) {
                        g = -1530*x/w + 1020;
                    }

                    if(x >= 4*w/6 && x <= w) {
                        g = 0;
                    }

                    if(x >= w/6 && x < 2*w/6) {
                        r = -1530*x/w + 510;
                    }

                    if(x >= 2*w/6 && x < 4*w/6) {
                        r = 0;
                    }

                    if(x >= 4*w/6 && x < 5*w/6) {
                        r = 1530*x/w - 1020;
                    }

                    if(x >= 5*w/6 && x <= w) {
                        r = 255;
                    }

                    //this.writable_pixel_writer.setColor(x, y, Color.color(r/255, g/255, b/255));
                }
            }
        }
    }

    public void displayCircle() {

        double pi = 3.14159;

        double ra = 100, x0 = 200, y0 = 300, x, y;
        double r, g, b;

        double shift = 0;
        double w = 2 * pi;

        for (double width = 0; width < 5; width++) {
            r = 0;
            g = 0;
            b = 0;
            for (double angle = shift; angle <= (w + shift); angle += 0.00001) {
                x = (width + ra) * Math.cos(angle) + x0;
                y = (width + ra) * Math.sin(angle) + y0;

                if (angle >= (0 + shift) && angle < (w / 6 + shift)) {
                    r = 255;
                    g = (1530 * angle / w) + (-1530 / w * shift);
                }

                if (angle >= (0 + shift) && angle < (2 * w / 6) + shift) {
                    b = 0;
                }

                if (angle >= (2 * w / 6 + shift) && angle < (3 * w / 6 + shift)) {
                    b = 1530 * angle / w + (-510 - 1530 * shift / w);
                }

                if (angle >= (3 * w / 6 + shift) && angle < (5 * w / 6 + shift)) {
                    b = 255;
                }

                if (angle >= (5 * w / 6 + shift) && angle <= (w + shift)) {
                    b = -1530 * angle / w + (1530 + 1530 * shift / w);
                }

                if (angle >= (w / 6 + shift) && angle < (3 * w / 6 + shift)) {
                    g = 255;
                }

                if (angle >= (3 * w / 6 + shift) && angle < (4 * w / 6 + shift)) {
                    g = -1530 * angle / w + (1020 + 1530 * shift / w);
                }

                if (angle >= (4 * w / 6 + shift) && angle <= (w + shift)) {
                    g = 0;
                }

                if (angle >= (w / 6 + shift) && angle < (2 * w / 6 + shift)) {
                    r = -1530 * angle / w + (510 + 1530 * shift / w);
                }

                if (angle >= (2 * w / 6 + shift) && angle < (4 * w / 6 + shift)) {
                    r = 0;
                }

                if (angle >= (4 * w / 6 + shift) && angle < (5 * w / 6 + shift)) {
                    r = 1530 * angle / w + (-1020 - 1530 * shift / w);
                }

                if (angle >= (5 * w / 6 + shift) && angle <= (w + shift)) {
                    r = 255;
                }

                //this.writable_pixel_writer.setColor((int) x, (int) y, Color.color(r / 255, g / 255, b / 255));
            }
        }
    }
}

Gui.java

import javafx.collections.FXCollections;
import javafx.embed.swing.SwingFXUtils;
import javafx.geometry.HPos;
import javafx.geometry.Orientation;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.image.*;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.FlowPane;
import javafx.scene.paint.Color;
import javafx.scene.text.Text;
import javafx.stage.FileChooser;
import javafx.stage.Stage;

import javax.imageio.ImageIO;
import java.io.File;
import java.io.IOException;
import java.util.Observable;
import java.util.Observer;

public class Gui extends Scene implements Observer {
    private Stage stage;
    private final String TITLE_FULL_FX = " - GraphicEngine : JAVAFX", TITLE_WITHOUT_FX = " - GraphicEngine : Java AWT";
    private String STAGE_ORIGINAL_TITLE;
    private BorderPane root;
    private GraphicEngine graphic_engine;
    private ColorPicker color_picker;

    // NAV
    private MenuBar menu_bar;

    private Menu file;
    private MenuItem open, save;

    private Menu menu_create_sheet;
    private MenuItem sheet_customized;

    private Menu menu_create_gradation;
    private MenuItem gradation_customized;

    // TOP
    private FlowPane top_pane;
    private TextField img_path;
    private Button button_load_img_from_web;
    private Text or;
    private Button button_load_img_from_local;
    private FileChooser file_chooser;

    // LEFT
    private FlowPane left_pane;
    private Button create_sheet;
    private Text title_creation_img;
    private Label label_width;
    private Label label_height;
    private TextField field_width;
    private TextField field_height;
    private FlowPane creation_img_pane;
    private Button cancel_creation_img;
    private Button continue_creation_img;
    private CheckBox checkbox_random_color_points;
    private Button button_hor_gradation;
    private Button button_draw_circle;

    // CENTER
    private ScrollPane scroll_pane;


    // RIGHT
    private FlowPane right_pane;
    private Button button_reverse_image;

    // BOT
    private FlowPane bot_pane;
    private Button save_img;
    private final String VERSION_WITH_MENU = "Passer à la version avec menu", VERSION_WITH_BUTTONS = "Passer à la version avec boutons";
    private Button switch_mode;


    // DIALOG
    private Dialog dialog_gradation;
    private FlowPane dialog_flowpane;
    private Label dialog_label_width;
    private Label dialog_label_height;
    private TextField dialog_field_width;
    private TextField dialog_field_height;
    private ChoiceBox<String> dialog_choiceBox;


    // IMAGE
    private Pixel pixel_buffer;
    private ImageView img_view;
    private WritableImage writable_image;
    private PixelReader pixel_reader;
    private PixelWriter pixel_writer;

    // <!-- CONSTRUCTORS -->
    public Gui(Stage stage, BorderPane border_pane, int width, int height) {
        super(border_pane, width, height);
        this.stage = stage;
        this.STAGE_ORIGINAL_TITLE = this.stage.getTitle();
        this.stage.setTitle(this.STAGE_ORIGINAL_TITLE + this.TITLE_FULL_FX);
        this.root = border_pane;
        this.color_picker = new ColorPicker();
        this.graphic_engine = new GraphicEngine();
        this.pixel_buffer = new Pixel();
        this.pixel_buffer.addObserver(this);

        // MENU
        this.menu_bar = new MenuBar();
        this.menu_bar.setStyle("-fx-background-color : #e74c3c");

        this.file = new Menu("Fichier");
        this.open = new MenuItem("Ouvrir");
        this.save = new MenuItem("Sauvegarder");

        this.menu_create_sheet = new Menu("Nouvelle feuille");
        this.sheet_customized = new MenuItem("Vos propres dimensions");

        this.menu_create_gradation = new Menu("Nouveau dégradé");
        this.gradation_customized = new MenuItem("Vos propres dimensions");

        // For top pane
        this.top_pane = new FlowPane();
        this.top_pane.setStyle("-fx-background-color : #e74c3c");
        this.img_path = new TextField("https://s3-eu-west-1.amazonaws.com/s3.housseniawriting.com/wp-content/uploads/2016/01/Google-Panda.jpg");
        this.button_load_img_from_web = new Button("Charger une image Web");
        this.button_load_img_from_web.setStyle("-fx-background-color : #FFF");

        this.or = new Text(" OU ");
        this.or.setFill(Color.WHITE);

        this.button_load_img_from_local = new Button("Charger une image locale");
        this.button_load_img_from_local.setStyle("-fx-background-color : #FFF");
        this.file_chooser = new FileChooser();

        // For left pane
        this.left_pane = new FlowPane();
        this.left_pane.setStyle("-fx-background-color : #e74c3c");
        this.left_pane.setOrientation(Orientation.VERTICAL);
        this.left_pane.setVgap(5);
        this.left_pane.setColumnHalignment(HPos.CENTER);

        this.create_sheet = new Button("Nouvelle feuille de dessin");
        this.create_sheet.setStyle("-fx-background-color : #FFF");

        this.title_creation_img = new Text("CRÉATION D'UNE IMAGE");
        this.title_creation_img.setFill(Color.WHITE);

        this.label_width = new Label("Largeur : ");
        this.field_width = new TextField("500");
        this.label_width.setTextFill(Color.WHITE);

        this.label_height = new Label("Longueur : ");
        this.field_height = new TextField("500");
        this.label_height.setTextFill(Color.WHITE);

        this.checkbox_random_color_points = new CheckBox("Points de couleur aléatoire");
        this.checkbox_random_color_points.setTextFill(Color.WHITE);

        this.creation_img_pane = new FlowPane();
        this.creation_img_pane.setHgap(10);
        this.creation_img_pane.setAlignment(Pos.CENTER);
        this.cancel_creation_img = new Button("ANNULER");
        this.cancel_creation_img.setStyle("-fx-background-color : #FFF");
        this.continue_creation_img = new Button("CRÉER");
        this.continue_creation_img.setStyle("-fx-background-color : #FFF");

        this.button_hor_gradation = new Button("Dégradé horizontal");
        this.button_hor_gradation.setStyle("-fx-background-color : #FFF");

        this.button_draw_circle = new Button("Nouveau cercle");
        this.button_draw_circle.setStyle("-fx-background-color : #FFF");

        // At center
        this.img_view = new ImageView();
        this.scroll_pane = new ScrollPane(this.img_view);
        this.scroll_pane.setStyle("-fx-background : #FFF");

        // For right pane
        this.right_pane = new FlowPane();
        this.right_pane.setStyle("-fx-background-color : #27ae60");
        this.right_pane.setOrientation(Orientation.VERTICAL);
        this.button_reverse_image = new Button("Inverser l'image");
        this.button_reverse_image.setStyle("-fx-background-color : #FFF");

        // For bot pane
        this.bot_pane = new FlowPane();
        this.bot_pane.setAlignment(Pos.BASELINE_CENTER);
        this.bot_pane.setHgap(20);
        this.bot_pane.setStyle("-fx-background-color : #27ae60");
        this.save_img = new Button("Sauvegarder votre travail");
        this.save_img.setStyle("-fx-background-color : #FFF");
        this.switch_mode = new Button(this.VERSION_WITH_MENU);
        this.switch_mode.setStyle("-fx-background-color : #FFF");

        // Dialogs
        this.dialog_gradation = new Dialog();
        this.dialog_flowpane = new FlowPane(Orientation.VERTICAL);
        this.dialog_gradation.getDialogPane().setContent(this.dialog_flowpane);
        this.dialog_gradation.setTitle("Créer un dégradé");
        this.dialog_label_width = new Label("Largeur :");
        this.dialog_field_width = new TextField("500");
        this.dialog_label_height = new Label("Hauteur :");
        this.dialog_field_height = new TextField("500");
        this.dialog_choiceBox = new ChoiceBox<String>(FXCollections.observableArrayList("Blanc vers noir", "Noir vers blanc", "Polychrome"));
        this.dialog_choiceBox.getSelectionModel().selectFirst();
        this.dialog_flowpane.getChildren().addAll( this.dialog_label_width, this.dialog_field_width,
                                                                    this.dialog_label_height, this.dialog_field_height,
                                                                    this.dialog_choiceBox);
        this.dialog_gradation.getDialogPane().getButtonTypes().addAll(ButtonType.CANCEL, ButtonType.OK);
    }

    public void update(Observable o, Object ob) {
        if(o instanceof Pixel) {
            draw();
        }
    }

    public void draw() {
        this.pixel_writer.setColor(pixel_buffer.x, pixel_buffer.y, pixel_buffer.color);
    }


    // <!-- FILL FUNCTIONS -->
    public void fill() {
        this.fillMenuBar();
        this.fillTopPane();
        this.fillLeftPane();
        this.fillRightPane();
        this.fillBotPane();
        this.fillCreationImgPane();
        this.fillRoot();

        this.disableButtonsBecauseNoLoadedImage(true);

        this.bindUIEvents();
        this.bindGraphicEngineEvents();
    }

    private void fillBotPane() { this.bot_pane.getChildren().addAll(this.save_img, this.switch_mode); }

    private void fillCreationImgPane() { this.creation_img_pane.getChildren().addAll(this.cancel_creation_img, this.continue_creation_img); }

    private void fillLeftPane() {
        this.left_pane.getChildren().addAll(this.create_sheet, this.button_hor_gradation,
                                            this.button_draw_circle
        );
    }

    private void fillMenuBar() {
        this.menu_bar.getMenus().addAll(this.file, this.menu_create_sheet, this.menu_create_gradation);
        this.file.getItems().addAll(this.open, this.save);
        this.menu_create_sheet.getItems().addAll(this.sheet_customized);
        this.menu_create_gradation.getItems().addAll(this.gradation_customized);
    }

    private void fillRightPane() { this.right_pane.getChildren().addAll(this.button_reverse_image); }

    private void fillRoot() {
        this.root.setLeft(this.left_pane);
        this.root.setTop(this.top_pane);
        this.root.setBottom(this.bot_pane);
        this.root.setCenter(this.scroll_pane);
        this.root.setRight(this.right_pane);
    }

    private void fillTopPane() { this.top_pane.getChildren().addAll(this.img_path, this.button_load_img_from_web, this.or, this.button_load_img_from_local); }




    // <!-- HANDLE EVENTS -->

    private void bindGraphicEngineEvents() {
        this.button_reverse_image.setOnAction(button -> {
            this.graphic_engine.restart();
        });
    }

    public void setCustomImg(int width, int height) {
        this.writable_image = new WritableImage(width, height);
        this.pixel_reader = this.writable_image.getPixelReader();
        this.pixel_writer = this.writable_image.getPixelWriter();
        this.graphic_engine.setAttributes((int) this.writable_image.getWidth(),
                (int) this.writable_image.getHeight(),
                this.pixel_reader,
                this.pixel_buffer);
    }

    private void bindUIEvents() {
        // MENU'S EVENTS
        this.sheet_customized.setOnAction(menuItem -> this.displayCreationGui());
        this.gradation_customized.setOnAction(menuItem -> this.dialogHandleEvents());
        //this.open.setOnAction(button ->  { this.graphic_engine.setImg(this.displayFileChooser(0)); this.displayImage(); });
        this.save.setOnAction(button -> this.saveImg(this.displayFileChooser(1)));


        // NOT MENU'S && DIALOGS' EVENTS
        this.button_load_img_from_web.setOnAction(button -> {
            Image img = new Image(this.img_path.getText());
            this.writable_image = new WritableImage(img.getPixelReader(), (int) img.getWidth(), (int) img.getHeight());
            this.pixel_reader = this.writable_image.getPixelReader();
            this.pixel_writer = this.writable_image.getPixelWriter();
            this.graphic_engine.setAttributes((int) this.writable_image.getWidth(),
                    (int) this.writable_image.getHeight(),
                    this.pixel_reader,
                    this.pixel_buffer);

            this.displayImage();
        });

        this.button_load_img_from_local.setOnAction(button -> {
            if(this.displayFileChooser(0) != null) {
                try {
                    WritableImage writable_img = SwingFXUtils.toFXImage(ImageIO.read(this.displayFileChooser(0)), null);
                    this.writable_image = new WritableImage(writable_img.getPixelReader(), (int) writable_img.getWidth(), (int) writable_img.getHeight());
                    this.pixel_reader = this.writable_image.getPixelReader();
                    this.pixel_writer = this.writable_image.getPixelWriter();
                    this.graphic_engine.setAttributes((int) this.writable_image.getWidth(),
                            (int) this.writable_image.getHeight(),
                            this.pixel_reader,
                            this.pixel_buffer);

                    this.displayImage();
                } catch(IOException e) {
                    System.out.println(e);
                }
            }
        });

        this.save_img.setOnAction(button -> this.saveImg(this.displayFileChooser(1)));

        this.create_sheet.setOnAction(button -> this.displayCreationGui());
        this.cancel_creation_img.setOnAction(button -> this.closeCreationGui());
        this.checkbox_random_color_points.setOnAction(chck -> {
            if(this.checkbox_random_color_points.isSelected()) {
                this.color_picker.setDisable(true);
            } else {
                this.color_picker.setDisable(false);
            }
        });
        this.continue_creation_img.setOnAction(button -> {
            this.setCustomImg(Integer.parseInt(this.field_width.getText()), Integer.parseInt(this.field_height.getText()));

            if(!this.checkbox_random_color_points.isSelected()) {
                this.graphic_engine.setBackgroundColor(this.color_picker.getValue());
            } else {
                this.graphic_engine.setBackgroundColorRandom();
            }

            this.closeCreationGui();
            this.displayImage();
        });

        this.switch_mode.setOnAction(button -> this.displayMenuOrButtons());

        this.button_hor_gradation.setOnAction(button -> { this.dialogHandleEvents(); });
        this.button_draw_circle.setOnAction(button -> {
            this.setCustomImg(2000, 2000);
            this.graphic_engine.displayCircle();
        });
    }

    public void saveImg(File file) {
        if(file != null) {
            try {
                String format = file.getName().substring( file.getName().lastIndexOf(".") + 1);
                ImageIO.write(SwingFXUtils.fromFXImage(this.writable_image, null), format, file);
            } catch(IOException e) {
                System.out.println(e);
            }
        }
    }

    private void dialogHandleEvents() {
        this.dialog_gradation.showAndWait().ifPresent( r -> {
            if(r == ButtonType.OK) {
                this.setCustomImg(Integer.parseInt(this.dialog_field_width.getText()), Integer.parseInt(this.dialog_field_height.getText()));
                this.graphic_engine.displayHorGraduation(this.dialog_choiceBox.getValue());
                this.displayImage();
            }
        });
    }



    // <!-- DISPLAY AND CLOSE/HIDE FUNCTIONS -->
    private void closeCreationGui() {
        this.left_pane.getChildren().removeAll(    this.title_creation_img, this.label_width,
                this.field_width, this.label_height,
                this.field_height, this.color_picker, this.checkbox_random_color_points, this.creation_img_pane);

        if(!this.root.getChildren().contains(this.menu_bar)) {
            this.left_pane.getChildren().addAll(this.create_sheet, this.button_hor_gradation);
        }
    }

    private void disableButtonsBecauseNoLoadedImage(boolean b) {
        this.button_reverse_image.setDisable(b);
        this.save_img.setDisable(b);
    }

    private void displayCreationGui() {
        this.left_pane.getChildren().removeAll(this.create_sheet, this.button_hor_gradation);
        this.left_pane.getChildren().addAll(    this.title_creation_img, this.label_width,
                this.field_width, this.label_height,
                this.field_height, this.color_picker, this.checkbox_random_color_points, this.creation_img_pane);
    }

    private File displayFileChooser(int flag) {
        File selected_file = null;
        switch(flag) {
            case 0:
                this.file_chooser.setTitle("Sélectionnez une image");
                selected_file = this.file_chooser.showOpenDialog(this.stage);
                break;
            case 1:
                this.file_chooser.setTitle("Enregistrer votre travail");
                this.file_chooser.getExtensionFilters().addAll(
                        new FileChooser.ExtensionFilter("Image Files", "*.gif", "*.png", "*.jpeg", "*.jpg")
                );
                selected_file = this.file_chooser.showSaveDialog(this.stage);
                break;
        }

        return selected_file;
    }

    public void displayImage() {
        this.img_view.setImage(this.writable_image);

        if(this.writable_image != null || this.writable_image!= null) {
            this.enableButtonsBecauseLoadedImageExists();
        }
    }

    private void displayMenuOrButtons() {
        if(this.root.getChildren().contains(this.menu_bar)) {
            this.root.setTop(this.top_pane);
            this.switch_mode.setText(this.VERSION_WITH_MENU);
            this.left_pane.getChildren().addAll(this.create_sheet, this.button_hor_gradation);
        } else {
            this.root.setTop(this.menu_bar);
            this.switch_mode.setText(this.VERSION_WITH_BUTTONS);
            this.left_pane.getChildren().removeAll(this.create_sheet, this.button_hor_gradation);
        }
    }

    private void enableButtonsBecauseLoadedImageExists() { this.disableButtonsBecauseNoLoadedImage(false); }
}

Launcher.java

import javafx.application.Application;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;

public class Launcher extends Application {

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

    public void start(Stage stage) {
        stage.setWidth(700);
        stage.setHeight(700);
        stage.setMaximized(true);

        Gui gui = new Gui(stage, new BorderPane(), 700, 500);
        gui.fill();

        stage.setScene(gui);
        stage.show();
    }

}

Pixel.java

import javafx.scene.paint.Color;

import java.util.Observable;

public class Pixel extends Observable {
    public int x, y;
    public Color color;

    public Pixel() {

    }

    public Pixel(int x, int y, Color color) {
        this.x = x;
        this.y = y;
        this.color = color;
    }

    public void setAttributes(int x, int y, Color color) {
        this.x = x;
        this.y = y;
        this.color = color;
        this.setChanged();
        this.notifyObservers(this.color);
    }
}