Por que minha tela não é mostrada no aplicativo JavaFX?

Meu professor na universidade deu esta tarefa para iniciar um novo tópico em aula. Apenas uma GUI simples que supostamente mostra um gráfico. 3 Arquivos foram elaborados pelo nosso Prof:

Tela de Função

package Aufgabe1.jfx;

import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.paint.Color;

final class FunctionCanvas extends Canvas
{
    private double c1 = 1, d1 = 0, c2 = 1, d2 = 0;

    void setFunctionParameters(double c1, double d1, double c2, double d2)
    {
        this.c1 = c1;
        this.d1 = d1;
        this.c2 = c2;
        this.d2 = d2;
    }

    FunctionCanvas() {}

    private static final float v = 244f / 255;
    private static final Color backGroundColor = Color.color(0, 0, 0);
    private static final int yOffset = 20;

    void drawFunctionCurve() {
        GraphicsContext gc = getGraphicsContext2D();
        //float v = 244f / 255;
        gc.setFill(backGroundColor);
        gc.fillRect(0, 0, getWidth(), getHeight());

        double h = this.getHeight() - 2 * yOffset;
        int xOffset = 40;
        double w = this.getWidth() - 2 * xOffset;
        double yZero = yOffset + h / 2;
        gc.setFill(Color.BLACK);
        gc.fillText("f(x)", xOffset - 30, yOffset);
        gc.fillText("0", xOffset - 25, yZero + 5);
        gc.fillText("2\u03c0", xOffset + w - 5, yZero - 5);
        gc.setLineWidth(1.0);
        gc.setStroke(Color.GRAY);
        gc.strokeLine(xOffset, yOffset, xOffset, yOffset + h);
        gc.strokeLine(xOffset, yZero, xOffset + w, yZero);
        gc.setLineWidth(1.5);
        gc.setStroke(Color.INDIANRED);
        for (int x = 0; x < w; x++) {
            int y = (int) ((h / 2) * sinCosFunc(x * 2 * Math.PI / w));
            gc.strokeLine(xOffset + x, yZero - y, xOffset + x, yZero - y);
        }
    }

    private double sinCosFunc(double x)
    {
        return Math.sin(c1 * x + d1) * Math.cos(c2 * x + d2);
    }
}

CurvaFuncional

package Aufgabe1.jfx;

import javafx.application.Application;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.layout.AnchorPane;
import javafx.stage.Stage;

public class FunctionCurve extends Application {
    public FunctionCurve() { }
    @Override
    public void start(Stage stage) throws Exception {
        int width = 670;
        int height = 520;
        //Written by me
        FXMLLoader loader = new FXMLLoader(getClass().getResource("1gui.fxml"));
        Parent root = loader.load();
        Scene scene = new Scene(root, width, height);
        stage.setTitle(this.getClass().getSimpleName());
        stage.setScene(scene);
        stage.centerOnScreen();
        stage.show();

    }
}

Principal

package Aufgabe1.jfx;

final class Main
{
    private Main() {}

    public static void main(String[] args)
    {
        javafx.application.Application.launch(FunctionCurve.class, args);
    }
}

Eu já criei o arquivo FXML e escrevi o controlador com o melhor de minhas habilidades:

FXML

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.geometry.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>

<SplitPane dividerPositions="0.08892617449664429" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" orientation="VERTICAL" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/17.0.2-ea" xmlns:fx="http://javafx.com/fxml/1" fx:controller="Aufgabe1.jfx.Controller">
  <items>
    <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="100.0" prefWidth="160.0">
         <children>
            <HBox prefHeight="48.0" prefWidth="597.0">
               <children>
                  <Label prefHeight="25.0" prefWidth="25.0" text="c1">
                     <padding>
                        <Insets left="5.0" right="5.0" />
                     </padding>
                  </Label>
                  <Spinner editable="true" prefHeight="10.0" prefWidth="50.0" />
                  <Label prefHeight="25.0" prefWidth="25.0" text="d1">
                     <padding>
                        <Insets left="5.0" right="5.0" />
                     </padding>
                  </Label>
                  <Spinner editable="true" prefHeight="10.0" prefWidth="50.0" />
                  <Label prefHeight="25.0" prefWidth="25.0" text="c2">
                     <padding>
                        <Insets left="5.0" right="5.0" />
                     </padding>
                  </Label>
                  <Spinner editable="true" prefHeight="10.0" prefWidth="50.0" />
                  <Label prefHeight="25.0" prefWidth="25.0" text="d2">
                     <padding>
                        <Insets left="5.0" right="5.0" />
                     </padding>
                  </Label>
                  <Spinner editable="true" prefHeight="10.0" prefWidth="50.0" />
                  <Button mnemonicParsing="false" text="Button">
                     <HBox.margin>
                        <Insets left="5.0" right="5.0" />
                     </HBox.margin>
                  </Button>
                  <Button mnemonicParsing="false" text="reset">
                     <HBox.margin>
                        <Insets left="5.0" right="5.0" />
                     </HBox.margin>
                  </Button>
               </children>
            </HBox>
         </children></AnchorPane>
      <AnchorPane fx:id="_canvas" prefHeight="600.0" prefWidth="400.0" />
  </items>
</SplitPane>

Controlador

package Aufgabe1.jfx;

import javafx.fxml.FXML;
import javafx.scene.layout.AnchorPane;

public class Controller {

    @FXML
    private AnchorPane _canvas ;

    // called by the FXML loader after the labels declared above are injected:
    public void initialize() {
        FunctionCanvas c = new FunctionCanvas();
        _canvas.setPrefWidth(400);
        _canvas.setPrefHeight(300);
        _canvas.getChildren().add(c);
        c.drawFunctionCurve();

    }
}

Tentei praticamente todas as soluções que encontrei na web, mas sempre que executo o aplicativo a tela com o gráfico não aparece. Estou trabalhando com o IntelliJ IDEA, se isso importa ...