JavaFX - 如何在JavaFX画布上绘制

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

public class Main extends Application {  
  public static void main(String[] args) {
    Application.launch(args);
  }

  @Override
  public void start(Stage stage) {
    Canvas canvas = new Canvas(300, 100);
    
    GraphicsContext gc = canvas.getGraphicsContext2D();

    gc.setLineWidth(2.0);
    gc.setFill(Color.RED);

    gc.strokeRoundRect(10, 10, 50, 50, 10, 10);
    
    gc.fillOval(70, 10, 50, 20);
  
    gc.strokeText("Hello Canvas", 150, 20);

    Pane root = new Pane();
    root.getChildren().add(canvas);
    Scene scene = new Scene(root);
    stage.setScene(scene);
    stage.setTitle("");
    stage.show();
  }
}