Sierpinski Triangle

package sierpinskiTriangle;

import javafx.application.Application;
import javafx.geometry.Point2D;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Polygon;
import javafx.stage.Stage;

public class SierpinskiTriangle extends Application {
	
	/**
	 * Main method
	 * @param args
	 */
	public static void main(String[] args) {
		Application.launch(args);
	}

	@Override // Override the start method in the Application class
	public void start(Stage primaryStage) throws Exception {
		SierpinskiTrianglePane pane = new SierpinskiTrianglePane();
		TextField tfOrder = new TextField();
		tfOrder.setOnAction(e -> {
			pane.setOrder(Integer.parseInt(tfOrder.getText()));
		});
		tfOrder.setPrefColumnCount(4);
		tfOrder.setAlignment(Pos.BOTTOM_RIGHT);
		
		// Pane to hold label and text field
		HBox hBox = new HBox(10);
		hBox.getChildren().addAll(new Label("Enter an order: "), tfOrder);
		hBox.setAlignment(Pos.CENTER);
		
		BorderPane borderPane = new BorderPane();
		borderPane.setCenter(pane);
		borderPane.setBottom(hBox);
		
		// Create a scene and palce it in the stage
		Scene scene = new Scene(borderPane, 200, 210);
		primaryStage.setTitle("Koch Snowflake Fractal");
		primaryStage.setScene(scene);
		primaryStage.show();
		
		// Add listeners
		scene.widthProperty().addListener(ov -> pane.paint());
		scene.heightProperty().addListener(ov -> pane.paint());
	}
	
	/**
	 * Pane for displaying Koch snowflake fractals
	 */
	static class SierpinskiTrianglePane extends Pane {
		private int order = 0;
		
		/** Default constructor */
		SierpinskiTrianglePane() {
		}
		
		/** Set a new order */
		public void setOrder(int order) {
			this.order = order;
			paint();
		}
		
		protected void paint() {
			Point2D p1 = new Point2D(getWidth() / 2, 10);
			Point2D p2 = new Point2D(10, getHeight() - 10);
			Point2D p3 = new Point2D(getWidth() - 10, getHeight() - 10);
			
			this.getChildren().clear();
			
			displayTriangles(order, p1, p2, p3);
		}
		
		private void displayTriangles(int order, Point2D p1, Point2D p2, Point2D p3) {
			if (order == 0) {
				// Draw a triangle to connect three points
				Polygon triangle = new Polygon();
				triangle.getPoints().addAll(p1.getX(), p1.getY(), p2.getX(), p2.getY(), p3.getX(), p3.getY());
				triangle.setStroke(Color.LIMEGREEN);
				triangle.setFill(Color.LAVENDER);
				
				this.getChildren().add(triangle);
			}
			else {
				// Get the midpoint on each edge in the triangle
				Point2D p12 = p1.midpoint(p2);
				Point2D p23 = p2.midpoint(p3);
				Point2D p31 = p3.midpoint(p1);
				
				// Recursively display three triangles
				displayTriangles(order - 1, p1, p12, p31);
				displayTriangles(order - 1, p12, p2, p23);
				displayTriangles(order - 1, p31, p23, p3);
			}	
		}
	}
}