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Friday, 13 January 2017

Chapter 18 Exercise 37, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

18.37 (Hilbert curve)
The Hilbert curve, first described by German mathematician David Hilbert in 1891,
is a space-filling curve that visits every point in a square grid with a
size of 22, 44, 88, 1616, or any other power of 2.
Write a program that displays a Hilbert curve for the specified order


import javafx.application.Application;
import javafx.collections.ObservableList;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.input.KeyCode;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Polyline;
import javafx.stage.Stage;

public class Exercise_37 extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception {

        HilbertCurvePane pane = new HilbertCurvePane();
        primaryStage.setScene(new Scene(pane));
        primaryStage.show();
    }

    class HilbertCurvePane extends BorderPane {

        private final int UP = 0;
        private final int RIGHT = 1;
        private final int DOWN = 2;
        private final int LEFT = 3;

        Label lblOrder = new Label("Enter Order:");
        TextField tfOrder = new TextField("0");
        Polyline polyline = new Polyline();
        Pane pane = new Pane(polyline);

        private double x1;
        private double y1;
        double length = 10;

        int order;

        HilbertCurvePane() {
            setMinSize(400, 400);

            HBox hBox = new HBox(10, lblOrder, tfOrder);
            hBox.setAlignment(Pos.BASELINE_CENTER);
            hBox.setPadding(new Insets(10));

            tfOrder.setPrefColumnCount(4);
            tfOrder.setAlignment(Pos.BASELINE_RIGHT);
            tfOrder.setOnKeyPressed(e-> {

                if (e.getCode() == KeyCode.ENTER) {
                    try {
                        order = Integer.parseInt(tfOrder.getText());
                    } catch (NumberFormatException ex) {
                        order = 0;
                        tfOrder.setText("0");
                    }
                    draw();
                } else if (e.getCode() == KeyCode.UP) {
                    order = Integer.parseInt(tfOrder.getText()) + 1;
                    tfOrder.setText(order + "");
                    draw();
                }else if (e.getCode() == KeyCode.DOWN) {
                    order = Math.max(Integer.parseInt(tfOrder.getText()) - 1, 0);
                    tfOrder.setText(order + "");
                    draw();
                }
            });
            setBottom(hBox);

            setCenter(pane);
        }

        private void draw() {
            if (order == 0) return;

            polyline.getPoints().clear();
            length = 50 / order;
            x1 = Math.min(getWidth(), getHeight()) - 50;
            y1 = x1;
            polyline.getPoints().addAll(x1, y1);
            draw(order, DOWN);
        }

        private void draw(int order, int direction) {

            if (order == 1) {
                switch (direction) {
                    case UP:
                        move(DOWN);
                        move(RIGHT);
                        move(UP);
                        break;
                    case RIGHT:
                        move(LEFT);
                        move(UP);
                        move(RIGHT);
                        break;
                    case DOWN:
                        move(UP);
                        move(LEFT);
                        move(DOWN);
                        break;
                    case LEFT:
                        move(RIGHT);
                        move(DOWN);
                        move(LEFT);
                        break;
                }

            } else if (order > 1){
                    switch (direction) {
                        case UP:
                            draw(order - 1, LEFT);
                            move(DOWN);
                            draw(order - 1, UP);
                            move(RIGHT);
                            draw(order - 1, UP);
                            move(UP);
                            draw(order - 1, RIGHT);
                            break;
                        case RIGHT:
                            draw(order - 1, DOWN);
                            move(LEFT);
                            draw(order - 1, RIGHT);
                            move(UP);
                            draw(order - 1, RIGHT);
                            move(RIGHT);
                            draw(order - 1, UP);
                            break;
                        case DOWN:
                            draw(order - 1, RIGHT);
                            move(UP);
                            draw(order - 1, DOWN);
                            move(LEFT);
                            draw(order - 1, DOWN);
                            move(DOWN);
                            draw(order - 1, LEFT);
                            break;
                        case LEFT:
                            draw(order - 1, UP);
                            move(RIGHT);
                            draw(order - 1, LEFT);
                            move(DOWN);
                            draw(order - 1, LEFT);
                            move(LEFT);
                            draw(order - 1, DOWN);
                            break;
                    }
                }
        }

        private void move(int direction) {
            ObservableList<Double> list = polyline.getPoints();
            switch (direction) {
                case UP:
                    list.addAll(x1, y1 -= length);
                    break;
                case RIGHT:
                    list.addAll(x1 += length, y1);
                    break;
                case DOWN:
                    list.addAll(x1, y1 += length);
                    break;
                case LEFT:
                    list.addAll(x1 -= length, y1);
                    break;
            }

        }
    }

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

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