import static java.lang.Math.PI;
import static java.lang.Math.cos;
import static java.lang.Math.sin;

import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.stage.Stage;

public class N_gon extends Application {
    public void start(Stage stage) {
        stage.setTitle("正多角形");

        final Canvas canvas = new Canvas(220, 220);
        GraphicsContext gc = canvas.getGraphicsContext2D();

        int np = 7;
        int sc = 100;

        int i;
        double theta1, theta2;
        for(i = 0; i < np; i++) {
            // 単位 ラジアン
            theta1 = PI * 2 * i / np;        // 360 * i / n度
            theta2 = PI * 2 * (i + 1) / np;  // 360 * (i + 1) / n度
            gc.strokeLine((int)(sc * (1.1 + cos(theta1))),
                    (int)(sc * (1.1 + sin(theta1))),
                    (int)(sc * (1.1 + cos(theta2))),
                    (int)(sc * (1.1 + sin(theta2))));
        }

        Group root = new Group();
        root.getChildren().addAll(canvas);
        Scene scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
    }

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