Rotate line segment with Button

Question

I have a line which has points (x1,y1) and (x2,y2). I wanted to attach a Button to it, it should align with the line by rotating based on the line segment points. I need some help in calculating the rotation angle for the Button.

Answer 1

You can use the Math.atan2(dy, dx) to get the angle theta from the conversion of rectangular coordinates (x, y) to polar coordinates (r, theta). Later use it to convert it to degrees.

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.StackPane;
import javafx.scene.shape.Line;
import javafx.stage.Stage;

public class Main extends Application {

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

    @Override
    public void start(Stage primaryStage) throws Exception {
        double startX = 100;
        double endX = 250;
        double startY = 150;
        double endY = 250;

        Line line = new Line(startX, startY, endX, endY);
        Button button = new Button("Button");

        double rad  = Math.atan2(endY - startY, endX - startX);
        double degree = rad * 180/Math.PI;
        button.setRotate(degree);

        StackPane box = new StackPane(line, button);

        Scene scene = new Scene(box, 500, 500);
        primaryStage.setScene(scene);
        primaryStage.show();
    }
}

OutPut