正多边形与圆相交

Question

I would like to Draw an Regular Polygon inscrit , and I have wrote some code with the usually formula angle = 2*Math.Pi/numside ecc etc.

The Poylgon it's drawn with the circle dynamically with mouse movement in this way:

public void Set_beahvior(Pane DrawPane, BottomPane bottompane )
{
     this.selectedProperty().addListener(new ChangeListener<Boolean>() 

      {

        private final EventHandler<MouseEvent> pressedHandler = (event)    -> {

                cerchio = new MyCircle(event.getX(), event.getY(), 0.0, DrawPane ,bottompane1);
                cerchio.setCenterX(event.getX());
                cerchio.setCenterY(event.getY());
                cerchio.setStrokeType(StrokeType.OUTSIDE);
                cerchio.setStroke(Color.RED);
                cerchio.setFill(Color.TRANSPARENT);
                cerchio.setStrokeWidth(1);
                currentPolygon= new MyPolygon2(DrawPane,bottompane);

                DrawPane.getChildren().addAll(cerchio);
                DrawPane.getChildren().addAll(currentPolygon);              
        };

        private final EventHandler<MouseEvent> draggedHandler = (event) -> {
            cerchio.setRadius((event.getX()-cerchio.getCenterX()));
            currentPolygon.setPolygon(cerchio.getCenterX(), cerchio.getCenterY(), cerchio.getRadius(),cerchio);

        };

        private final EventHandler<MouseEvent> releasedHandler = (event) -> {
            cerchio.setRadius((event.getX()-cerchio.getCenterX()));
            cerchio.setStroke(Color.TRANSPARENT);

        };

        @Override
        public void changed(ObservableValue<? extends Boolean> observable, Boolean oldValue, Boolean newValue) {
            // add/remove event handlers based on toggle state of the button
            if (newValue) {
                DrawPane.addEventHandler(MouseEvent.MOUSE_PRESSED, pressedHandler);
                DrawPane.addEventHandler(MouseEvent.MOUSE_DRAGGED, draggedHandler);
                DrawPane.addEventHandler(MouseEvent.MOUSE_RELEASED, releasedHandler);
            } else {
                DrawPane.removeEventHandler(MouseEvent.MOUSE_PRESSED, pressedHandler);
                DrawPane.removeEventHandler(MouseEvent.MOUSE_DRAGGED, draggedHandler);
                DrawPane.removeEventHandler(MouseEvent.MOUSE_RELEASED, releasedHandler);
            }
        }
  });

And another pieace of code :

     public void setPolygon(Double x, Double y, Double radius, MyCircle circle){

          DoubleProperty raggio = new SimpleDoubleProperty(circle.getRadius());

          double section = 2.0 * Math.PI/Numside;

          this.getPoints().addAll((x + raggio.doubleValue() *  Math.cos(0)), (y + raggio.doubleValue() * Math.sin(0)));
          for(int i=1; i<Numside; i++){ 
               this.getPoints().addAll((x + raggio.doubleValue() * Math.cos(section * i)), (y + raggio.doubleValue() * Math.sin(section * i)));
              }
         } 

THE PROBLEM: I started with 3 side for then I'll write the code for a number of side generic, but All going fine if I increase dynamically the radius of circle (increment the radius -> triangle increase ).

But if I decrease the radius of circle, the polygon doesn't follow the behaviuor of the circle, and I can't understand why, any suggestion please?

PS: please ignore the Doubleproperty and some code written only for a test, I know that if I pass the circle object I don't need the other parameter. At the moment I'm looking at the reason why the polygon does not follow the circumference.

Answer 1

You never clear any of the points from the Polygon . You need to make sure the coordinates in the points list remains twice the number of sides. Furthermore the parameters of setPolygon are not defined well: You pass the same info though the first 3 and the last parameter; also you're using the reference type Double for no obvious reason. The following code improves on the code a bit:

private final int numside;
private final double[] points;

public MyPolygon2(int numside) {
    this.numside = numside;
    this.points = new double[numside * 2];
    double step = 2 * Math.PI / numside;

    for (int i = 0; i < numside; i++) {
        int index = 2 * i;
        double angle = i * step;
        points[index] = Math.cos(angle);
        points[index + 1] = Math.sin(angle);
    }
}

public void setPolygon(double x, double y, double radius) {
    getPoints().clear();
    for (int i = 0; i < points.length;) {
        getPoints().addAll(x + radius * points[i++], y + radius * points[i++]);
    }
}