Problem with Polygon intersects

[jpatchak]

Hello,

I am having a problem using intersects method of a class I made that extends Polygon. Basically, I am trying to write code that allows the user to drag these polygons. I create a 1x1 rectangle on a mouse press and look through an array to see if the rectangle intersects the polygon. If it does, then I call the polygon's move class, passing the x and y coordinates while the user is dragging. Problem is that it works the first time, but the each time after that, the intersects method is more and more likely to return false. I even drew the rectangle and I can see that the rectangle is sitting right on top of these shapes. Here is the move method of the polygon:

            public void Move(int x_pos, int y_pos)
            {
 
                for (int myY = 0; myY<this.ypoints.length; myY++)
                    this.ypoints[myY] = this.ypoints[myY] + (y_pos-this.y_position);
                for (int myX=0; myX<this.xpoints.length; myX++)
                    this.xpoints[myX] = this.xpoints[myX] + (x_pos-this.x_position);
                this.x_position = x_pos;
                this.y_position = y_pos;
            }
 

Here is the code in the mouse press that sets the reference to the polygon I want to move:

                    for (PenroseShape p : pShapes)
                    {
                        System.out.println(p.x_position + "," + p.y_position);
 
                        if (p.intersects(r))
                            {
                                Mover = p;
                                OriginalX = p.x_position;
                                OriginalY = p.y_position;
                                dragging=true;
                                System.out.println("Intersection Found");
                            }
                    }
 

And here is the code during the drag that actually moves the polygon (works fine if p.intersects(r) above returns true:

                    if(dragging)
                           {
                              Mover.Move(OriginalX + (e.getX()-StartDragX),OriginalY+(e.getY()-StartDragY));                      
                              System.out.println(Mover.x_position + "," + Mover.y_position);
                              repaint();
                           }
 

I am relatively new to Java and am trying to teach myself, so if I've left out anything that might be critical to anyone being able to help me, please let me know. This has been driving me nuts all night.

Thanks,
Josh

[JosAH]

What happens when you test it the other way around? i.e. r.intersects(p). Also have a look at the contains() method.

kind regards,

Jos

[jpatchak]

r.intersects(p) will not compile - tells me that the intersects method of a rectangular shape can't take p as an argument. I tried contains - created a Point2D at cursor on mouse press and then tested to see if p contains the point and got the same results as with p.intersects(r).

[JosAH]

What is a PenroseShape? Does it extend a Shape or is it another class? If so how is its intersects() method implemented?

kind regards,

Jos

[jpatchak]

The class PenroseShape extends Polygon and has 2 subclasses: kites and dart. Here is the PenroseShape class with its subclasses:

        class PenroseShape extends Polygon
        {
            public int rotation, x_position, y_position;
            public Color pColor;
            public PenroseShape(){}
            public PenroseShape (int x_pos, int y_pos, int rotation)
            {
                this.x_position=x_pos;
                this.y_position=y_pos;
                this.rotation=rotation;
            }
            public void Move(int x_pos, int y_pos)
            {
 
                for (int myY = 0; myY<this.ypoints.length; myY++)
                    this.ypoints[myY] = this.ypoints[myY] + (y_pos-this.y_position);
                for (int myX=0; myX<this.xpoints.length; myX++)
                    this.xpoints[myX] = this.xpoints[myX] + (x_pos-this.x_position);
                this.x_position = x_pos;
                this.y_position = y_pos;
            }
 
        }
        class Kite extends PenroseShape
        {
            public int rotation, x_position, y_position;
            public Color pColor;
 
            public Kite(int x_pos, int y_pos, int rotation)
            {
                pColor = Color.WHITE;
                this.x_position=x_pos;
                this.y_position=y_pos;
                super.addPoint(x_pos+0, y_pos+42);
                super.addPoint(x_pos+125, y_pos+1);
                super.addPoint(x_pos+250, y_pos+42);
                super.addPoint(x_pos+125,  y_pos+214);
            }
 
        }
        class Dart extends PenroseShape
        {
            public int rotation, x_position, y_position;
            public Color pColor;
            public Dart(int x_pos, int y_pos, int rotation)
            {
                pColor = Color.BLACK;
                this.x_position=x_pos;
                this.y_position=y_pos;
                super.addPoint(x_pos+0, y_pos + 173);
                super.addPoint(x_pos+125, y_pos + 1);
                super.addPoint(x_pos+250, y_pos+173);
                super.addPoint(x_pos+125, y_pos+132);
            }
        }
 

[JosAH]

@jpatchak
I don't understand why r.intersects(p) fails to compile; both classes implement the Shape interface so that should work. Can you check that (see my previous replies)? There's something fishy going on ...

kind regards,

Jos

ps. you should also upate the 'bounds' member of the parent class Polygon.

psps. also see the translate() method in the Polygon parent class.

[jpatchak]

I think that the reason that r.intersects(p) won't compile is that the intersects method of Rectangle2D needs type Rectangle2D for the argument - since p is not a Rectangle2D, it won't compile.

Updated bounds in the move method of PenroseShape and no luck.

I'm not getting what I should be doing with the translate method of Polygon here, so if you could give a little bigger clue, that would be helpful.

[jpatchak]

Never mind - I was updating the bounds incorrectly. Once I updated bounds correctly it worked! Thank you for your patience and your expertise!

[JosAH]

@jpatchak
Good; just in case you missed it: there's no need to do all those calculations yourself; the parent class implements the translate() method and the getBounds() method. The fist one translates the entire polygon while the second method produces an updated bounding box.

kind regards,

Jos