javapiccolo

SimpleEllipseExample just does not work in Piccolo2D?


What piccolo example below should actually do? I draws nothing for me. And paint method never called:

package test.piccolo;

import java.awt.Graphics2D;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Rectangle2D;

import edu.umd.cs.piccolo.PNode;
import edu.umd.cs.piccolo.nodes.PText;
import edu.umd.cs.piccolo.util.PPaintContext;
import edu.umd.cs.piccolox.PFrame;

public class SimpleEllipseNode extends PNode {
    private Ellipse2D ellipse;

    // This nodes uses an internal Ellipse2D to define its shape.
    public Ellipse2D getEllipse() {
        if (ellipse == null)
            ellipse = new Ellipse2D.Double();
        return ellipse;
    }

    // This method is important to override so that the geometry of
    // the ellipse stays consistent with the bounds geometry.
    public boolean setBounds(double x, double y, double width, double height) {
        if (super.setBounds(x, y, width, height)) {
            ellipse.setFrame(x, y, width, height);
            return true;
        }
        return false;
    }

    // Non rectangular subclasses need to override this method so
    // that they will be picked correctly and will receive the
    // correct mouse events.
    public boolean intersects(Rectangle2D aBounds) {
        return getEllipse().intersects(aBounds);
    }

    // Nodes that override the visual representation of their super
    // class need to override a paint method.
    public void paint(PPaintContext aPaintContext) {
        Graphics2D g2 = aPaintContext.getGraphics();
        g2.setPaint(getPaint());
        g2.fill(getEllipse());
    }

    public static void main(String[] args) {

        PFrame frame = new PFrame() {

            @Override
            public void initialize() {

                PNode aNode = new SimpleEllipseNode();
                //PNode aNode = new PText("Hello World!");

                // Add the node to the canvas layer so that it
                // will be displayed on the screen.
                getCanvas().getLayer().addChild(aNode);
            }

        };

    }
}

Solution

  • The ellipse is not painted probably because the bounds of SimpleEllipseNode are empty. Add these lines to initialize() :

    aNode.setPaint(Color.RED);
    aNode.setBounds(0, 0, 100, 100);
    

    And it should paint a red ellipse. There is an NPE in setBounds() since the ellipse is not initialized yet. This can be fixed by adding getEllipse(); as a first line in setBounds().

    Not sure what is the reason behind overriding paint() and setBounds(), as usually you can get away easily by using compositional nodes. For example:

    import java.awt.Color;
    import edu.umd.cs.piccolo.nodes.PPath;
    import edu.umd.cs.piccolox.PFrame;
    
    public class SimpleEllipseNode {
        public static void main(final String[] args) {
            PFrame frame = new PFrame() {
                @Override
                public void initialize() {
                    final PPath circle = PPath.createEllipse(0, 0, 100, 100);
                    circle.setPaint(Color.RED);
                    getCanvas().getLayer().addChild(circle);
                }
            };
        }
    }