如何在Piccolo2D中使用多个图层？ [英] How to use multiple layers in Piccolo2D?

问题描述

我想要有一张照片在另一张上面，并且想要利用。

在您的情况下，您缺少从 PCamera 的 PRoot code>。这是一个简单的修复：

 私人PCamera相机=新PCamera（）; {
 PRoot root = new PRoot（）; 
 root.addChild（camera）; 
 camera.addLayer（layer1）; 
 camera.addLayer（layer2）; 
 camera.addLayer（layer3）; 
} 
  

结果如下：

仅供参考这是从 PUtil.createBasicScenegraph（）创建一个基本相机的副本。

  public static PCamera createBasicScenegraph（）{
 final PRoot root = new PRoot（）; 
最终PLayer图层=新PLayer（）; 
最终PCamera相机=新PCamera（）; 
 
 root.addChild（camera）; 
 root.addChild（layer）; 
 camera.addLayer（layer）; 
 
返回相机; 
} 
  

I want t have some picture above another one and want to utilize PCamera's addLayer() method.

Is this possible?

The following code throws NullPointerException. What's wrong with it?

package test.piccolo;

import java.awt.Color;

import edu.umd.cs.piccolo.PCamera;
import edu.umd.cs.piccolo.PLayer;
import edu.umd.cs.piccolo.nodes.PPath;
import edu.umd.cs.piccolox.PFrame;

public class Try_Cameras_01 {
    @SuppressWarnings("serial")
    public static void main(String[] args) {
        new PFrame() {



            private PLayer layer1 = new PLayer();

            private PLayer layer2 = new PLayer();

            private PLayer layer3 = new PLayer();

            private PCamera camera = new PCamera();
            {
                camera.addLayer(layer1);
                camera.addLayer(layer2);
                camera.addLayer(layer3);
            }


            @Override
            public void initialize() {

                getCanvas().setCamera(camera);

                PPath redRectangle = PPath.createRectangle(0, 0, 100, 100);
                redRectangle.setStrokePaint(Color.black);
                redRectangle.setPaint(Color.red);

                PPath greenRectangle = PPath.createRectangle(20, 20, 100, 100);
                greenRectangle.setStrokePaint(Color.black);
                greenRectangle.setPaint(Color.green);

                PPath blueRectangle = PPath.createRectangle(40, 40, 100, 100);
                blueRectangle.setStrokePaint(Color.black);
                blueRectangle.setPaint(Color.blue);

                layer1.addChild(redRectangle);
                layer2.addChild(greenRectangle);
                layer3.addChild(blueRectangle);


            }
        };
    }
}

解决方案

The problem is that when you set up a new camera it has no associated root. As a result, PCanvas.getRoot() returns null and there an NPE in one of the painting methods. Here is a basic Piccolo2D runtime structure:

Read more in Piccolo2D Patterns.

In your case you're missing a link to PRoot from a PCamera. Here is a simple fix:

private PCamera camera = new PCamera(); {
    PRoot root = new PRoot();
    root.addChild(camera);
    camera.addLayer(layer1);
    camera.addLayer(layer2);
    camera.addLayer(layer3);
}

That results in:

For reference here is a copy from PUtil.createBasicScenegraph() that creates a basic camera.

public static PCamera createBasicScenegraph() {
    final PRoot root = new PRoot();
    final PLayer layer = new PLayer();
    final PCamera camera = new PCamera();

    root.addChild(camera);
    root.addChild(layer);
    camera.addLayer(layer);

    return camera;
}

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