Add a Object to a BranchGroup after the group is added to a Locale or a SimpleUniverse

问题

Consider a simple code:

import java.awt.*;
import javax.media.j3d.*;
import javax.vecmath.Color3f;
import javax.vecmath.*;
import com.sun.j3d.utils.universe.*;
import com.sun.j3d.utils.geometry.*;

public class Main {
  public static void main(final String[] args) {
    final SimpleUniverse universe = new SimpleUniverse();
    final BranchGroup group = new BranchGroup();

    TriangleArray triangle = new TriangleArray(3, TriangleArray.COORDINATES);
    triangle.setCoordinates(0, new Point3f[]{
        new Point3f(-0.3f,     0, -1),
        new Point3f(    0, -0.3f, -1),
        new Point3f(    0,     0, -1),
    });
    group.addChild(new Shape3D(triangle));

    universe.addBranchGraph(group);

    TriangleArray triangle1 = new TriangleArray(3, TriangleArray.COORDINATES);
    triangle1.setCoordinates(0, new Point3f[]{
        new Point3f(0.3f,    0, -1),
        new Point3f(   0, 0.3f, -1),
        new Point3f(   0,    0, -1),
    });
    group.addChild(new Shape3D(triangle1));
  }
}

Before adding group to the universe, I add a triangle triangle to it and it works fine.

After adding the group to the universe, I want to add another triangle triangle1. However, I get the error

Exception in thread "main" javax.media.j3d.RestrictedAccessException: Group: only a BranchGroup node may be added
        at javax.media.j3d.Group.addChild(Group.java:284)
        at Main.<init>(Main.java:34)
        at Main.main(Main.java:11)

So I set the BranchGroup's ALLOW_DETACH capability, remove it from the locale, add the object, then re-add the group to the universe:

// On initialization
group.setCapability(BranchGroup.ALLOW_DETACH);

// ...

// Adding another triangle
group.detach();
group.addChild(new Shape3D(triangle1));
universe.addBranchGraph(group);

However, that appears to be unnecessarily complex. Is there any other, better way to add the Object?

回答1:

Just call BranchGroup.setCapability(Group.ALLOW_CHILDREN_EXTEND) very early and you should be allowed to add new children even after the BranchGroup is added.

来源：https://stackoverflow.com/questions/32423848/add-a-object-to-a-branchgroup-after-the-group-is-added-to-a-locale-or-a-simpleun

标签

java

java-3d