public void setGeometryComparator(Bucket bucket, GeometryComparator c) {
        switch (bucket) {
            case Gui:
                guiList = new GeometryList(c);
                break;
            case Opaque:
                opaqueList = new GeometryList(c);
                break;
            case Sky:
                skyList = new GeometryList(c);
                break;
            case Transparent:
                transparentList = new GeometryList(c);
                break;
            case Translucent:
                translucentList = new GeometryList(c);
                break;
            default:
                throw new UnsupportedOperationException("Unknown bucket type: " + bucket);
        }
    }
Sets a different geometry comparator for the specified bucket, one
 of Gui, Opaque, Sky, Transparent, or Translucent.  The GeometryComparators are
 used to sort the accumulated list of geometries before actual rendering
 occurs.

 <p>The most significant comparator is the one for the transparent
 bucket since there is no correct way to sort the transparent bucket
 that will handle all geometries all the time.  In certain cases, the
 application may know the best way to sort and now has the option of
 configuring a specific implementation.</p>

 <p>The default comparators are:</p>
 <ul>
 <li>Bucket.Opaque: {@link com.jme3.renderer.queue.OpaqueComparator} which sorts
                    by material first and front to back within the same material.
 <li>Bucket.Transparent: {@link com.jme3.renderer.queue.TransparentComparator} which
                    sorts purely back to front by leading bounding edge with no material sort.
 <li>Bucket.Translucent: {@link com.jme3.renderer.queue.TransparentComparator} which
                    sorts purely back to front by leading bounding edge with no material sort. this bucket is rendered after post processors.
 <li>Bucket.Sky: {@link com.jme3.renderer.queue.NullComparator} which does no sorting
                    at all.
 <li>Bucket.Gui: {@link com.jme3.renderer.queue.GuiComparator} sorts geometries back to
                    front based on their Z values.
 </ul>

@param bucket which Bucket to modify (not null)
@param c the comparator to use (alias created)
jme3-core/src/main/java/com/jme3/renderer/queue/RenderQueue.java