This what I'm doing in an attempt to reuse the model/mesh:

public class Block extends Object3D
{
    public static Object3D MODEL = null;

    public static Object3D getModel()
    {
        if(MODEL == null)
        {
            MODEL = Primitives.getCube(0.5f);
            MODEL.setTexture("box");
            MODEL.setEnvmapped(Object3D.ENVMAP_ENABLED);
            MODEL.setCollisionMode(Object3D.COLLISION_CHECK_OTHERS);
            
            MODEL.build();

            MODEL.rotateY((float) -Math.PI / 4f);
        }

        Object3D newModel = MODEL.cloneObject();
        newModel.shareCompiledData(MODEL);
        newModel.compile();
        
        return newModel;
    }

    public Block()
    {
        super(getModel());
    }

... etc.

Doing these steps improves framerate from ~5 FPS to ~15 FPS. Obviously still not enough to be playable so hopefully I'm just not doing this right or there are other steps that can be taken.

I got frustrated trying to make this work so I ended up prototyping with raw OpenGL. It works much faster with direct calls and now I'm wondering how I can reproduce these results using JPCT. My OpenGL solution uses a single display list (created via GL11.glGenLists(1)) which I reuse repeatedly (GL11.glCallList(that same id)) changing the position per cube of course.

I get up to around 10,000 cubes before performance is impacted, so I know this is possible. I'm sure there's a way to duplicate these results in JPCT with compile or clone, as you've stated above, but all of the combinations I've tried thus far haven't worked.

Long story short... what JPCT calls duplicate the display list functionality of OpenGL?

Is there something I should be doing to prevent rendering objects that are not visible? In the simple demo app I've developed I build a 4x4x4 grid of cube Object3Ds, stacked into a block. That gives me around 250 FPS. If I increase the size of the stack to 16^3 or 4096 Cubes, FPS drops to about 15. I originally was doing this as a physics demo so I went ahead and disabled the physics entirely but that didn't change anything. Profiling the code indicates the bottleneck is rendering.

A lot of the cubes (the ones in the center) are not visible at all, but I imagine they are still being updated/rendered in some way? Is there something I should be doing to prevent this? Unless I'm mistaken I can't merge them into some united list or object, since the physics engine will be altering them individually.

Many apologies if this is obvious or has been covered. I spent about two hours trying to find a solution but nothing has worked yet so I got desperate.

edit:

Some of what I read online indicates that this type of culling is mostly unnecessary. If so, why does my performance drop so much when rendering a lot cubes? I'm not doing anything fancy like turning off back face culling.