void createWhiteLines() {
        Mesh lineMesh = new Mesh();
        lineMesh.setMode(Mesh.Mode.Lines);
        float[] corners = new float[]{
            -1f, -1f, 0f,
            -1f, 1f, 0f,
            1f, 1f, 0f,
            1f, -1f, 0f
        };
        lineMesh.setBuffer(VertexBuffer.Type.Position, 3, corners);
        short[] indices = new short[]{0, 1, 2, 3};
        lineMesh.setBuffer(VertexBuffer.Type.Index, 2, indices);
        lineMesh.updateBound();
        Geometry whiteLines = new Geometry("white lines", lineMesh);
        Material white = assetManager.loadMaterial("Common/Materials/WhiteColor.j3m");
        whiteLines.setMaterial(white);
        whiteLines.move(0f, 0f, 1f);
        rootNode.attachChild(whiteLines);
    }
Attach a pair of parallel white lines in the z=1 plane.
jme3-core/src/test/java/com/jme3/scene/PhantomTrianglesTest.java