@Override
    protected void preFrame(float tpf) {
        shadowRenderer.preFrame(tpf);
        if( instanceRendering ) {
            material.setMatrix4("ViewProjectionMatrixInverseRight", rightCamera.getViewProjectionMatrix().invert());
            Matrix4f m = rightCamera.getViewProjectionMatrix();
            material.setVector4("ViewProjectionMatrixRow2Right", temp4f2.set(m.m20, m.m21, m.m22, m.m23));
        }
        material.setMatrix4("ViewProjectionMatrixInverse", viewPort.getCamera().getViewProjectionMatrix().invert());
        Matrix4f m = viewPort.getCamera().getViewProjectionMatrix();
        material.setVector4("ViewProjectionMatrixRow2", temp4f.set(m.m20, m.m21, m.m22, m.m23));
    }
Create a new instanced version of the {@link DirectionalLightShadowFilterVR directional light shadow filter}.
@param application the application that this filter is attached to.
@param camera
@param shadowMapSize the size of the rendered shadowmaps (512, 1024, 2048, etcetera)
@param nbSplits the number of shadow maps rendered (More shadow maps yield
    better quality, fewer frames per second.)
@param instancedRendering <code>true</code> if this filter has to use instance rendering and <code>false</code> otherwise.
@param rightCamera the camera used as right eye in stereo rendering mode.
jme3-vr/src/main/java/com/jme3/shadow/InstancedDirectionalShadowFilter.java