@Override
    protected void initFrustumCam() {
        //nothing to do
    }
Creates a DirectionalLight shadow renderer. More info on the technique at <a
href="https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch10.html">https://developer.nvidia.com/gpugems/GPUGems3/gpugems3_ch10.html</a>

@param assetManager the application's asset manager
@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 fps.)
jme3-core/src/main/java/com/jme3/shadow/DirectionalLightShadowRenderer.java