@Override
    protected Material getMaterial() {
        return material;
    }
Creates a PSSM shadow filter.
More info on the technique at <a href="http://http.developer.nvidia.com/GPUGems3/gpugems3_ch10.html">http://http.developer.nvidia.com/GPUGems3/gpugems3_ch10.html</a>

@param manager the application's asset manager
@param size the size of the rendered shadowmaps (512, 1024, 2048, etcetera)
@param nbSplits the number of shadow maps rendered (More shadow maps mean
    better quality, fewer frames per second.)
jme3-core/src/main/java/com/jme3/shadow/PssmShadowFilter.java