Fix lighting for external rendering environments
Fix lighting for external rendering environments

Account for positional lighting.
Fix calculations for focal point and cutoff.

candy7393/VTK,demarle/VTK,jmerkow/VTK,jmerkow/VTK,gram526/VTK,candy7393/VTK,sumedhasingla/VTK,keithroe/vtkoptix,candy7393/VTK,SimVascular/VTK,keithroe/vtkoptix,mspark93/VTK,sankhesh/VTK,candy7393/VTK,gram526/VTK,gram526/VTK,SimVascular/VTK,sumedhasingla/VTK,sumedhasingla/VTK,gram526/VTK,sankhesh/VTK,mspark93/VTK,demarle/VTK,keithroe/vtkoptix,sankhesh/VTK,jmerkow/VTK,sankhesh/VTK,msmolens/VTK,msmolens/VTK,msmolens/VTK,SimVascular/VTK,demarle/VTK,demarle/VTK,candy7393/VTK,demarle/VTK,demarle/VTK,mspark93/VTK,mspark93/VTK,sankhesh/VTK,msmolens/VTK,msmolens/VTK,jmerkow/VTK,candy7393/VTK,sumedhasingla/VTK,sumedhasingla/VTK,mspark93/VTK,keithroe/vtkoptix,jmerkow/VTK,keithroe/vtkoptix,gram526/VTK,sankhesh/VTK,candy7393/VTK,keithroe/vtkoptix,candy7393/VTK,gram526/VTK,SimVascular/VTK,mspark93/VTK,msmolens/VTK,demarle/VTK,keithroe/vtkoptix,sumedhasingla/VTK,SimVascular/VTK,mspark93/VTK,sumedhasingla/VTK,SimVascular/VTK,jmerkow/VTK,gram526/VTK,jmerkow/VTK,demarle/VTK,gram526/VTK,msmolens/VTK,SimVascular/VTK,mspark93/VTK,keithroe/vtkoptix,sankhesh/VTK,msmolens/VTK,sankhesh/VTK,sumedhasingla/VTK,jmerkow/VTK,SimVascular/VTK