Fixed gradient opacity computation
Fixed gradient opacity computation

Change-Id: Ia9355328e5919ba8db09f84baaeff8ad4e3c5dda

ashray/VTK-EVM,sankhesh/VTK,gram526/VTK,candy7393/VTK,candy7393/VTK,hendradarwin/VTK,keithroe/vtkoptix,hendradarwin/VTK,mspark93/VTK,sumedhasingla/VTK,demarle/VTK,keithroe/vtkoptix,sumedhasingla/VTK,SimVascular/VTK,demarle/VTK,hendradarwin/VTK,ashray/VTK-EVM,mspark93/VTK,demarle/VTK,johnkit/vtk-dev,jmerkow/VTK,sankhesh/VTK,mspark93/VTK,candy7393/VTK,mspark93/VTK,johnkit/vtk-dev,jmerkow/VTK,SimVascular/VTK,SimVascular/VTK,ashray/VTK-EVM,candy7393/VTK,msmolens/VTK,sumedhasingla/VTK,gram526/VTK,jmerkow/VTK,sankhesh/VTK,msmolens/VTK,keithroe/vtkoptix,msmolens/VTK,johnkit/vtk-dev,ashray/VTK-EVM,gram526/VTK,sumedhasingla/VTK,sankhesh/VTK,johnkit/vtk-dev,SimVascular/VTK,ashray/VTK-EVM,sankhesh/VTK,johnkit/vtk-dev,sumedhasingla/VTK,gram526/VTK,candy7393/VTK,gram526/VTK,johnkit/vtk-dev,ashray/VTK-EVM,mspark93/VTK,hendradarwin/VTK,ashray/VTK-EVM,msmolens/VTK,hendradarwin/VTK,demarle/VTK,keithroe/vtkoptix,gram526/VTK,jmerkow/VTK,sankhesh/VTK,gram526/VTK,jmerkow/VTK,mspark93/VTK,jmerkow/VTK,gram526/VTK,msmolens/VTK,keithroe/vtkoptix,candy7393/VTK,msmolens/VTK,sumedhasingla/VTK,jmerkow/VTK,mspark93/VTK,jmerkow/VTK,SimVascular/VTK,demarle/VTK,hendradarwin/VTK,msmolens/VTK,ashray/VTK-EVM,keithroe/vtkoptix,keithroe/vtkoptix,hendradarwin/VTK,candy7393/VTK,SimVascular/VTK,demarle/VTK,SimVascular/VTK,johnkit/vtk-dev,SimVascular/VTK,keithroe/vtkoptix,sankhesh/VTK,sumedhasingla/VTK,sumedhasingla/VTK,msmolens/VTK,mspark93/VTK,demarle/VTK,candy7393/VTK,demarle/VTK,sankhesh/VTK