Opacity function doesn't support log mapping.
Opacity function doesn't support log mapping.

Since piecewise funciton doesn't log mapping, vtkCompositeControlPointsItem
cannot support showing log-space when in opacity-function mode.

Change-Id: Ib74dddcd347fd49aa2f6bc36cdc9a3daedf6f76c

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