Added extra constructor to make it more convinient to create AlphaFunc.
Added extra constructor to make it more convinient to create AlphaFunc.


artoolkit/osg,artoolkit/osg,artoolkit/osg,tomasthoresen/osg,openscenegraph/osg,jtorresfabra/osg,tomasthoresen/osg,openscenegraph/osg,marchelbling/osg,scrawl/osg,openscenegraph/osg,scrawl/osg,tomasthoresen/osg,jtorresfabra/osg,tomasthoresen/osg,scrawl/osg,openscenegraph/osg,marchelbling/osg,scrawl/osg,marchelbling/osg,artoolkit/osg,marchelbling/osg,jtorresfabra/osg,jtorresfabra/osg