//C++ header - Open Scene Graph - Copyright (C) 1998-2001 Robert Osfield
//Distributed under the terms of the GNU Library General Public License (LGPL)
//as published by the Free Software Foundation.

#ifndef OSG_ALPHAFUNC
#define OSG_ALPHAFUNC 1

#include <osg/StateAttribute>
#include <osg/StateSet>

namespace osg {

/** Encapsulate OpenGL glAlphaFunc.
*/     
class SG_EXPORT AlphaFunc : public StateAttribute
{
    public :
    
    
        AlphaFunc();
        
        /** Copy constructor using CopyOp to manage deep vs shallow copy.*/
        AlphaFunc(const AlphaFunc& af,const CopyOp& copyop=CopyOp::SHALLOW_COPY):
            StateAttribute(af,copyop),
            _comparisonFunc(af._comparisonFunc),
            _referenceValue(af._referenceValue) {}
        
        META_StateAttribute(osg, AlphaFunc,ALPHAFUNC);
        
        /** return -1 if *this < *rhs, 0 if *this==*rhs, 1 if *this>*rhs.*/
        virtual int compare(const StateAttribute& sa) const
        {
            // check the types are equal and then create the rhs variable
            // used by the COMPARE_StateAttribute_Paramter macro's below.
            COMPARE_StateAttribute_Types(AlphaFunc,sa)

            // compare each paramter in turn against the rhs.
            COMPARE_StateAttribute_Parameter(_comparisonFunc)
            COMPARE_StateAttribute_Parameter(_referenceValue)

            return 0; // passed all the above comparison macro's, must be equal.
        }

        virtual void setStateSetModes(StateSet& ds,const GLModeValue value) const
        {
            ds.setMode(GL_ALPHA_TEST,value);
        }

        enum ComparisonFunction {
            NEVER = GL_NEVER,
            LESS = GL_LESS,
            EQUAL = GL_EQUAL,
            LEQUAL = GL_LEQUAL,
            GREATER = GL_GREATER,
            NOTEQUAL = GL_NOTEQUAL,
            GEQUAL = GL_GEQUAL,
            ALWAYS = GL_ALWAYS
        };

        inline void setFunction(const ComparisonFunction func,const float ref)
        {
            _comparisonFunc = func;
            _referenceValue = ref;
        }
        
        inline const ComparisonFunction getFunction() const { return _comparisonFunc; }
        
        inline const float getReferenceValue() const { return _referenceValue; }
        
        virtual void apply(State& state) const;

    protected:
    
        virtual ~AlphaFunc();

        ComparisonFunction _comparisonFunc;
        float _referenceValue;

};

}

#endif