/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2003 Robert Osfield 
 *
 * This library is open source and may be redistributed and/or modified under  
 * the terms of the OpenSceneGraph Public License (OSGPL) version 0.0 or 
 * (at your option) any later version.  The full license is in LICENSE file
 * included with this distribution, and on the openscenegraph.org website.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
 * OpenSceneGraph Public License for more details.
*/

#ifndef OSG_BLENDFUNC
#define OSG_BLENDFUNC 1

#include <osg/StateAttribute>


#ifndef GL_VERSION_1_2
#define GL_CONSTANT_COLOR                 0x8001
#define GL_ONE_MINUS_CONSTANT_COLOR       0x8002
#define GL_CONSTANT_ALPHA                 0x8003
#define GL_ONE_MINUS_CONSTANT_ALPHA       0x8004
#define GL_BLEND_COLOR                    0x8005
#endif



namespace osg {

/** BlendFunc - encapsulates the OpenGL blend/transparency state.*/
class SG_EXPORT BlendFunc : public StateAttribute
{
    public :

        BlendFunc();
        
        BlendFunc(GLenum source, GLenum destination);

        /** Copy constructor using CopyOp to manage deep vs shallow copy.*/
        BlendFunc(const BlendFunc& trans,const CopyOp& copyop=CopyOp::SHALLOW_COPY):
            StateAttribute(trans,copyop),
            _source_factor(trans._source_factor),
            _destination_factor(trans._destination_factor) {}

        META_StateAttribute(osg, BlendFunc,BLENDFUNC);
        
        /** 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(BlendFunc,sa)

            // compare each paramter in turn against the rhs.
            COMPARE_StateAttribute_Parameter(_source_factor)
            COMPARE_StateAttribute_Parameter(_destination_factor)

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

        virtual bool getModeUsage(ModeUsage& usage) const
        {
            usage.usesMode(GL_BLEND);
            return true;
        }

        enum BlendFuncMode {
            DST_ALPHA                = GL_DST_ALPHA,
            DST_COLOR                = GL_DST_COLOR,
            ONE                      = GL_ONE,
            ONE_MINUS_DST_ALPHA      = GL_ONE_MINUS_DST_ALPHA,
            ONE_MINUS_DST_COLOR      = GL_ONE_MINUS_DST_COLOR,
            ONE_MINUS_SRC_ALPHA      = GL_ONE_MINUS_SRC_ALPHA,
            ONE_MINUS_SRC_COLOR      = GL_ONE_MINUS_SRC_COLOR,
            SRC_ALPHA                = GL_SRC_ALPHA,
            SRC_ALPHA_SATURATE       = GL_SRC_ALPHA_SATURATE,
            SRC_COLOR                = GL_SRC_COLOR,
            CONSTANT_ALPHA           = GL_CONSTANT_ALPHA,
            ONE_MINUS_CONSTANT_ALPHA = GL_ONE_MINUS_CONSTANT_ALPHA,
            ZERO                     = GL_ZERO
        };

        inline void setFunction( GLenum source, GLenum destination )
        {
            _source_factor = source;
            _destination_factor = destination;
        }

        void setSource(GLenum source) { _source_factor = source; }
        inline GLenum getSource() const { return _source_factor; }
        
        void setDestination(GLenum destination) { _destination_factor = destination; }
        inline GLenum getDestination() const { return _destination_factor; }

        virtual void apply(State& state) const;

    protected :

        virtual ~BlendFunc();

        GLenum _source_factor;
        GLenum _destination_factor;
};

}

#endif