OpenSceneGraph/include/osg/BlendEquation

/* -*-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_BLENDEQUATION
#define OSG_BLENDEQUATION 1

#include <osg/StateAttribute>

#ifndef GL_VERSION_1_2
/* Logic Ops */
#define GL_MIN					0x8007
#define GL_MAX					0x8008
#define GL_FUNC_ADD				0x8006
#define GL_FUNC_SUBTRACT			0x800A
#define GL_FUNC_REVERSE_SUBTRACT		0x800B
#define GL_ALPHA_MIN_SGIX			0x8320
#define GL_ALPHA_MAX_SGIX			0x8321
#define GL_LOGIC_OP				0x0BF1
#endif



namespace osg {

/** Encapsulates OpenGL BlendEquation state. */
class SG_EXPORT BlendEquation : public StateAttribute
{
    public :

        BlendEquation();
        
        BlendEquation(GLenum equation);

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

        META_StateAttribute(osg, BlendEquation,BLENDEQUATION);
        
        /** Return -1 if *this < *rhs, 0 if *this==*rhs, 1 if *this>*rhs. */
        virtual int compare(const StateAttribute& sa) const
        {
            // Check for equal types, then create the rhs variable
            // used by the COMPARE_StateAttribute_Paramter macros below.
            COMPARE_StateAttribute_Types(BlendEquation,sa)

            // Compare each parameter in turn against the rhs.
            COMPARE_StateAttribute_Parameter(_equation)

            return 0; // Passed all the above comparison macros, so must be equal.
        }

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

        enum BlendEquationEquation {
		MIN_EXT				= GL_MIN_EXT,
		MAX_EXT				= GL_MAX_EXT,
		ALPHA_MIN_SGIX			= GL_ALPHA_MIN_SGIX,
		ALPHA_MAX_SGIX			= GL_ALPHA_MAX_SGIX,
		LOGIC_OP			= GL_LOGIC_OP,
		FUNC_ADD_EXT			= GL_FUNC_ADD_EXT,
		FUNC_SUBTRACT_EXT		= GL_FUNC_SUBTRACT_EXT,
		FUNC_REVERSE_SUBTRACT_EXT	= GL_FUNC_REVERSE_SUBTRACT_EXT
        };

        inline void setEquation( GLenum equation )
        {
            _equation = equation;
        }

        inline GLenum getEquation() const { return _equation; }
        
        virtual void apply(State& state) const;
        /** Encapsulates queries of extension availability, obtains extension
          * function pointers, and provides convinience wrappers for
          * calling extension functions. */        
        class SG_EXPORT Extensions : public osg::Referenced
        {
            public:
                Extensions();

                Extensions(const Extensions& rhs);
                
                void lowestCommonDenominator(const Extensions& rhs);
                
                void setupGLExtenions();

                void setBlendEquationSupported(bool flag) { _isBlendEquationSupported=flag; }
                bool isBlendEquationSupported() const { return _isBlendEquationSupported; }
                
                void setBlendEquationProc(void* ptr) { _glBlendEquation = ptr; }
                void glBlendEquation(GLenum mode) const;

            protected:

                ~Extensions() {}
                
                bool    _isBlendEquationSupported;

                void*   _glBlendEquation;

        };
        
        /** Returns the Extensions object for the given context.
          * If createIfNotInitalized is true and the Exentsions object doesn't
          * exist, getExtensions() creates it on the given context.
          * Returns NULL if createIfNotInitalized is false and the Extensions
          * object doesn't exist. */
        static Extensions* getExtensions(unsigned int contextID,bool createIfNotInitalized);

        /** setExtensions() allows users to override the extensions across graphics contexts.
          * Typically used when you have different extensions supported across graphics pipes,
          * but need to ensure that they all use the same low common denominator extensions. */
        static void setExtensions(unsigned int contextID,Extensions* extensions);


    protected :

        virtual ~BlendEquation();


        GLenum _equation;
};

}

#endif