PolygonOffset

/* -*-c++-*- OpenSceneGraph - Copyright (C) 1998-2006 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_POLYGONOFFSET
#define OSG_POLYGONOFFSET 1

#include <osg/StateAttribute>

#ifndef GL_POLYGON_OFFSET_LINE 
    #define GL_POLYGON_OFFSET_LINE 0x2A02
    #define GL_POLYGON_OFFSET_POINT 0x2A01
#endif

namespace osg {

/** PolygonOffset - encapsulates the OpenGL glPolygonOffset state.*/
class OSG_EXPORT PolygonOffset : public StateAttribute
{
    public :

        PolygonOffset();

        PolygonOffset(float factor, float units);

        /** Copy constructor using CopyOp to manage deep vs shallow copy.*/
        PolygonOffset(const PolygonOffset& po,const CopyOp& copyop=CopyOp::SHALLOW_COPY):
            StateAttribute(po,copyop),
            _factor(po._factor),
            _units(po._units) {}

        META_StateAttribute(osg, PolygonOffset, POLYGONOFFSET);

        /** 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_Parameter macros below.
            COMPARE_StateAttribute_Types(PolygonOffset,sa)

            // compare each parameter in turn against the rhs.
            COMPARE_StateAttribute_Parameter(_factor)
            COMPARE_StateAttribute_Parameter(_units)

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

        virtual bool getModeUsage(StateAttribute::ModeUsage& usage) const
        {
            usage.usesMode(GL_POLYGON_OFFSET_FILL);
#if !defined(OSG_GLES1_AVAILABLE) && !defined(OSG_GLES2_AVAILABLE)
            usage.usesMode(GL_POLYGON_OFFSET_LINE);
            usage.usesMode(GL_POLYGON_OFFSET_POINT);
#endif
            return true;
        }

        inline void setFactor(float factor) { _factor = factor; }
        inline float getFactor() const { return _factor; }
        
        inline void setUnits(float units) { _units = units; }
        inline float getUnits() const { return _units; }

        virtual void apply(State& state) const;


        static void setFactorMultiplier(float multiplier);
        static float getFactorMultiplier();

        static void setUnitsMultiplier(float multiplier);
        static float getUnitsMultiplier();
        
        static bool areFactorAndUnitsMultipliersSet();
        
        /** Checks with the OpenGL driver to try and pick multiplier appropriate for the hardware.
            note, requires a valid graphics context to be current. */
        static void setFactorAndUnitsMultipliersUsingBestGuessForDriver();

    protected :

        virtual ~PolygonOffset();

        float       _factor;
        float       _units;

};

}

#endif