agg-2.5/include/agg_span_gradient_alpha.h

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//----------------------------------------------------------------------------
// Anti-Grain Geometry (AGG) - Version 2.5
// A high quality rendering engine for C++
// Copyright (C) 2002-2006 Maxim Shemanarev
// Contact: mcseem@antigrain.com
//          mcseemagg@yahoo.com
//          http://antigrain.com
// 
// AGG is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
// 
// AGG 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
// GNU General Public License for more details.
// 
// You should have received a copy of the GNU General Public License
// along with AGG; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, 
// MA 02110-1301, USA.
//----------------------------------------------------------------------------

#ifndef AGG_SPAN_GRADIENT_ALPHA_INCLUDED
#define AGG_SPAN_GRADIENT_ALPHA_INCLUDED

#include "agg_span_gradient.h"

namespace agg
{
    //======================================================span_gradient_alpha
    template<class ColorT, 
             class Interpolator,
             class GradientF, 
             class AlphaF>
    class span_gradient_alpha
    {
    public:
        typedef Interpolator interpolator_type;
        typedef ColorT color_type;
        typedef typename color_type::value_type alpha_type;

        enum downscale_shift_e
        {
            downscale_shift = interpolator_type::subpixel_shift - gradient_subpixel_shift
        };


        //--------------------------------------------------------------------
        span_gradient_alpha() {}

        //--------------------------------------------------------------------
        span_gradient_alpha(interpolator_type& inter,
                            const GradientF& gradient_function,
                            const AlphaF& alpha_function,
                            double d1, double d2) : 
            m_interpolator(&inter),
            m_gradient_function(&gradient_function),
            m_alpha_function(&alpha_function),
            m_d1(iround(d1 * gradient_subpixel_scale)),
            m_d2(iround(d2 * gradient_subpixel_scale))
        {}

        //--------------------------------------------------------------------
        interpolator_type& interpolator() { return *m_interpolator; }
        const GradientF& gradient_function() const { return *m_gradient_function; }
        const AlphaF& alpha_function() const { return *m_alpha_function; }
        double d1() const { return double(m_d1) / gradient_subpixel_scale; }
        double d2() const { return double(m_d2) / gradient_subpixel_scale; }

        //--------------------------------------------------------------------
        void interpolator(interpolator_type& i) { m_interpolator = &i; }
        void gradient_function(const GradientF& gf) { m_gradient_function = &gf; }
        void alpha_function(const AlphaF& af) { m_alpha_function = &af; }
        void d1(double v) { m_d1 = iround(v * gradient_subpixel_scale); }
        void d2(double v) { m_d2 = iround(v * gradient_subpixel_scale); }

        //--------------------------------------------------------------------
        void prepare() {}

        //--------------------------------------------------------------------
        void generate(color_type* span, int x, int y, unsigned len)
        {   
            int dd = m_d2 - m_d1;
            if(dd < 1) dd = 1;
            m_interpolator->begin(x+0.5, y+0.5, len);
            do
            {
                m_interpolator->coordinates(&x, &y);
                int d = m_gradient_function->calculate(x >> downscale_shift, 
                                                       y >> downscale_shift, m_d2);
                d = ((d - m_d1) * (int)m_alpha_function->size()) / dd;
                if(d < 0) d = 0;
                if(d >= (int)m_alpha_function->size()) d = m_alpha_function->size() - 1;
                span->a = (*m_alpha_function)[d];
                ++span;
                ++(*m_interpolator);
            }
            while(--len);
        }

    private:
        interpolator_type* m_interpolator;
        const GradientF*   m_gradient_function;
        const AlphaF*      m_alpha_function;
        int                m_d1;
        int                m_d2;
    };


    //=======================================================gradient_alpha_x
    template<class ColorT> struct gradient_alpha_x
    {
        typedef typename ColorT::value_type alpha_type;
        alpha_type operator [] (alpha_type x) const { return x; }
    };

    //====================================================gradient_alpha_x_u8
    struct gradient_alpha_x_u8
    {
        typedef int8u alpha_type;
        alpha_type operator [] (alpha_type x) const { return x; }
    };

    //==========================================gradient_alpha_one_munus_x_u8
    struct gradient_alpha_one_munus_x_u8
    {
        typedef int8u alpha_type;
        alpha_type operator [] (alpha_type x) const { return 255-x; }
    };

}

#endif