mapnik/agg/include/agg_span_gradient_alpha.h

//----------------------------------------------------------------------------
// Anti-Grain Geometry - Version 2.4
// Copyright (C) 2002-2005 Maxim Shemanarev (http://www.antigrain.com)
//
// Permission to copy, use, modify, sell and distribute this software 
// is granted provided this copyright notice appears in all copies. 
// This software is provided "as is" without express or implied
// warranty, and with no claim as to its suitability for any purpose.
//
//----------------------------------------------------------------------------
// Contact: mcseem@antigrain.com
//          mcseemagg@yahoo.com
//          http://www.antigrain.com
//----------------------------------------------------------------------------

#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