mapnik/agg/include/agg_span_gradient.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_INCLUDED
#define AGG_SPAN_GRADIENT_INCLUDED

#include <math.h>
#include <stdlib.h>
#include <string.h>
#include "agg_basics.h"
#include "agg_math.h"
#include "agg_array.h"


namespace agg
{

    enum gradient_subpixel_scale_e
    {
        gradient_subpixel_shift = 4,                              //-----gradient_subpixel_shift
        gradient_subpixel_scale = 1 << gradient_subpixel_shift,   //-----gradient_subpixel_scale
        gradient_subpixel_mask  = gradient_subpixel_scale - 1     //-----gradient_subpixel_mask
    };



    //==========================================================span_gradient
    template<class ColorT,
             class Interpolator,
             class GradientF, 
             class ColorF>
    class span_gradient
    {
    public:
        typedef Interpolator interpolator_type;
        typedef ColorT color_type;

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

        //--------------------------------------------------------------------
        span_gradient() {}

        //--------------------------------------------------------------------
        span_gradient(interpolator_type& inter,
                      const GradientF& gradient_function,
                      const ColorF& color_function,
                      double d1, double d2) : 
            m_interpolator(&inter),
            m_gradient_function(&gradient_function),
            m_color_function(&color_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 ColorF& color_function() const { return *m_color_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 color_function(const ColorF& cf) { m_color_function = &cf; }
        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_color_function->size()) / dd;
                if(d < 0) d = 0;
                if(d >= (int)m_color_function->size()) d = m_color_function->size() - 1;
                *span++ = (*m_color_function)[d];
                ++(*m_interpolator);
            }
            while(--len);
        }

    private:
        interpolator_type* m_interpolator;
        const GradientF*   m_gradient_function;
        const ColorF*      m_color_function;
        int                m_d1;
        int                m_d2;
    };




    //=====================================================gradient_linear_color
    template<class ColorT> 
    struct gradient_linear_color
    {
        typedef ColorT color_type;

        gradient_linear_color() {}
        gradient_linear_color(const color_type& c1, const color_type& c2, 
                              unsigned size = 256) :
            m_c1(c1), m_c2(c2), m_size(size) {}

        unsigned size() const { return m_size; }
        color_type operator [] (unsigned v) const 
        {
            return m_c1.gradient(m_c2, double(v) / double(m_size - 1));
        }

        void colors(const color_type& c1, const color_type& c2, unsigned size = 256)
        {
            m_c1 = c1;
            m_c2 = c2;
            m_size = size;
        }

        color_type m_c1;
        color_type m_c2;
        unsigned m_size;
    };


    //==========================================================gradient_circle
    class gradient_circle
    {
        // Actually the same as radial. Just for compatibility
    public:
        static AGG_INLINE int calculate(int x, int y, int)
        {
            return int(fast_sqrt(x*x + y*y));
        }
    };


    //==========================================================gradient_radial
    class gradient_radial
    {
    public:
        static AGG_INLINE int calculate(int x, int y, int)
        {
            return int(fast_sqrt(x*x + y*y));
        }
    };


    //========================================================gradient_radial_d
    class gradient_radial_d
    {
    public:
        static AGG_INLINE int calculate(int x, int y, int)
        {
            return uround(sqrt(double(x)*double(x) + double(y)*double(y)));
        }
    };


    //====================================================gradient_radial_focus
    class gradient_radial_focus
    {
    public:
        //---------------------------------------------------------------------
        gradient_radial_focus() : 
            m_radius(100 * gradient_subpixel_scale), 
            m_focus_x(0), 
            m_focus_y(0)
        {
            update_values();
        }

        //---------------------------------------------------------------------
        gradient_radial_focus(double r, double fx, double fy) : 
            m_radius (iround(r  * gradient_subpixel_scale)), 
            m_focus_x(iround(fx * gradient_subpixel_scale)), 
            m_focus_y(iround(fy * gradient_subpixel_scale))
        {
            update_values();
        }

        //---------------------------------------------------------------------
        void init(double r, double fx, double fy)
        {
            m_radius  = iround(r  * gradient_subpixel_scale);
            m_focus_x = iround(fx * gradient_subpixel_scale);
            m_focus_y = iround(fy * gradient_subpixel_scale);
            update_values();
        }

        //---------------------------------------------------------------------
        double radius()  const { return double(m_radius)  / gradient_subpixel_scale; }
        double focus_x() const { return double(m_focus_x) / gradient_subpixel_scale; }
        double focus_y() const { return double(m_focus_y) / gradient_subpixel_scale; }

        //---------------------------------------------------------------------
        int calculate(int x, int y, int) const
        {
            double solution_x;
            double solution_y;

            // Special case to avoid divide by zero or very near zero
            //---------------------------------
            if(x == iround(m_focus_x))
            {		   
                solution_x = m_focus_x;
                solution_y = 0.0;
                solution_y += (y > m_focus_y) ? m_trivial : -m_trivial;
            }
            else 
            {    
                // Slope of the focus-current line
                //-------------------------------
                double slope = double(y - m_focus_y) / double(x - m_focus_x);

                // y-intercept of that same line
                //--------------------------------
                double yint  = double(y) - (slope * x); 
		
                // Use the classical quadratic formula to calculate 
                // the intersection point		  
                //--------------------------------
                double a = (slope * slope) + 1; 
                double b =  2 * slope * yint;
                double c =  yint * yint - m_radius2;
                double det = sqrt((b * b) - (4.0 * a * c));
		        solution_x = -b;
		
                // Choose the positive or negative root depending
                // on where the X coord lies with respect to the focus.
                solution_x += (x < m_focus_x) ? -det : det;
		        solution_x /= 2.0 * a;

                // Calculating of Y is trivial
                solution_y  = (slope * solution_x) + yint;
            }	                    	

            // Calculate the percentage (0...1) of the current point along the 
            // focus-circumference line and return the normalized (0...d) value
            //-------------------------------
            solution_x -= double(m_focus_x);
            solution_y -= double(m_focus_y);
            double int_to_focus = solution_x * solution_x + solution_y * solution_y;
            double cur_to_focus = double(x - m_focus_x) * double(x - m_focus_x) +
                                  double(y - m_focus_y) * double(y - m_focus_y);

            return iround(sqrt(cur_to_focus / int_to_focus) * m_radius);
        }

    private:
        //---------------------------------------------------------------------
        void update_values()
        {
            // For use in the quadratic equation
            //-------------------------------
            m_radius2 = double(m_radius) * double(m_radius);

            double dist = sqrt(double(m_focus_x) * double(m_focus_x) + 
                               double(m_focus_y) * double(m_focus_y));

            // Test if distance from focus to center is greater than the radius
            // For the sake of assurance factor restrict the point to be 
            // no further than 99% of the radius.
            //-------------------------------
            double r = m_radius * 0.99;
            if(dist > r) 
            { 
                // clamp focus to radius
                // x = r cos theta, y = r sin theta
                //------------------------
                double a = atan2(double(m_focus_y), double(m_focus_x));
                m_focus_x = iround(r * cos(a));
                m_focus_y = iround(r * sin(a));
            }

            // Calculate the solution to be used in the case where x == focus_x
            //------------------------------
            m_trivial = sqrt(m_radius2 - (m_focus_x * m_focus_x));
        }

        int m_radius;
        int m_focus_x;
        int m_focus_y;
        double m_radius2;
        double m_trivial;
    };



    //==============================================================gradient_x
    class gradient_x
    {
    public:
        static int calculate(int x, int, int) { return x; }
    };


    //==============================================================gradient_y
    class gradient_y
    {
    public:
        static int calculate(int, int y, int) { return y; }
    };


    //========================================================gradient_diamond
    class gradient_diamond
    {
    public:
        static AGG_INLINE int calculate(int x, int y, int) 
        { 
            int ax = abs(x);
            int ay = abs(y);
            return ax > ay ? ax : ay; 
        }
    };


    //=============================================================gradient_xy
    class gradient_xy
    {
    public:
        static AGG_INLINE int calculate(int x, int y, int d) 
        { 
            return abs(x) * abs(y) / d; 
        }
    };


    //========================================================gradient_sqrt_xy
    class gradient_sqrt_xy
    {
    public:
        static AGG_INLINE int calculate(int x, int y, int) 
        { 
            return fast_sqrt(abs(x) * abs(y)); 
        }
    };


    //==========================================================gradient_conic
    class gradient_conic
    {
    public:
        static AGG_INLINE int calculate(int x, int y, int d) 
        { 
            return uround(fabs(atan2(double(y), double(x))) * double(d) / pi);
        }
    };


    //=================================================gradient_repeat_adaptor
    template<class GradientF> class gradient_repeat_adaptor
    {
    public:
        gradient_repeat_adaptor(const GradientF& gradient) : 
            m_gradient(&gradient) {}

        AGG_INLINE int calculate(int x, int y, int d) const
        {
            int ret = m_gradient->calculate(x, y, d) % d;
            if(ret < 0) ret += d;
            return ret;
        }

    private:
        const GradientF* m_gradient;
    };


    //================================================gradient_reflect_adaptor
    template<class GradientF> class gradient_reflect_adaptor
    {
    public:
        gradient_reflect_adaptor(const GradientF& gradient) : 
            m_gradient(&gradient) {}

        AGG_INLINE int calculate(int x, int y, int d) const
        {
            int d2 = d << 1;
            int ret = m_gradient->calculate(x, y, d) % d2;
            if(ret <  0) ret += d2;
            if(ret >= d) ret  = d2 - ret;
            return ret;
        }

    private:
        const GradientF* m_gradient;
    };


}

#endif