agg_span_image_filter_rgb.h

这是VCF框架的代码

                           x_lr <= maxx && y_lr <= maxy)
                        {
                            fg_ptr = (const value_type*)
                                base_type::source().row_ptr(y_lr) + x_lr + x_lr + x_lr;

                            fg[0] += weight * *fg_ptr++;
                            fg[1] += weight * *fg_ptr++;
                            fg[2] += weight * *fg_ptr++;
                            src_alpha += weight * base_mask;
                        }
                        else
                        {
                            fg[order_type::R] += back_r * weight;
                            fg[order_type::G] += back_g * weight;
                            fg[order_type::B] += back_b * weight;
                            src_alpha         += back_a * weight;
                        }

                        x_lr++;

                        weight = x_hr * (image_subpixel_scale - y_hr);
                        if(x_lr >= 0    && y_lr >= 0 &&
                           x_lr <= maxx && y_lr <= maxy)
                        {
                            fg_ptr = (const value_type*)
                                base_type::source().row_ptr(y_lr) + x_lr + x_lr + x_lr;

                            fg[0]     += weight * *fg_ptr++;
                            fg[1]     += weight * *fg_ptr++;
                            fg[2]     += weight * *fg_ptr++;
                            src_alpha += weight * base_mask;
                        }
                        else
                        {
                            fg[order_type::R] += back_r * weight;
                            fg[order_type::G] += back_g * weight;
                            fg[order_type::B] += back_b * weight;
                            src_alpha         += back_a * weight;
                        }

                        x_lr--;
                        y_lr++;

                        weight = (image_subpixel_scale - x_hr) * y_hr;
                        if(x_lr >= 0    && y_lr >= 0 &&
                           x_lr <= maxx && y_lr <= maxy)
                        {
                            fg_ptr = (const value_type*)
                                base_type::source().row_ptr(y_lr) + x_lr + x_lr + x_lr;

                            fg[0] += weight * *fg_ptr++;
                            fg[1] += weight * *fg_ptr++;
                            fg[2] += weight * *fg_ptr++;
                            src_alpha += weight * base_mask;
                        }
                        else
                        {
                            fg[order_type::R] += back_r * weight;
                            fg[order_type::G] += back_g * weight;
                            fg[order_type::B] += back_b * weight;
                            src_alpha         += back_a * weight;
                        }

                        x_lr++;

                        weight = x_hr * y_hr;
                        if(x_lr >= 0    && y_lr >= 0 &&
                           x_lr <= maxx && y_lr <= maxy)
                        {
                            fg_ptr = (const value_type*)
                                base_type::source().row_ptr(y_lr) + x_lr + x_lr + x_lr;

                            fg[0] += weight * *fg_ptr++;
                            fg[1] += weight * *fg_ptr++;
                            fg[2] += weight * *fg_ptr++;
                            src_alpha += weight * base_mask;
                        }
                        else
                        {
                            fg[order_type::R] += back_r * weight;
                            fg[order_type::G] += back_g * weight;
                            fg[order_type::B] += back_b * weight;
                            src_alpha         += back_a * weight;
                        }

                        fg[0] >>= image_subpixel_shift * 2;
                        fg[1] >>= image_subpixel_shift * 2;
                        fg[2] >>= image_subpixel_shift * 2;
                        src_alpha >>= image_subpixel_shift * 2;
                    }
                }

                span->r = (value_type)fg[order_type::R];
                span->g = (value_type)fg[order_type::G];
                span->b = (value_type)fg[order_type::B];
                span->a = (value_type)src_alpha;
                ++span;
                ++base_type::interpolator();

            } while(--len);
        }
    private:
        color_type m_back_color;
    };



    //===============================================span_image_filter_rgb_2x2
    template<class Source, class Interpolator> 
    class span_image_filter_rgb_2x2 : 
    public span_image_filter<Source, Interpolator>
    {
    public:
        typedef Source source_type;
        typedef typename source_type::color_type color_type;
        typedef typename source_type::order_type order_type;
        typedef Interpolator interpolator_type;
        typedef span_image_filter<source_type, interpolator_type> base_type;
        typedef typename color_type::value_type value_type;
        typedef typename color_type::calc_type calc_type;
        enum base_scale_e
        {
            base_shift = color_type::base_shift,
            base_mask  = color_type::base_mask
        };

        //--------------------------------------------------------------------
        span_image_filter_rgb_2x2() {}
        span_image_filter_rgb_2x2(source_type& src, 
                                  interpolator_type& inter,
                                  const image_filter_lut& filter) :
            base_type(src, inter, &filter) 
        {}


        //--------------------------------------------------------------------
        void generate(color_type* span, int x, int y, unsigned len)
        {
            base_type::interpolator().begin(x + base_type::filter_dx_dbl(), 
                                            y + base_type::filter_dy_dbl(), len);

            calc_type fg[3];

            const value_type *fg_ptr;
            const int16* weight_array = base_type::filter().weight_array() + 
                                        ((base_type::filter().diameter()/2 - 1) << 
                                          image_subpixel_shift);
            do
            {
                int x_hr;
                int y_hr;

                base_type::interpolator().coordinates(&x_hr, &y_hr);

                x_hr -= base_type::filter_dx_int();
                y_hr -= base_type::filter_dy_int();

                int x_lr = x_hr >> image_subpixel_shift;
                int y_lr = y_hr >> image_subpixel_shift;

                unsigned weight;
                fg[0] = fg[1] = fg[2] = image_filter_scale / 2;

                x_hr &= image_subpixel_mask;
                y_hr &= image_subpixel_mask;

                fg_ptr = (const value_type*)base_type::source().span(x_lr, y_lr, 2);
                weight = (weight_array[x_hr + image_subpixel_scale] * 
                          weight_array[y_hr + image_subpixel_scale] + 
                          image_filter_scale / 2) >> 
                          image_filter_shift;
                fg[0] += weight * *fg_ptr++;
                fg[1] += weight * *fg_ptr++;
                fg[2] += weight * *fg_ptr;

                fg_ptr = (const value_type*)base_type::source().next_x();
                weight = (weight_array[x_hr] * 
                          weight_array[y_hr + image_subpixel_scale] + 
                          image_filter_scale / 2) >> 
                          image_filter_shift;
                fg[0] += weight * *fg_ptr++;
                fg[1] += weight * *fg_ptr++;
                fg[2] += weight * *fg_ptr;

                fg_ptr = (const value_type*)base_type::source().next_y();
                weight = (weight_array[x_hr + image_subpixel_scale] * 
                          weight_array[y_hr] + 
                          image_filter_scale / 2) >> 
                          image_filter_shift;
                fg[0] += weight * *fg_ptr++;
                fg[1] += weight * *fg_ptr++;
                fg[2] += weight * *fg_ptr;

                fg_ptr = (const value_type*)base_type::source().next_x();
                weight = (weight_array[x_hr] * 
                          weight_array[y_hr] + 
                          image_filter_scale / 2) >> 
                          image_filter_shift;
                fg[0] += weight * *fg_ptr++;
                fg[1] += weight * *fg_ptr++;
                fg[2] += weight * *fg_ptr;

                fg[0] >>= image_filter_shift;
                fg[1] >>= image_filter_shift;
                fg[2] >>= image_filter_shift;

                if(fg[order_type::R] > base_mask) fg[order_type::R] = base_mask;
                if(fg[order_type::G] > base_mask) fg[order_type::G] = base_mask;
                if(fg[order_type::B] > base_mask) fg[order_type::B] = base_mask;

                span->r = (value_type)fg[order_type::R];
                span->g = (value_type)fg[order_type::G];
                span->b = (value_type)fg[order_type::B];
                span->a = base_mask;

                ++span;
                ++base_type::interpolator();

            } while(--len);
        }
    };



    //===================================================span_image_filter_rgb
    template<class Source, class Interpolator> 
    class span_image_filter_rgb : 
    public span_image_filter<Source, Interpolator>
    {
    public:
        typedef Source source_type;
        typedef typename source_type::color_type color_type;
        typedef typename source_type::order_type order_type;
        typedef Interpolator interpolator_type;
        typedef span_image_filter<source_type, interpolator_type> base_type;
        typedef typename color_type::value_type value_type;
        typedef typename color_type::calc_type calc_type;
        enum base_scale_e
        {
            base_shift = color_type::base_shift,
            base_mask  = color_type::base_mask
        };

        //--------------------------------------------------------------------
        span_image_filter_rgb() {}
        span_image_filter_rgb(source_type& src, 
                              interpolator_type& inter,
                              const image_filter_lut& filter) :
            base_type(src, inter, &filter) 
        {}

        //--------------------------------------------------------------------
        void generate(color_type* span, int x, int y, unsigned len)
        {
            base_type::interpolator().begin(x + base_type::filter_dx_dbl(), 
                                            y + base_type::filter_dy_dbl(), len);

            int fg[3];
            const value_type *fg_ptr;

            unsigned     diameter     = base_type::filter().diameter();
            int          start        = base_type::filter().start();
            const int16* weight_array = base_type::filter().weight_array();

            int x_count; 
            int weight_y;

            do
            {
                base_type::interpolator().coordinates(&x, &y);

                x -= base_type::filter_dx_int();
                y -= base_type::filter_dy_int();

                int x_hr = x; 
                int y_hr = y; 

                int x_lr = x_hr >> image_subpixel_shift;
                int y_lr = y_hr >> image_subpixel_shift;

                fg[0] = fg[1] = fg[2] = image_filter_scale / 2;

                int x_fract = x_hr & image_subpixel_mask;
                unsigned y_count = diameter;

                y_hr = image_subpixel_mask - (y_hr & image_subpixel_mask);
                fg_ptr = (const value_type*)base_type::source().span(x_lr + start, 
                                                                     y_lr + start, 
                                                                     diameter);
                for(;;)
                {
                    x_count  = diameter;
                    weight_y = weight_array[y_hr];
                    x_hr = image_subpixel_mask - x_fract;
                    for(;;)
                    {
                        int weight = (weight_y * weight_array[x_hr] + 
                                     image_filter_scale / 2) >> 
                                     image_filter_shift;

                        fg[0] += weight * *fg_ptr++;
                        fg[1] += weight * *fg_ptr++;
                        fg[2] += weight * *fg_ptr;

                        if(--x_count == 0) break;
                        x_hr  += image_subpixel_scale;