agg_rasterizer_scanline_aa.h

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//----------------------------------------------------------------------------
// 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.
//
//----------------------------------------------------------------------------
//
// The author gratefully acknowleges the support of David Turner, 
// Robert Wilhelm, and Werner Lemberg - the authors of the FreeType 
// libray - in producing this work. See http://www.freetype.org for details.
//
//----------------------------------------------------------------------------
// Contact: [e-mail]
//          [e-mail]
//          http://www.antigrain.com
//----------------------------------------------------------------------------
//
// Adaptation for 32-bit screen coordinates has been sponsored by 
// Liberty Technology Systems, Inc., visit http://lib-sys.com
//
// Liberty Technology Systems, Inc. is the provider of
// PostScript and PDF technology for software developers.
// 
//----------------------------------------------------------------------------
#ifndef AGG_RASTERIZER_SCANLINE_AA_INCLUDED
#define AGG_RASTERIZER_SCANLINE_AA_INCLUDED

#include "agg_rasterizer_cells_aa.h"
#include "agg_rasterizer_sl_clip.h"
#include "agg_gamma_functions.h"


namespace agg
{


    //-----------------------------------------------------------------cell_aa
    // A pixel cell. There're no constructors defined and it was done 
    // intentionally in order to avoid extra overhead when allocating an 
    // array of cells.
    struct cell_aa
    {
        int x;
        int y;
        int cover;
        int area;

        void initial()
        {
            x = 0x7FFFFFFF;
            y = 0x7FFFFFFF;
            cover = 0;
            area  = 0;
        }

        void style(const cell_aa&) {}

        int not_equal(int ex, int ey, const cell_aa&) const
        {
            return (ex - x) | (ey - y);
        }
    };


    //==================================================rasterizer_scanline_aa
    // Polygon rasterizer that is used to render filled polygons with 
    // high-quality Anti-Aliasing. Internally, by default, the class uses 
    // integer coordinates in format 24.8, i.e. 24 bits for integer part 
    // and 8 bits for fractional - see poly_subpixel_shift. This class can be 
    // used in the following  way:
    //
    // 1. filling_rule(filling_rule_e ft) - optional.
    //
    // 2. gamma() - optional.
    //
    // 3. reset()
    //
    // 4. move_to(x, y) / line_to(x, y) - make the polygon. One can create 
    //    more than one contour, but each contour must consist of at least 3
    //    vertices, i.e. move_to(x1, y1); line_to(x2, y2); line_to(x3, y3);
    //    is the absolute minimum of vertices that define a triangle.
    //    The algorithm does not check either the number of vertices nor
    //    coincidence of their coordinates, but in the worst case it just 
    //    won't draw anything.
    //    The orger of the vertices (clockwise or counterclockwise) 
    //    is important when using the non-zero filling rule (fill_non_zero).
    //    In this case the vertex order of all the contours must be the same
    //    if you want your intersecting polygons to be without "holes".
    //    You actually can use different vertices order. If the contours do not 
    //    intersect each other the order is not important anyway. If they do, 
    //    contours with the same vertex order will be rendered without "holes" 
    //    while the intersecting contours with different orders will have "holes".
    //
    // filling_rule() and gamma() can be called anytime before "sweeping".
    //------------------------------------------------------------------------
    template<class Clip=rasterizer_sl_clip_int> class rasterizer_scanline_aa
    {
        enum status
        {
            status_initial,
            status_move_to,
            status_line_to,
            status_closed
        };

    public:
        typedef Clip                      clip_type;
        typedef typename Clip::conv_type  conv_type;
        typedef typename Clip::coord_type coord_type;

        enum aa_scale_e
        {
            aa_shift  = 8,
            aa_scale  = 1 << aa_shift,
            aa_mask   = aa_scale - 1,
            aa_scale2 = aa_scale * 2,
            aa_mask2  = aa_scale2 - 1
        };

        //--------------------------------------------------------------------
        rasterizer_scanline_aa() : 
            m_outline(),
            m_clipper(),
            m_filling_rule(fill_non_zero),
            m_auto_close(true),
            m_start_x(0),
            m_start_y(0),
            m_status(status_initial)
        {
            int i;
            for(i = 0; i < aa_scale; i++) m_gamma[i] = i;
        }

        //--------------------------------------------------------------------
        template<class GammaF> 
        rasterizer_scanline_aa(const GammaF& gamma_function) : 
            m_outline(),
            m_clipper(m_outline),
            m_filling_rule(fill_non_zero),
            m_auto_close(true),
            m_start_x(0),
            m_start_y(0),
            m_status(status_initial)
        {
            gamma(gamma_function);
        }

        //--------------------------------------------------------------------
        void reset(); 
        void reset_clipping();
        void clip_box(double x1, double y1, double x2, double y2);
        void filling_rule(filling_rule_e filling_rule);
        void auto_close(bool flag) { m_auto_close = flag; }

        //--------------------------------------------------------------------
        template<class GammaF> void gamma(const GammaF& gamma_function)
        { 
            int i;
            for(i = 0; i < aa_scale; i++)
            {
                m_gamma[i] = uround(gamma_function(double(i) / aa_mask) * aa_mask);
            }
        }

        //--------------------------------------------------------------------
        unsigned apply_gamma(unsigned cover) const 
        { 
            return m_gamma[cover]; 
        }

        //--------------------------------------------------------------------
        void move_to(int x, int y);
        void line_to(int x, int y);
        void move_to_d(double x, double y);
        void line_to_d(double x, double y);
        void close_polygon();
        void add_vertex(double x, double y, unsigned cmd);

        void edge(int x1, int y1, int x2, int y2);
        void edge_d(double x1, double y1, double x2, double y2);

        //-------------------------------------------------------------------
        template<class VertexSource>
        void add_path(VertexSource& vs, unsigned path_id=0)
        {
            double x;
            double y;

            unsigned cmd;
            vs.rewind(path_id);
            if(m_outline.sorted()) reset();
            while(!is_stop(cmd = vs.vertex(&x, &y)))
            {
                add_vertex(x, y, cmd);
            }
        }
        
        //--------------------------------------------------------------------
        int min_x() const { return m_outline.min_x(); }
        int min_y() const { return m_outline.min_y(); }
        int max_x() const { return m_outline.max_x(); }
        int max_y() const { return m_outline.max_y(); }

        //--------------------------------------------------------------------
        void sort();
        bool rewind_scanlines();
        bool navigate_scanline(int y);

        //--------------------------------------------------------------------
        AGG_INLINE unsigned calculate_alpha(int area) const
        {
            int cover = area >> (poly_subpixel_shift*2 + 1 - aa_shift);

            if(cover < 0) cover = -cover;
            if(m_filling_rule == fill_even_odd)
            {
                cover &= aa_mask2;
                if(cover > aa_scale)
                {
                    cover = aa_scale2 - cover;
                }
            }
            if(cover > aa_mask) cover = aa_mask;
            return m_gamma[cover];
        }

        //--------------------------------------------------------------------
        template<class Scanline> bool sweep_scanline(Scanline& sl)
        {
            for(;;)
            {
                if(m_scan_y > m_outline.max_y()) return false;
                sl.reset_spans();
                unsigned num_cells = m_outline.scanline_num_cells(m_scan_y);
                const cell_aa* const* cells = m_outline.scanline_cells(m_scan_y);
                int cover = 0;

                while(num_cells)
                {
                    const cell_aa* cur_cell = *cells;
                    int x    = cur_cell->x;
                    int area = cur_cell->area;
                    unsigned alpha;

                    cover += cur_cell->cover;

                    //accumulate all cells with the same X
                    while(--num_cells)
                    {
                        cur_cell = *++cells;