agg/source/agg_vpgen_clip_polygon.cpp

   1 //----------------------------------------------------------------------------
   2 // Anti-Grain Geometry - Version 2.3
   3 // Copyright (C) 2002-2005 Maxim Shemanarev (http://www.antigrain.com)
   4 //
   5 // Permission to copy, use, modify, sell and distribute this software
   6 // is granted provided this copyright notice appears in all copies.
   7 // This software is provided "as is" without express or implied
   8 // warranty, and with no claim as to its suitability for any purpose.
   9 //
  10 //----------------------------------------------------------------------------
  11 // Contact: mcseem@antigrain.com
  12 //          mcseemagg@yahoo.com
  13 //          http://www.antigrain.com
  14 //----------------------------------------------------------------------------
  15
  16 #include "agg_vpgen_clip_polygon.h"
  17 #include "agg_clip_liang_barsky.h"
  18
  19 namespace agg
  20 {
  21
  22     //------------------------------------------------------------------------
  23     // Determine the clipping code of the vertex according to the
  24     // Cyrus-Beck line clipping algorithm
  25     //
  26     //        |        |
  27     //  0110  |  0010  | 0011
  28     //        |        |
  29     // -------+--------+-------- clip_box.y2
  30     //        |        |
  31     //  0100  |  0000  | 0001
  32     //        |        |
  33     // -------+--------+-------- clip_box.y1
  34     //        |        |
  35     //  1100  |  1000  | 1001
  36     //        |        |
  37     //  clip_box.x1  clip_box.x2
  38     //
  39     //
  40     unsigned vpgen_clip_polygon::clipping_flags(double x, double y)
  41     {
  42         if(x < m_clip_box.x1)
  43         {
  44             if(y > m_clip_box.y2) return 6;
  45             if(y < m_clip_box.y1) return 12;
  46             return 4;
  47         }
  48
  49         if(x > m_clip_box.x2)
  50         {
  51             if(y > m_clip_box.y2) return 3;
  52             if(y < m_clip_box.y1) return 9;
  53             return 1;
  54         }
  55
  56         if(y > m_clip_box.y2) return 2;
  57         if(y < m_clip_box.y1) return 8;
  58
  59         return 0;
  60     }
  61
  62     //----------------------------------------------------------------------------
  63     void vpgen_clip_polygon::reset()
  64     {
  65         m_vertex = 0;
  66         m_num_vertices = 0;
  67     }
  68
  69     //----------------------------------------------------------------------------
  70     void vpgen_clip_polygon::move_to(double x, double y)
  71     {
  72         m_vertex = 0;
  73         m_num_vertices = 0;
  74         m_clip_flags = clipping_flags(x, y);
  75         if(m_clip_flags == 0)
  76         {
  77             m_x[0] = x;
  78             m_y[0] = y;
  79             m_num_vertices = 1;
  80         }
  81         m_x1  = x;
  82         m_y1  = y;
  83         m_cmd = path_cmd_move_to;
  84     }
  85
  86
  87     //----------------------------------------------------------------------------
  88     void vpgen_clip_polygon::line_to(double x, double y)
  89     {
  90         m_vertex = 0;
  91         m_num_vertices = 0;
  92         unsigned flags = clipping_flags(x, y);
  93
  94         if(m_clip_flags == flags)
  95         {
  96             if(flags == 0)
  97             {
  98                 m_x[0] = x;
  99                 m_y[0] = y;
 100                 m_num_vertices = 1;
 101             }
 102         }
 103         else
 104         {
 105             m_num_vertices = clip_liang_barsky(m_x1, m_y1,
 106                                                x, y,
 107                                                m_clip_box,
 108                                                m_x, m_y);
 109         }
 110
 111         m_clip_flags = flags;
 112         m_x1 = x;
 113         m_y1 = y;
 114     }
 115
 116
 117     //----------------------------------------------------------------------------
 118     unsigned vpgen_clip_polygon::vertex(double* x, double* y)
 119     {
 120         if(m_vertex < m_num_vertices)
 121         {
 122             *x = m_x[m_vertex];
 123             *y = m_y[m_vertex];
 124             ++m_vertex;
 125             unsigned cmd = m_cmd;
 126             m_cmd = path_cmd_line_to;
 127             return cmd;
 128         }
 129         return path_cmd_stop;
 130     }
 131
 132
 133 }