src/Geo/GeoClip.hpp

   1 /*
   2 Copyright_License {
   3
   4   XCSoar Glide Computer - http://www.xcsoar.org/
   5   Copyright (C) 2000-2013 The XCSoar Project
   6   A detailed list of copyright holders can be found in the file "AUTHORS".
   7
   8   This program is free software; you can redistribute it and/or
   9   modify it under the terms of the GNU General Public License
  10   as published by the Free Software Foundation; either version 2
  11   of the License, or (at your option) any later version.
  12
  13   This program is distributed in the hope that it will be useful,
  14   but WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16   GNU General Public License for more details.
  17
  18   You should have received a copy of the GNU General Public License
  19   along with this program; if not, write to the Free Software
  20   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  21 }
  22 */
  23
  24 #ifndef XCSOAR_GEO_CLIP_HPP
  25 #define XCSOAR_GEO_CLIP_HPP
  26
  27 #include "Geo/GeoBounds.hpp"
  28 #include "Compiler.h"
  29
  30 /**
  31  * A rectangle on earth's surface with very simple semantics.  Similar
  32  * to the RECT struct, it is bounded by four orthogonal lines.  Its
  33  * goal is to perform fast overlap checks, e.g. to determine if an
  34  * object is visible on the screen.
  35  */
  36 class GeoClip : protected GeoBounds {
  37   Angle width;
  38
  39 public:
  40   GeoClip() = default;
  41   GeoClip(const GeoBounds &other)
  42     :GeoBounds(other), width(GetWidth()) {}
  43
  44 protected:
  45   /**
  46    * Imports a longitude value.  To avoid wraparound bugs, all
  47    * longitudes used internally in this class are relative to the
  48    * "west" bound.
  49    */
  50   gcc_pure
  51   Angle ImportLongitude(Angle l) const {
  52     return (l - GetWest()).AsDelta();
  53   }
  54
  55   gcc_pure
  56   GeoPoint ImportPoint(GeoPoint pt) const {
  57     return GeoPoint(ImportLongitude(pt.longitude), pt.latitude);
  58   }
  59
  60   gcc_pure
  61   GeoPoint ExportPoint(GeoPoint pt) const {
  62     return GeoPoint(pt.longitude + GetWest(), pt.latitude);
  63   }
  64
  65   /**
  66    * Clips a point to be bounds.
  67    *
  68    * @param pt the point to be clipped (in and out)
  69    * @return false if neither origin nor pt are visible
  70    */
  71   bool ClipPoint(const GeoPoint &origin, GeoPoint &pt) const;
  72
  73   /**
  74    * Clips a vertex.
  75    *
  76    * @param prev the previous vertex
  77    * @param pt the vertex to be clipped (in and out)
  78    * @param insert an array of up to two vertices to be inserted after pt
  79    * @param next the next vertex
  80    * @return the new number of vertices between prev and next (e.g. 0
  81    * deletes, 1 preserves, 2 or 3 insert new ones)
  82    */
  83   unsigned ClipVertex(const GeoPoint &prev, GeoPoint &pt, GeoPoint *insert,
  84                       const GeoPoint &next) const;
  85
  86 public:
  87   /**
  88    * Makes sure that the line does not exceed the bounds.  This method
  89    * is not designed to perform strict clipping, it is just here to
  90    * avoid integer overflows in the graphics drivers.
  91    *
  92    * @return false if the line is definitely outside the bounds
  93    * rectangle
  94    */
  95   bool ClipLine(GeoPoint &a, GeoPoint &b) const;
  96
  97   /**
  98    * Makes sure that the polygon does not exceed the bounds.  This
  99    * method is not designed to perform strict clipping, it is just
 100    * here to avoid integer overflows in the graphics drivers.
 101    *
 102    * The implementation is a specialization of the Sutherland-Hodgman
 103    * algorithm, with only horizontal and vertical bound lines.
 104    *
 105    * @param dest a GeoPoint array with enough space for three times
 106    * src_length
 107    * @return the number of vertices written to dest; if less than 3,
 108    * then the polygon can not be drawn
 109    */
 110   unsigned ClipPolygon(GeoPoint *dest,
 111                        const GeoPoint *src, unsigned src_length) const;
 112 };
 113
 114 #endif