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  67
  68   <div class="section" id="point">
  69 <h1>Point</h1>
  70 <div class="contents local topic" id="contents">
  71 <ul class="simple">
  72 <li><a class="reference internal" href="#overview" id="id1">Overview</a></li>
  73 <li><a class="reference internal" href="#models" id="id2">Models</a></li>
  74 </ul>
  75 </div>
  76 <div class="section" id="overview">
  77 <h2><a class="toc-backref" href="#id1">Overview</a></h2>
  78 <p>A point defines the location of a pixel inside an image. It can also be used
  79 to describe the dimensions of an image. In most general terms, points are
  80 N-dimensional and model the following concept:</p>
  81 <div class="highlight-cpp"><div class="highlight"><pre><span class="n">concept</span> <span class="n">PointNDConcept</span><span class="o">&lt;</span><span class="k">typename</span> <span class="n">T</span><span class="o">&gt;</span> <span class="o">:</span> <span class="n">Regular</span><span class="o">&lt;</span><span class="n">T</span><span class="o">&gt;</span>
  82 <span class="p">{</span>
  83     <span class="c1">// the type of a coordinate along each axis</span>
  84     <span class="k">template</span> <span class="o">&lt;</span><span class="kt">size_t</span> <span class="n">K</span><span class="o">&gt;</span> <span class="k">struct</span> <span class="n">axis</span><span class="p">;</span> <span class="n">where</span> <span class="n">Metafunction</span><span class="o">&lt;</span><span class="n">axis</span><span class="o">&gt;</span><span class="p">;</span>
  85
  86     <span class="k">const</span> <span class="kt">size_t</span> <span class="n">num_dimensions</span><span class="p">;</span>
  87
  88     <span class="c1">// accessor/modifier of the value of each axis.</span>
  89     <span class="k">template</span> <span class="o">&lt;</span><span class="kt">size_t</span> <span class="n">K</span><span class="o">&gt;</span> <span class="k">const</span> <span class="k">typename</span> <span class="n">axis</span><span class="o">&lt;</span><span class="n">K</span><span class="o">&gt;::</span><span class="n">type</span><span class="o">&amp;</span> <span class="n">T</span><span class="o">::</span><span class="n">axis_value</span><span class="p">()</span> <span class="k">const</span><span class="p">;</span>
  90     <span class="k">template</span> <span class="o">&lt;</span><span class="kt">size_t</span> <span class="n">K</span><span class="o">&gt;</span>       <span class="k">typename</span> <span class="n">axis</span><span class="o">&lt;</span><span class="n">K</span><span class="o">&gt;::</span><span class="n">type</span><span class="o">&amp;</span> <span class="n">T</span><span class="o">::</span><span class="n">axis_value</span><span class="p">();</span>
  91 <span class="p">};</span>
  92 </pre></div>
  93 </div>
  94 <p>GIL uses a two-dimensional point, which is a refinement of <code class="docutils literal"><span class="pre">PointNDConcept</span></code>
  95 in which both dimensions are of the same type:</p>
  96 <div class="highlight-cpp"><div class="highlight"><pre><span class="n">concept</span> <span class="n">Point2DConcept</span><span class="o">&lt;</span><span class="k">typename</span> <span class="n">T</span><span class="o">&gt;</span> <span class="o">:</span> <span class="n">PointNDConcept</span><span class="o">&lt;</span><span class="n">T</span><span class="o">&gt;</span>
  97 <span class="p">{</span>
  98     <span class="n">where</span> <span class="n">num_dimensions</span> <span class="o">==</span> <span class="mi">2</span><span class="p">;</span>
  99     <span class="n">where</span> <span class="n">SameType</span><span class="o">&lt;</span><span class="n">axis</span><span class="o">&lt;</span><span class="mi">0</span><span class="o">&gt;::</span><span class="n">type</span><span class="p">,</span> <span class="n">axis</span><span class="o">&lt;</span><span class="mi">1</span><span class="o">&gt;::</span><span class="n">type</span><span class="o">&gt;</span><span class="p">;</span>
 100
 101     <span class="k">typename</span> <span class="n">value_type</span> <span class="o">=</span> <span class="n">axis</span><span class="o">&lt;</span><span class="mi">0</span><span class="o">&gt;::</span><span class="n">type</span><span class="p">;</span>
 102
 103     <span class="k">const</span> <span class="n">value_type</span><span class="o">&amp;</span> <span class="k">operator</span><span class="p">[](</span><span class="k">const</span> <span class="n">T</span><span class="o">&amp;</span><span class="p">,</span> <span class="kt">size_t</span> <span class="n">i</span><span class="p">);</span>
 104         <span class="n">value_type</span><span class="o">&amp;</span> <span class="k">operator</span><span class="p">[](</span>      <span class="n">T</span><span class="o">&amp;</span><span class="p">,</span> <span class="kt">size_t</span> <span class="n">i</span><span class="p">);</span>
 105
 106     <span class="n">value_type</span> <span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">;</span>
 107 <span class="p">};</span>
 108 </pre></div>
 109 </div>
 110 <div class="admonition seealso">
 111 <p class="first admonition-title">See also</p>
 112 <ul class="last simple">
 113 <li><a class="reference external" href="reference/structboost_1_1gil_1_1_point_n_d_concept.html">PointNDConcept</a></li>
 114 <li><a class="reference external" href="reference/structboost_1_1gil_1_1_point2_d_concept.html">Point2DConcept</a></li>
 115 </ul>
 116 </div>
 117 </div>
 118 <div class="section" id="models">
 119 <h2><a class="toc-backref" href="#id2">Models</a></h2>
 120 <p>GIL provides a model of <code class="docutils literal"><span class="pre">Point2DConcept</span></code>, <code class="docutils literal"><span class="pre">point&lt;T&gt;</span></code> where <code class="docutils literal"><span class="pre">T</span></code> is the
 121 coordinate type.</p>
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