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- <div class="section" id="metafunctions">
- <h1>Metafunctions</h1>
- <div class="contents local topic" id="contents">
- <ul class="simple">
- <li><a class="reference internal" href="#overview" id="id1">Overview</a></li>
- <li><a class="reference internal" href="#homogeneous-memory-based-images" id="id2">Homogeneous memory-based images</a></li>
- <li><a class="reference internal" href="#packed-and-bit-aligned-images" id="id3">Packed and bit-aligned images</a></li>
- <li><a class="reference internal" href="#iterators-and-views" id="id4">Iterators and views</a></li>
- <li><a class="reference internal" href="#pixel-components" id="id5">Pixel components</a></li>
- <li><a class="reference internal" href="#deriving-and-manipulating-existing-types" id="id6">Deriving and manipulating existing types</a></li>
- <li><a class="reference internal" href="#type-traits" id="id7">Type traits</a></li>
- </ul>
- </div>
- <div class="section" id="overview">
- <h2><a class="toc-backref" href="#id1">Overview</a></h2>
- <p>Flexibility comes at a price. GIL types can be very long and hard to read.
- To address this problem, GIL provides typedefs to refer to any standard image,
- pixel iterator, pixel locator, pixel reference or pixel value.</p>
- <p>They follow this pattern:</p>
- <div class="highlight-c++"><div class="highlight"><pre><span class="o">*</span><span class="n">ColorSpace</span><span class="o">*</span> <span class="o">+</span> <span class="o">*</span><span class="n">BitDepth</span><span class="o">*</span> <span class="o">+</span> <span class="p">[</span><span class="s">"s|f"</span><span class="p">]</span> <span class="o">+</span> <span class="p">[</span><span class="s">"c"</span><span class="p">]</span> <span class="o">+</span> <span class="p">[</span><span class="s">"_planar"</span><span class="p">]</span> <span class="o">+</span> <span class="p">[</span><span class="s">"_step"</span><span class="p">]</span> <span class="o">+</span> <span class="o">*</span><span class="n">ClassType</span><span class="o">*</span> <span class="o">+</span> <span class="s">"_t"</span>
- </pre></div>
- </div>
- <p>where <em>ColorSpace</em> also indicates the ordering of components.</p>
- <p>Examples are <code class="docutils literal"><span class="pre">rgb</span></code>, <code class="docutils literal"><span class="pre">bgr</span></code>, <code class="docutils literal"><span class="pre">cmyk</span></code>, <code class="docutils literal"><span class="pre">rgba</span></code>. <em>BitDepth</em> can be, for
- example, <code class="docutils literal"><span class="pre">8</span></code>,``16``,``32``. By default the bits are unsigned integral type.
- Append <code class="docutils literal"><span class="pre">s</span></code> to the bit depth to indicate signed integral, or <code class="docutils literal"><span class="pre">f</span></code> to
- indicate floating point. <code class="docutils literal"><span class="pre">c</span></code> indicates object whose associated pixel
- reference is immutable. <code class="docutils literal"><span class="pre">_planar</span></code> indicates planar organization (as opposed
- to interleaved). <code class="docutils literal"><span class="pre">_step</span></code> indicates the type has a dynamic step and
- <em>ClassType</em> is <code class="docutils literal"><span class="pre">_image</span></code> (image, using a standard allocator), <code class="docutils literal"><span class="pre">_view</span></code>
- (image view), <code class="docutils literal"><span class="pre">_loc</span></code> (pixel locator), <code class="docutils literal"><span class="pre">_ptr</span></code> (pixel iterator), <code class="docutils literal"><span class="pre">_ref</span></code>
- (pixel reference), <code class="docutils literal"><span class="pre">_pixel</span></code> (pixel value).</p>
- <p>Here are examples:</p>
- <div class="highlight-cpp"><div class="highlight"><pre><span class="n">bgr8_image_t</span> <span class="n">i</span><span class="p">;</span> <span class="c1">// 8-bit unsigned (unsigned char) interleaved BGR image</span>
- <span class="n">cmyk16_pixel_t</span><span class="p">;</span> <span class="n">x</span><span class="p">;</span> <span class="c1">// 16-bit unsigned (unsigned short) CMYK pixel value;</span>
- <span class="n">cmyk16sc_planar_ref_t</span> <span class="nf">p</span><span class="p">(</span><span class="n">x</span><span class="p">);</span> <span class="c1">// const reference to a 16-bit signed integral (signed short) planar CMYK pixel x.</span>
- <span class="n">rgb32f_planar_step_ptr_t</span> <span class="n">ii</span><span class="p">;</span> <span class="c1">// step iterator to a floating point 32-bit (float) planar RGB pixel.</span>
- </pre></div>
- </div>
- </div>
- <div class="section" id="homogeneous-memory-based-images">
- <h2><a class="toc-backref" href="#id2">Homogeneous memory-based images</a></h2>
- <p>GIL provides the metafunctions that return the types of standard
- homogeneous memory-based GIL constructs given a channel type, a
- layout, and whether the construct is planar, has a step along the X
- direction, and is mutable:</p>
- <div class="highlight-cpp"><div class="highlight"><pre><span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">ChannelValue</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsPlanar</span><span class="o">=</span><span class="nb">false</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsMutable</span><span class="o">=</span><span class="nb">true</span><span class="o">></span>
- <span class="k">struct</span> <span class="n">pixel_reference_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">Channel</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Layout</span><span class="o">></span>
- <span class="k">struct</span> <span class="n">pixel_value_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">ChannelValue</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsPlanar</span><span class="o">=</span><span class="nb">false</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsStep</span><span class="o">=</span><span class="nb">false</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsMutable</span><span class="o">=</span><span class="nb">true</span><span class="o">></span>
- <span class="k">struct</span> <span class="n">iterator_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">ChannelValue</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsPlanar</span><span class="o">=</span><span class="nb">false</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsXStep</span><span class="o">=</span><span class="nb">false</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsMutable</span><span class="o">=</span><span class="nb">true</span><span class="o">></span>
- <span class="k">struct</span> <span class="n">locator_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">ChannelValue</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsPlanar</span><span class="o">=</span><span class="nb">false</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsXStep</span><span class="o">=</span><span class="nb">false</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsMutable</span><span class="o">=</span><span class="nb">true</span><span class="o">></span>
- <span class="k">struct</span> <span class="n">view_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">ChannelValue</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsPlanar</span><span class="o">=</span><span class="nb">false</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">image_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">BitField</span><span class="p">,</span> <span class="k">typename</span> <span class="n">ChannelBitSizeVector</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">packed_image_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">ChannelBitSizeVector</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">bit_aligned_image_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- </pre></div>
- </div>
- </div>
- <div class="section" id="packed-and-bit-aligned-images">
- <h2><a class="toc-backref" href="#id3">Packed and bit-aligned images</a></h2>
- <p>There are also helper metafunctions to construct packed and
- bit-aligned images with up to five channels:</p>
- <div class="highlight-cpp"><div class="highlight"><pre><span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">BitField</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size1</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">packed_image1_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">BitField</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size1</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size2</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">packed_image2_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">BitField</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size1</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size2</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size3</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">packed_image3_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">BitField</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size1</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size2</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size3</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size4</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">packed_image4_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">BitField</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size1</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size2</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size3</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size4</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size5</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">packed_image5_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="kt">unsigned</span> <span class="n">Size1</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">bit_aligned_image1_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="kt">unsigned</span> <span class="n">Size1</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size2</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">bit_aligned_image2_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="kt">unsigned</span> <span class="n">Size1</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size2</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size3</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">bit_aligned_image3_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="kt">unsigned</span> <span class="n">Size1</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size2</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size3</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size4</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">bit_aligned_image4_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="kt">unsigned</span> <span class="n">Size1</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size2</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size3</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size4</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="n">Size5</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Alloc</span><span class="o">=</span><span class="n">std</span><span class="o">::</span><span class="n">allocator</span><span class="o"><</span><span class="kt">unsigned</span> <span class="kt">char</span><span class="o">></span> <span class="o">></span>
- <span class="k">struct</span> <span class="n">bit_aligned_image5_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- </pre></div>
- </div>
- </div>
- <div class="section" id="iterators-and-views">
- <h2><a class="toc-backref" href="#id4">Iterators and views</a></h2>
- <p>Here <code class="docutils literal"><span class="pre">ChannelValue</span></code> models <code class="docutils literal"><span class="pre">ChannelValueConcept</span></code>. We don’t need
- <code class="docutils literal"><span class="pre">IsYStep</span></code> because GIL’s memory-based locator and view already allow
- the vertical step to be specified dynamically. Iterators and views can
- be constructed from a pixel type:</p>
- <div class="highlight-cpp"><div class="highlight"><pre><span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">Pixel</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsPlanar</span><span class="o">=</span><span class="nb">false</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsStep</span><span class="o">=</span><span class="nb">false</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsMutable</span><span class="o">=</span><span class="nb">true</span><span class="o">></span>
- <span class="k">struct</span> <span class="n">iterator_type_from_pixel</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">Pixel</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsPlanar</span><span class="o">=</span><span class="nb">false</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsStepX</span><span class="o">=</span><span class="nb">false</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">IsMutable</span><span class="o">=</span><span class="nb">true</span><span class="o">></span>
- <span class="k">struct</span> <span class="n">view_type_from_pixel</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- </pre></div>
- </div>
- <p>Using a heterogeneous pixel type will result in heterogeneous iterators and
- views. Types can also be constructed from horizontal iterator:</p>
- <div class="highlight-cpp"><div class="highlight"><pre><span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">XIterator</span><span class="o">></span>
- <span class="k">struct</span> <span class="n">type_from_x_iterator</span>
- <span class="p">{</span>
- <span class="k">typedef</span> <span class="p">...</span> <span class="n">step_iterator_t</span><span class="p">;</span>
- <span class="k">typedef</span> <span class="p">...</span> <span class="n">xy_locator_t</span><span class="p">;</span>
- <span class="k">typedef</span> <span class="p">...</span> <span class="n">view_t</span><span class="p">;</span>
- <span class="p">};</span>
- </pre></div>
- </div>
- </div>
- <div class="section" id="pixel-components">
- <h2><a class="toc-backref" href="#id5">Pixel components</a></h2>
- <p>You can get pixel-related types of any pixel-based GIL constructs (pixels,
- iterators, locators and views) using the following metafunctions provided by
- <code class="docutils literal"><span class="pre">PixelBasedConcept</span></code>, <code class="docutils literal"><span class="pre">HomogeneousPixelBasedConcept</span></code> and metafunctions
- built on top of them:</p>
- <div class="highlight-cpp"><div class="highlight"><pre><span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">T</span><span class="o">></span> <span class="k">struct</span> <span class="n">color_space_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">T</span><span class="o">></span> <span class="k">struct</span> <span class="n">channel_mapping_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">T</span><span class="o">></span> <span class="k">struct</span> <span class="n">is_planar</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="c1">// Defined by homogeneous constructs</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">T</span><span class="o">></span> <span class="k">struct</span> <span class="n">channel_type</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">T</span><span class="o">></span> <span class="k">struct</span> <span class="n">num_channels</span> <span class="p">{</span> <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="p">};</span>
- </pre></div>
- </div>
- </div>
- <div class="section" id="deriving-and-manipulating-existing-types">
- <h2><a class="toc-backref" href="#id6">Deriving and manipulating existing types</a></h2>
- <p>There are metafunctions to construct the type of a construct from an existing
- type by changing one or more of its properties:</p>
- <div class="highlight-cpp"><div class="highlight"><pre><span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">PixelReference</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">ChannelValue</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">IsPlanar</span><span class="p">,</span> <span class="k">typename</span> <span class="n">IsMutable</span><span class="o">></span>
- <span class="k">struct</span> <span class="n">derived_pixel_reference_type</span>
- <span class="p">{</span>
- <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="c1">// Models PixelConcept</span>
- <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">Iterator</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">ChannelValue</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">IsPlanar</span><span class="p">,</span> <span class="k">typename</span> <span class="n">IsStep</span><span class="p">,</span> <span class="k">typename</span> <span class="n">IsMutable</span><span class="o">></span>
- <span class="k">struct</span> <span class="n">derived_iterator_type</span>
- <span class="p">{</span>
- <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="c1">// Models PixelIteratorConcept</span>
- <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">View</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">ChannelValue</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">IsPlanar</span><span class="p">,</span> <span class="k">typename</span> <span class="n">IsXStep</span><span class="p">,</span> <span class="k">typename</span> <span class="n">IsMutable</span><span class="o">></span>
- <span class="k">struct</span> <span class="n">derived_view_type</span>
- <span class="p">{</span>
- <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="c1">// Models ImageViewConcept</span>
- <span class="p">};</span>
- <span class="k">template</span> <span class="o"><</span><span class="k">typename</span> <span class="n">Image</span><span class="p">,</span>
- <span class="k">typename</span> <span class="n">ChannelValue</span><span class="p">,</span> <span class="k">typename</span> <span class="n">Layout</span><span class="p">,</span> <span class="k">typename</span> <span class="n">IsPlanar</span><span class="o">></span>
- <span class="k">struct</span> <span class="n">derived_image_type</span>
- <span class="p">{</span>
- <span class="k">typedef</span> <span class="p">...</span> <span class="n">type</span><span class="p">;</span> <span class="c1">// Models ImageConcept</span>
- <span class="p">};</span>
- </pre></div>
- </div>
- <p>You can replace one or more of its properties and use <code class="docutils literal"><span class="pre">boost::use_default</span></code>
- for the rest. In this case <code class="docutils literal"><span class="pre">IsPlanar</span></code>, <code class="docutils literal"><span class="pre">IsStep</span></code> and <code class="docutils literal"><span class="pre">IsMutable</span></code> are
- MPL boolean constants. For example, here is how to create the type of a view
- just like <code class="docutils literal"><span class="pre">View</span></code>, but being grayscale and planar:</p>
- <div class="highlight-cpp"><div class="highlight"><pre><span class="k">using</span> <span class="n">VT</span> <span class="o">=</span> <span class="k">typename</span> <span class="n">derived_view_type</span><span class="o"><</span><span class="n">View</span><span class="p">,</span> <span class="n">boost</span><span class="o">::</span><span class="n">use_default</span><span class="p">,</span> <span class="n">gray_t</span><span class="p">,</span> <span class="n">mpl</span><span class="o">::</span><span class="n">true_</span><span class="o">>::</span><span class="n">type</span><span class="p">;</span>
- </pre></div>
- </div>
- </div>
- <div class="section" id="type-traits">
- <h2><a class="toc-backref" href="#id7">Type traits</a></h2>
- <p>These are metafunctions, some of which return integral types which can be
- evaluated like this:</p>
- <div class="highlight-cpp"><div class="highlight"><pre><span class="k">static_assert</span><span class="p">(</span><span class="n">is_planar</span><span class="o"><</span><span class="n">rgb8_planar_view_t</span><span class="o">>::</span><span class="n">value</span> <span class="o">==</span> <span class="nb">true</span><span class="p">,</span> <span class="s">""</span><span class="p">);</span>
- </pre></div>
- </div>
- <p>GIL also supports type analysis metafunctions of the form:</p>
- <div class="highlight-cpp"><div class="highlight"><pre><span class="p">[</span><span class="n">pixel_reference</span><span class="o">/</span><span class="n">iterator</span><span class="o">/</span><span class="n">locator</span><span class="o">/</span><span class="n">view</span><span class="o">/</span><span class="n">image</span><span class="p">]</span> <span class="o">+</span> <span class="s">"_is_"</span> <span class="o">+</span> <span class="p">[</span><span class="n">basic</span><span class="o">/</span><span class="k">mutable</span><span class="o">/</span><span class="n">step</span><span class="p">]</span>
- </pre></div>
- </div>
- <p>For example:</p>
- <div class="highlight-cpp"><div class="highlight"><pre><span class="k">if</span> <span class="p">(</span><span class="n">view_is_mutable</span><span class="o"><</span><span class="n">View</span><span class="o">>::</span><span class="n">value</span><span class="p">)</span>
- <span class="p">{</span>
- <span class="p">...</span>
- <span class="p">}</span>
- </pre></div>
- </div>
- <p>A <em>basic</em> GIL construct is a memory-based construct that uses the built-in GIL
- classes and does not have any function object to invoke upon dereferencing.
- For example, a simple planar or interleaved, step or non-step RGB image view
- is basic, but a color converted view or a virtual view is not.</p>
- </div>
- </div>
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