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<title>Surfaces: Cairo: A Vector Graphics Library</title>
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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="bindings-surfaces"></a>Surfaces</h2></div></div></div>
<p>
      Like patterns, surfaces, which use only the
      <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a>
      type in the C API should be broken up into a hierarchy of types
      in a language binding.
    </p>
<pre class="programlisting">
cairo_surface_t
    cairo_image_surface_t
    cairo_atsui_surface_t
    cairo_win32_surface_t
    cairo_xlib_surface_t
    cairo_beos_surface_t
    </pre>
<p>
      Unlike patterns, the constructors and methods on these types are
      clearly named, and can be trivially associated with the
      appropriate subtype. Many language bindings will want to avoid
      binding the platform-specific subtypes at all, since the
      methods on these types are not useful without passing in native
      C types. Unless there is a language binding for Xlib available,
      there is no way to represent a XLib <span class="type">Display</span> * in
      that language.
    </p>
<p>
      This doesn't mean that platform-specific surface types can't
      be used in a language binding that doesn't bind the constructor.
      A very common situation is to use a cairo language binding in
      combination with a binding for a higher level system like
      the <a class="ulink" href="http://www.gtk.org/" target="_top">GTK+</a> widget
      toolkit. In such a situation, the higher level toolkit provides
      ways to get references to platform specific surfaces.
    </p>
<p>
      The <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-set-user-data" title="cairo_surface_set_user_data ()"><code class="function">cairo_surface_set_user_data()</code></a>,
      and <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-get-user-data" title="cairo_surface_get_user_data ()"><code class="function">cairo_surface_get_user_data()</code></a>
      methods are provided for use in language bindings, and should
      not be directly exposed to applications. One example of the use
      of these functions in a language binding is creating a binding for:
    </p>
<pre class="programlisting">
cairo_surface_t *
<a class="link" href="cairo-Image-Surfaces.html#cairo-image-surface-create-for-data" title="cairo_image_surface_create_for_data ()"><code class="function">cairo_image_surface_create_for_data</code></a> (unsigned char	       *data,
				     cairo_format_t		format,
				     int			width,
				     int			height,
				     int			stride);
</pre>
<p>
      The memory block passed in for <em class="parameter"><code>data</code></em> must be
      kept around until the surface is destroyed, so the language
      binding must have some way of determining when that happens. The
      way to do this is to use the <em class="parameter"><code>destroy</code></em>
      argument to <code class="function">cairo_surface_set_user_data()</code>.
    </p>
<p class="remark"><em><span class="remark">
      Some languages may not have a suitable “pointer to a block of
      data” type to pass in for <em class="parameter"><code>data</code></em>. And even
      where a language does have such a type, the user will be
      frequently able to cause the backing store to be reallocated
      to a different location or truncated. Should we recommend a
      standard type name and binding for a buffer object here?
    </span></em></p>
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author	jpayne
date	Tue, 18 Mar 2025 16:23:26 -0400
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