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| author | jpayne |
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| date | Tue, 18 Mar 2025 16:23:26 -0400 |
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| 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> | |
| 2 <html> | |
| 3 <head> | |
| 4 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> | |
| 5 <title>Surfaces: Cairo: A Vector Graphics Library</title> | |
| 6 <meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> | |
| 7 <link rel="home" href="index.html" title="Cairo: A Vector Graphics Library"> | |
| 8 <link rel="up" href="language-bindings.html" title="Appendix A. Creating a language binding for cairo"> | |
| 9 <link rel="prev" href="bindings-patterns.html" title="Patterns"> | |
| 10 <link rel="next" href="bindings-fonts.html" title="Fonts"> | |
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| 21 </tr></table> | |
| 22 <div class="sect1"> | |
| 23 <div class="titlepage"><div><div><h2 class="title" style="clear: both"> | |
| 24 <a name="bindings-surfaces"></a>Surfaces</h2></div></div></div> | |
| 25 <p> | |
| 26 Like patterns, surfaces, which use only the | |
| 27 <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> | |
| 28 type in the C API should be broken up into a hierarchy of types | |
| 29 in a language binding. | |
| 30 </p> | |
| 31 <pre class="programlisting"> | |
| 32 cairo_surface_t | |
| 33 cairo_image_surface_t | |
| 34 cairo_atsui_surface_t | |
| 35 cairo_win32_surface_t | |
| 36 cairo_xlib_surface_t | |
| 37 cairo_beos_surface_t | |
| 38 </pre> | |
| 39 <p> | |
| 40 Unlike patterns, the constructors and methods on these types are | |
| 41 clearly named, and can be trivially associated with the | |
| 42 appropriate subtype. Many language bindings will want to avoid | |
| 43 binding the platform-specific subtypes at all, since the | |
| 44 methods on these types are not useful without passing in native | |
| 45 C types. Unless there is a language binding for Xlib available, | |
| 46 there is no way to represent a XLib <span class="type">Display</span> * in | |
| 47 that language. | |
| 48 </p> | |
| 49 <p> | |
| 50 This doesn't mean that platform-specific surface types can't | |
| 51 be used in a language binding that doesn't bind the constructor. | |
| 52 A very common situation is to use a cairo language binding in | |
| 53 combination with a binding for a higher level system like | |
| 54 the <a class="ulink" href="http://www.gtk.org/" target="_top">GTK+</a> widget | |
| 55 toolkit. In such a situation, the higher level toolkit provides | |
| 56 ways to get references to platform specific surfaces. | |
| 57 </p> | |
| 58 <p> | |
| 59 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>, | |
| 60 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> | |
| 61 methods are provided for use in language bindings, and should | |
| 62 not be directly exposed to applications. One example of the use | |
| 63 of these functions in a language binding is creating a binding for: | |
| 64 </p> | |
| 65 <pre class="programlisting"> | |
| 66 cairo_surface_t * | |
| 67 <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, | |
| 68 cairo_format_t format, | |
| 69 int width, | |
| 70 int height, | |
| 71 int stride); | |
| 72 </pre> | |
| 73 <p> | |
| 74 The memory block passed in for <em class="parameter"><code>data</code></em> must be | |
| 75 kept around until the surface is destroyed, so the language | |
| 76 binding must have some way of determining when that happens. The | |
| 77 way to do this is to use the <em class="parameter"><code>destroy</code></em> | |
| 78 argument to <code class="function">cairo_surface_set_user_data()</code>. | |
| 79 </p> | |
| 80 <p class="remark"><em><span class="remark"> | |
| 81 Some languages may not have a suitable “pointer to a block of | |
| 82 data” type to pass in for <em class="parameter"><code>data</code></em>. And even | |
| 83 where a language does have such a type, the user will be | |
| 84 frequently able to cause the backing store to be reallocated | |
| 85 to a different location or truncated. Should we recommend a | |
| 86 standard type name and binding for a buffer object here? | |
| 87 </span></em></p> | |
| 88 </div> | |
| 89 <div class="footer"> | |
| 90 <hr>Generated by GTK-Doc V1.27</div> | |
| 91 </body> | |
| 92 </html> |