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5 <title>Overloading and optional arguments: Cairo: A Vector Graphics Library</title>
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7 <link rel="home" href="index.html" title="Cairo: A Vector Graphics Library">
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8 <link rel="up" href="language-bindings.html" title="Appendix A. Creating a language binding for cairo">
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21 </tr></table>
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22 <div class="sect1">
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23 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
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24 <a name="bindings-overloading"></a>Overloading and optional arguments</h2></div></div></div>
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25 <p>
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26 Function overloading (having a several variants of a function
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27 with the same name and different arguments) is a language
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28 feature available in many languages but not in C.
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29 </p>
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30 <p>
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31 In general, language binding authors should use restraint in
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32 combining functions in the cairo API via function
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33 overloading. What may seem like an obvious overload now may
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34 turn out to be strange with future additions to cairo.
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35 It might seem logical to make
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36 <a class="link" href="cairo-cairo-t.html#cairo-set-source-rgb" title="cairo_set_source_rgb ()"><code class="function">cairo_set_source_rgb()</code></a>
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37 an overload of <code class="function">cairo_set_source()</code>, but future plans to add
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38 <code class="function">cairo_set_source_rgb_premultiplied()</code>,
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39 which will also take three doubles make this a bad idea. For
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40 this reason, only the following pairs of functions should
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41 be combined via overloading
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42 </p>
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43 <pre class="programlisting">
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44 void
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45 cairo_set_source (cairo_t *cr, cairo_pattern_t *source);
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46
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47 void
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48 cairo_set_source_surface (cairo_t *cr,
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49 cairo_surface_t *source,
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50 double surface_x,
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51 double surface_y);
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52
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53 void
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54 cairo_mask (cairo_t *cr,
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55 cairo_pattern_t *pattern);
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56
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57 void
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58 cairo_mask_surface (cairo_t *cr,
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59 cairo_surface_t *surface,
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60 double surface_x,
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61 double surface_y);
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62
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63 cairo_surface_t *
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64 cairo_image_surface_create (cairo_format_t format,
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65 int width,
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66 int height);
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67 cairo_surface_t *
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68 cairo_image_surface_create_for_data (unsigned char *data,
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69 cairo_format_t format,
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70 int width,
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71 int height,
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72 int stride);
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73
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74 cairo_status_t
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75 cairo_surface_write_to_png (cairo_surface_t *surface,
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76 const char *filename);
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77
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78 cairo_status_t
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79 cairo_surface_write_to_png_stream (cairo_surface_t *surface,
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80 cairo_write_func_t write_func,
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81 void *closure);
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82
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83 cairo_surface_t *
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84 cairo_image_surface_create_from_png (const char *filename);
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85
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86 cairo_surface_t *
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87 cairo_image_surface_create_from_png_stream (cairo_read_func_t read_func,
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88 void *closure);
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89 </pre>
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90 <p>
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91 Note that there are cases where all constructors for a type
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92 aren't overloaded together. For example
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93 <a class="link" href="cairo-PNG-Support.html#cairo-image-surface-create-from-png" title="cairo_image_surface_create_from_png ()"><code class="function">cairo_image_surface_create_from_png()</code></a>
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94 should <span class="emphasis"><em>not</em></span> be overloaded together with
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95 <a class="link" href="cairo-Image-Surfaces.html#cairo-image-surface-create" title="cairo_image_surface_create ()"><code class="function">cairo_image_surface_create()</code></a>.
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96 In such cases, the remaining constructors will typically need to
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97 be bound as static methods. In Java, for example, we might have:
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98 </p>
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99 <pre class="programlisting">
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100 Surface surface1 = ImageSurface(Format.RGB24, 100, 100);
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101 Surface surface2 = ImageSurface.createFromPNG("camera.png");</pre>
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102 <p>
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103 Some other overloads that add combinations not found in C may be
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104 convenient for users for language bindings that provide
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105 <span class="type">cairo_point_t</span> and <span class="type">cairo_rectangle_t</span>
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106 types, for example:
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107 </p>
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108 <pre class="programlisting">
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109 void
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110 cairo_move_to (cairo_t *cr,
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111 cairo_point_t *point);
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112 void
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113 cairo_rectangle (cairo_t *cr,
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114 cairo_rectangle_t *rectangle);
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115 </pre>
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116 </div>
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117 <div class="footer">
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120 </html> |
