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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>PNG Support: Cairo: A Vector Graphics Library</title> <meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> <link rel="home" href="index.html" title="Cairo: A Vector Graphics Library"> <link rel="up" href="cairo-surfaces.html" title="Surfaces"> <link rel="prev" href="cairo-PDF-Surfaces.html" title="PDF Surfaces"> <link rel="next" href="cairo-PostScript-Surfaces.html" title="PostScript Surfaces"> <meta name="generator" content="GTK-Doc V1.25 (XML mode)"> <link rel="stylesheet" href="style.css" type="text/css"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table class="navigation" id="top" width="100%" summary="Navigation header" cellpadding="2" cellspacing="5"><tr valign="middle"> <td width="100%" align="left" class="shortcuts"> <a href="#" class="shortcut">Top</a><span id="nav_description"> <span class="dim">|</span> <a href="#cairo-PNG-Support.description" class="shortcut">Description</a></span> </td> <td><a accesskey="h" href="index.html"><img src="home.png" width="16" height="16" border="0" alt="Home"></a></td> <td><a accesskey="u" href="cairo-surfaces.html"><img src="up.png" width="16" height="16" border="0" alt="Up"></a></td> <td><a accesskey="p" href="cairo-PDF-Surfaces.html"><img src="left.png" width="16" height="16" border="0" alt="Prev"></a></td> <td><a accesskey="n" href="cairo-PostScript-Surfaces.html"><img src="right.png" width="16" height="16" border="0" alt="Next"></a></td> </tr></table> <div class="refentry"> <a name="cairo-PNG-Support"></a><div class="titlepage"></div> <div class="refnamediv"><table width="100%"><tr> <td valign="top"> <h2><span class="refentrytitle"><a name="cairo-PNG-Support.top_of_page"></a>PNG Support</span></h2> <p>PNG Support — Reading and writing PNG images</p> </td> <td class="gallery_image" valign="top" align="right"></td> </tr></table></div> <div class="refsect1"> <a name="cairo-PNG-Support.functions"></a><h2>Functions</h2> <div class="informaltable"><table class="informaltable" width="100%" border="0"> <colgroup> <col width="150px" class="functions_return"> <col class="functions_name"> </colgroup> <tbody> <tr> <td class="function_type"> <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="returnvalue">cairo_surface_t</span></a> * </td> <td class="function_name"> <a class="link" href="cairo-PNG-Support.html#cairo-image-surface-create-from-png" title="cairo_image_surface_create_from_png ()">cairo_image_surface_create_from_png</a> <span class="c_punctuation">()</span> </td> </tr> <tr> <td class="function_type"> <a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a> </td> <td class="function_name"> <span class="c_punctuation">(</span><a class="link" href="cairo-PNG-Support.html#cairo-read-func-t" title="cairo_read_func_t ()">*cairo_read_func_t</a><span class="c_punctuation">)</span> <span class="c_punctuation">()</span> </td> </tr> <tr> <td class="function_type"> <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="returnvalue">cairo_surface_t</span></a> * </td> <td class="function_name"> <a class="link" href="cairo-PNG-Support.html#cairo-image-surface-create-from-png-stream" title="cairo_image_surface_create_from_png_stream ()">cairo_image_surface_create_from_png_stream</a> <span class="c_punctuation">()</span> </td> </tr> <tr> <td class="function_type"> <a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a> </td> <td class="function_name"> <a class="link" href="cairo-PNG-Support.html#cairo-surface-write-to-png" title="cairo_surface_write_to_png ()">cairo_surface_write_to_png</a> <span class="c_punctuation">()</span> </td> </tr> <tr> <td class="function_type"> <a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a> </td> <td class="function_name"> <span class="c_punctuation">(</span><a class="link" href="cairo-PNG-Support.html#cairo-write-func-t" title="cairo_write_func_t ()">*cairo_write_func_t</a><span class="c_punctuation">)</span> <span class="c_punctuation">()</span> </td> </tr> <tr> <td class="function_type"> <a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a> </td> <td class="function_name"> <a class="link" href="cairo-PNG-Support.html#cairo-surface-write-to-png-stream" title="cairo_surface_write_to_png_stream ()">cairo_surface_write_to_png_stream</a> <span class="c_punctuation">()</span> </td> </tr> </tbody> </table></div> </div> <div class="refsect1"> <a name="cairo-PNG-Support.other"></a><h2>Types and Values</h2> <div class="informaltable"><table class="informaltable" width="100%" border="0"> <colgroup> <col width="150px" class="name"> <col class="description"> </colgroup> <tbody><tr> <td class="define_keyword">#define</td> <td class="function_name"><a class="link" href="cairo-PNG-Support.html#CAIRO-HAS-PNG-FUNCTIONS:CAPS" title="CAIRO_HAS_PNG_FUNCTIONS">CAIRO_HAS_PNG_FUNCTIONS</a></td> </tr></tbody> </table></div> </div> <div class="refsect1"> <a name="cairo-PNG-Support.description"></a><h2>Description</h2> <p>The PNG functions allow reading PNG images into image surfaces, and writing any surface to a PNG file.</p> <p>It is a toy API. It only offers very simple support for reading and writing PNG files, which is sufficient for testing and demonstration purposes. Applications which need more control over the generated PNG file should access the pixel data directly, using <a class="link" href="cairo-Image-Surfaces.html#cairo-image-surface-get-data" title="cairo_image_surface_get_data ()"><code class="function">cairo_image_surface_get_data()</code></a> or a backend-specific access function, and process it with another library, e.g. gdk-pixbuf or libpng.</p> </div> <div class="refsect1"> <a name="cairo-PNG-Support.functions_details"></a><h2>Functions</h2> <div class="refsect2"> <a name="cairo-image-surface-create-from-png"></a><h3>cairo_image_surface_create_from_png ()</h3> <pre class="programlisting"><a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="returnvalue">cairo_surface_t</span></a> * cairo_image_surface_create_from_png (<em class="parameter"><code>const <span class="type">char</span> *filename</code></em>);</pre> <p>Creates a new image surface and initializes the contents to the given PNG file.</p> <div class="refsect3"> <a name="cairo-image-surface-create-from-png.parameters"></a><h4>Parameters</h4> <div class="informaltable"><table class="informaltable" width="100%" border="0"> <colgroup> <col width="150px" class="parameters_name"> <col class="parameters_description"> <col width="200px" class="parameters_annotations"> </colgroup> <tbody><tr> <td class="parameter_name"><p>filename</p></td> <td class="parameter_description"><p>name of PNG file to load. On Windows this filename is encoded in UTF-8.</p></td> <td class="parameter_annotations"> </td> </tr></tbody> </table></div> </div> <div class="refsect3"> <a name="cairo-image-surface-create-from-png.returns"></a><h4>Returns</h4> <p> a new <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> initialized with the contents of the PNG file, or a "nil" surface if any error occurred. A nil surface can be checked for with cairo_surface_status(surface) which may return one of the following values:</p> <p><a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-NO-MEMORY:CAPS"><code class="literal">CAIRO_STATUS_NO_MEMORY</code></a> <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-FILE-NOT-FOUND:CAPS"><code class="literal">CAIRO_STATUS_FILE_NOT_FOUND</code></a> <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-READ-ERROR:CAPS"><code class="literal">CAIRO_STATUS_READ_ERROR</code></a> <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-PNG-ERROR:CAPS"><code class="literal">CAIRO_STATUS_PNG_ERROR</code></a></p> <p>Alternatively, you can allow errors to propagate through the drawing operations and check the status on the context upon completion using <a class="link" href="cairo-cairo-t.html#cairo-status" title="cairo_status ()"><code class="function">cairo_status()</code></a>.</p> </div> <p class="since">Since: 1.0</p> </div> <hr> <div class="refsect2"> <a name="cairo-read-func-t"></a><h3>cairo_read_func_t ()</h3> <pre class="programlisting"><a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a> <span class="c_punctuation">(</span>*cairo_read_func_t<span class="c_punctuation">)</span> (<em class="parameter"><code><span class="type">void</span> *closure</code></em>, <em class="parameter"><code>unsigned <span class="type">char</span> *data</code></em>, <em class="parameter"><code>unsigned <span class="type">int</span> length</code></em>);</pre> <p><a class="link" href="cairo-PNG-Support.html#cairo-read-func-t" title="cairo_read_func_t ()"><span class="type">cairo_read_func_t</span></a> is the type of function which is called when a backend needs to read data from an input stream. It is passed the closure which was specified by the user at the time the read function was registered, the buffer to read the data into and the length of the data in bytes. The read function should return <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-SUCCESS:CAPS"><code class="literal">CAIRO_STATUS_SUCCESS</code></a> if all the data was successfully read, <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-READ-ERROR:CAPS"><code class="literal">CAIRO_STATUS_READ_ERROR</code></a> otherwise.</p> <div class="refsect3"> <a name="cairo-read-func-t.parameters"></a><h4>Parameters</h4> <div class="informaltable"><table class="informaltable" width="100%" border="0"> <colgroup> <col width="150px" class="parameters_name"> <col class="parameters_description"> <col width="200px" class="parameters_annotations"> </colgroup> <tbody> <tr> <td class="parameter_name"><p>closure</p></td> <td class="parameter_description"><p>the input closure</p></td> <td class="parameter_annotations"> </td> </tr> <tr> <td class="parameter_name"><p>data</p></td> <td class="parameter_description"><p>the buffer into which to read the data</p></td> <td class="parameter_annotations"> </td> </tr> <tr> <td class="parameter_name"><p>length</p></td> <td class="parameter_description"><p>the amount of data to read</p></td> <td class="parameter_annotations"> </td> </tr> </tbody> </table></div> </div> <div class="refsect3"> <a name="cairo-read-func-t.returns"></a><h4>Returns</h4> <p> the status code of the read operation</p> </div> <p class="since">Since: 1.0</p> </div> <hr> <div class="refsect2"> <a name="cairo-image-surface-create-from-png-stream"></a><h3>cairo_image_surface_create_from_png_stream ()</h3> <pre class="programlisting"><a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="returnvalue">cairo_surface_t</span></a> * cairo_image_surface_create_from_png_stream (<em class="parameter"><code><a class="link" href="cairo-PNG-Support.html#cairo-read-func-t" title="cairo_read_func_t ()"><span class="type">cairo_read_func_t</span></a> read_func</code></em>, <em class="parameter"><code><span class="type">void</span> *closure</code></em>);</pre> <p>Creates a new image surface from PNG data read incrementally via the <em class="parameter"><code>read_func</code></em> function.</p> <div class="refsect3"> <a name="cairo-image-surface-create-from-png-stream.parameters"></a><h4>Parameters</h4> <div class="informaltable"><table class="informaltable" width="100%" border="0"> <colgroup> <col width="150px" class="parameters_name"> <col class="parameters_description"> <col width="200px" class="parameters_annotations"> </colgroup> <tbody> <tr> <td class="parameter_name"><p>read_func</p></td> <td class="parameter_description"><p>function called to read the data of the file</p></td> <td class="parameter_annotations"> </td> </tr> <tr> <td class="parameter_name"><p>closure</p></td> <td class="parameter_description"><p>data to pass to <em class="parameter"><code>read_func</code></em> .</p></td> <td class="parameter_annotations"> </td> </tr> </tbody> </table></div> </div> <div class="refsect3"> <a name="cairo-image-surface-create-from-png-stream.returns"></a><h4>Returns</h4> <p> a new <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> initialized with the contents of the PNG file or a "nil" surface if the data read is not a valid PNG image or memory could not be allocated for the operation. A nil surface can be checked for with cairo_surface_status(surface) which may return one of the following values:</p> <p><a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-NO-MEMORY:CAPS"><code class="literal">CAIRO_STATUS_NO_MEMORY</code></a> <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-READ-ERROR:CAPS"><code class="literal">CAIRO_STATUS_READ_ERROR</code></a> <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-PNG-ERROR:CAPS"><code class="literal">CAIRO_STATUS_PNG_ERROR</code></a></p> <p>Alternatively, you can allow errors to propagate through the drawing operations and check the status on the context upon completion using <a class="link" href="cairo-cairo-t.html#cairo-status" title="cairo_status ()"><code class="function">cairo_status()</code></a>.</p> </div> <p class="since">Since: 1.0</p> </div> <hr> <div class="refsect2"> <a name="cairo-surface-write-to-png"></a><h3>cairo_surface_write_to_png ()</h3> <pre class="programlisting"><a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a> cairo_surface_write_to_png (<em class="parameter"><code><a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> *surface</code></em>, <em class="parameter"><code>const <span class="type">char</span> *filename</code></em>);</pre> <p>Writes the contents of <em class="parameter"><code>surface</code></em> to a new file <em class="parameter"><code>filename</code></em> as a PNG image.</p> <div class="refsect3"> <a name="cairo-surface-write-to-png.parameters"></a><h4>Parameters</h4> <div class="informaltable"><table class="informaltable" width="100%" border="0"> <colgroup> <col width="150px" class="parameters_name"> <col class="parameters_description"> <col width="200px" class="parameters_annotations"> </colgroup> <tbody> <tr> <td class="parameter_name"><p>surface</p></td> <td class="parameter_description"><p>a <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> with pixel contents</p></td> <td class="parameter_annotations"> </td> </tr> <tr> <td class="parameter_name"><p>filename</p></td> <td class="parameter_description"><p>the name of a file to write to; on Windows this filename is encoded in UTF-8.</p></td> <td class="parameter_annotations"> </td> </tr> </tbody> </table></div> </div> <div class="refsect3"> <a name="cairo-surface-write-to-png.returns"></a><h4>Returns</h4> <p> <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-SUCCESS:CAPS"><code class="literal">CAIRO_STATUS_SUCCESS</code></a> if the PNG file was written successfully. Otherwise, <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-NO-MEMORY:CAPS"><code class="literal">CAIRO_STATUS_NO_MEMORY</code></a> if memory could not be allocated for the operation or <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-SURFACE-TYPE-MISMATCH:CAPS"><code class="literal">CAIRO_STATUS_SURFACE_TYPE_MISMATCH</code></a> if the surface does not have pixel contents, or <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-WRITE-ERROR:CAPS"><code class="literal">CAIRO_STATUS_WRITE_ERROR</code></a> if an I/O error occurs while attempting to write the file, or <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-PNG-ERROR:CAPS"><code class="literal">CAIRO_STATUS_PNG_ERROR</code></a> if libpng returned an error.</p> </div> <p class="since">Since: 1.0</p> </div> <hr> <div class="refsect2"> <a name="cairo-write-func-t"></a><h3>cairo_write_func_t ()</h3> <pre class="programlisting"><a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a> <span class="c_punctuation">(</span>*cairo_write_func_t<span class="c_punctuation">)</span> (<em class="parameter"><code><span class="type">void</span> *closure</code></em>, <em class="parameter"><code>const unsigned <span class="type">char</span> *data</code></em>, <em class="parameter"><code>unsigned <span class="type">int</span> length</code></em>);</pre> <p><a class="link" href="cairo-PNG-Support.html#cairo-write-func-t" title="cairo_write_func_t ()"><span class="type">cairo_write_func_t</span></a> is the type of function which is called when a backend needs to write data to an output stream. It is passed the closure which was specified by the user at the time the write function was registered, the data to write and the length of the data in bytes. The write function should return <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-SUCCESS:CAPS"><code class="literal">CAIRO_STATUS_SUCCESS</code></a> if all the data was successfully written, <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-WRITE-ERROR:CAPS"><code class="literal">CAIRO_STATUS_WRITE_ERROR</code></a> otherwise.</p> <div class="refsect3"> <a name="cairo-write-func-t.parameters"></a><h4>Parameters</h4> <div class="informaltable"><table class="informaltable" width="100%" border="0"> <colgroup> <col width="150px" class="parameters_name"> <col class="parameters_description"> <col width="200px" class="parameters_annotations"> </colgroup> <tbody> <tr> <td class="parameter_name"><p>closure</p></td> <td class="parameter_description"><p>the output closure</p></td> <td class="parameter_annotations"> </td> </tr> <tr> <td class="parameter_name"><p>data</p></td> <td class="parameter_description"><p>the buffer containing the data to write</p></td> <td class="parameter_annotations"> </td> </tr> <tr> <td class="parameter_name"><p>length</p></td> <td class="parameter_description"><p>the amount of data to write</p></td> <td class="parameter_annotations"> </td> </tr> </tbody> </table></div> </div> <div class="refsect3"> <a name="cairo-write-func-t.returns"></a><h4>Returns</h4> <p> the status code of the write operation</p> </div> <p class="since">Since: 1.0</p> </div> <hr> <div class="refsect2"> <a name="cairo-surface-write-to-png-stream"></a><h3>cairo_surface_write_to_png_stream ()</h3> <pre class="programlisting"><a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a> cairo_surface_write_to_png_stream (<em class="parameter"><code><a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> *surface</code></em>, <em class="parameter"><code><a class="link" href="cairo-PNG-Support.html#cairo-write-func-t" title="cairo_write_func_t ()"><span class="type">cairo_write_func_t</span></a> write_func</code></em>, <em class="parameter"><code><span class="type">void</span> *closure</code></em>);</pre> <p>Writes the image surface to the write function.</p> <div class="refsect3"> <a name="cairo-surface-write-to-png-stream.parameters"></a><h4>Parameters</h4> <div class="informaltable"><table class="informaltable" width="100%" border="0"> <colgroup> <col width="150px" class="parameters_name"> <col class="parameters_description"> <col width="200px" class="parameters_annotations"> </colgroup> <tbody> <tr> <td class="parameter_name"><p>surface</p></td> <td class="parameter_description"><p>a <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> with pixel contents</p></td> <td class="parameter_annotations"> </td> </tr> <tr> <td class="parameter_name"><p>write_func</p></td> <td class="parameter_description"><p>a <a class="link" href="cairo-PNG-Support.html#cairo-write-func-t" title="cairo_write_func_t ()"><span class="type">cairo_write_func_t</span></a></p></td> <td class="parameter_annotations"> </td> </tr> <tr> <td class="parameter_name"><p>closure</p></td> <td class="parameter_description"><p>closure data for the write function</p></td> <td class="parameter_annotations"> </td> </tr> </tbody> </table></div> </div> <div class="refsect3"> <a name="cairo-surface-write-to-png-stream.returns"></a><h4>Returns</h4> <p> <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-SUCCESS:CAPS"><code class="literal">CAIRO_STATUS_SUCCESS</code></a> if the PNG file was written successfully. Otherwise, <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-NO-MEMORY:CAPS"><code class="literal">CAIRO_STATUS_NO_MEMORY</code></a> is returned if memory could not be allocated for the operation, <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-SURFACE-TYPE-MISMATCH:CAPS"><code class="literal">CAIRO_STATUS_SURFACE_TYPE_MISMATCH</code></a> if the surface does not have pixel contents, or <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-PNG-ERROR:CAPS"><code class="literal">CAIRO_STATUS_PNG_ERROR</code></a> if libpng returned an error.</p> </div> <p class="since">Since: 1.0</p> </div> </div> <div class="refsect1"> <a name="cairo-PNG-Support.other_details"></a><h2>Types and Values</h2> <div class="refsect2"> <a name="CAIRO-HAS-PNG-FUNCTIONS:CAPS"></a><h3>CAIRO_HAS_PNG_FUNCTIONS</h3> <pre class="programlisting">#define CAIRO_HAS_PNG_FUNCTIONS 1 </pre> <p>Defined if the PNG functions are available. This macro can be used to conditionally compile code using the cairo PNG functions.</p> <p class="since">Since: 1.0</p> </div> </div> <div class="refsect1"> <a name="cairo-PNG-Support.see-also"></a><h2>See Also</h2> <p><a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a></p> </div> </div> <div class="footer"> <hr>Generated by GTK-Doc V1.25</div> </body> </html>