<?xml version='1.0' encoding='UTF-8'?> <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" [ <!ENTITY version SYSTEM "version.xml"> ]> <refentry id="cairo-PNG-Support"> <refmeta> <refentrytitle role="top_of_page" id="cairo-PNG-Support.top_of_page">PNG Support</refentrytitle> <manvolnum>3</manvolnum> <refmiscinfo> CAIRO Library </refmiscinfo> </refmeta> <refnamediv> <refname>PNG Support</refname> <refpurpose>Reading and writing PNG images</refpurpose> </refnamediv> <refsynopsisdiv id="cairo-PNG-Support.synopsis" role="synopsis"> <title role="synopsis.title">Synopsis</title> <synopsis>#define <link linkend="CAIRO-HAS-PNG-FUNCTIONS:CAPS">CAIRO_HAS_PNG_FUNCTIONS</link> <link linkend="cairo-surface-t"><returnvalue>cairo_surface_t</returnvalue></link> * <link linkend="cairo-image-surface-create-from-png">cairo_image_surface_create_from_png</link> (<parameter>const <link linkend="char"><type>char</type></link> *filename</parameter>); <link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link> (<link linkend="cairo-read-func-t">*cairo_read_func_t</link>) (<parameter><link linkend="void"><type>void</type></link> *closure</parameter>, <parameter>unsigned <link linkend="char"><type>char</type></link> *data</parameter>, <parameter>unsigned <link linkend="int"><type>int</type></link> length</parameter>); <link linkend="cairo-surface-t"><returnvalue>cairo_surface_t</returnvalue></link> * <link linkend="cairo-image-surface-create-from-png-stream">cairo_image_surface_create_from_png_stream</link> (<parameter><link linkend="cairo-read-func-t"><type>cairo_read_func_t</type></link> read_func</parameter>, <parameter><link linkend="void"><type>void</type></link> *closure</parameter>); <link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link> <link linkend="cairo-surface-write-to-png">cairo_surface_write_to_png</link> (<parameter><link linkend="cairo-surface-t"><type>cairo_surface_t</type></link> *surface</parameter>, <parameter>const <link linkend="char"><type>char</type></link> *filename</parameter>); <link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link> (<link linkend="cairo-write-func-t">*cairo_write_func_t</link>) (<parameter><link linkend="void"><type>void</type></link> *closure</parameter>, <parameter>unsigned <link linkend="char"><type>char</type></link> *data</parameter>, <parameter>unsigned <link linkend="int"><type>int</type></link> length</parameter>); <link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link> <link linkend="cairo-surface-write-to-png-stream">cairo_surface_write_to_png_stream</link> (<parameter><link linkend="cairo-surface-t"><type>cairo_surface_t</type></link> *surface</parameter>, <parameter><link linkend="cairo-write-func-t"><type>cairo_write_func_t</type></link> write_func</parameter>, <parameter><link linkend="void"><type>void</type></link> *closure</parameter>); </synopsis> </refsynopsisdiv> <refsect1 id="cairo-PNG-Support.description" role="desc"> <title role="desc.title">Description</title> <para> The PNG functions allow reading PNG images into image surfaces, and writing any surface to a PNG file. </para> </refsect1> <refsect1 id="cairo-PNG-Support.details" role="details"> <title role="details.title">Details</title> <refsect2 id="CAIRO-HAS-PNG-FUNCTIONS:CAPS" role="macro"> <title>CAIRO_HAS_PNG_FUNCTIONS</title> <indexterm zone="CAIRO-HAS-PNG-FUNCTIONS:CAPS"><primary sortas="HAS_PNG_FUNCTIONS">CAIRO_HAS_PNG_FUNCTIONS</primary></indexterm> <programlisting>#define CAIRO_HAS_PNG_FUNCTIONS 1 </programlisting> <para> Defined if the PNG functions are available. This macro can be used to conditionally compile code using the cairo PNG functions. </para></refsect2> <refsect2 id="cairo-image-surface-create-from-png" role="function"> <title>cairo_image_surface_create_from_png ()</title> <indexterm zone="cairo-image-surface-create-from-png"><primary sortas="image_surface_create_from_png">cairo_image_surface_create_from_png</primary></indexterm> <programlisting><link linkend="cairo-surface-t"><returnvalue>cairo_surface_t</returnvalue></link> * cairo_image_surface_create_from_png (<parameter>const <link linkend="char"><type>char</type></link> *filename</parameter>);</programlisting> <para> Creates a new image surface and initializes the contents to the given PNG file. </para><variablelist role="params"> <varlistentry><term><parameter>filename</parameter> :</term> <listitem><simpara>name of PNG file to load </simpara></listitem></varlistentry> <varlistentry><term><emphasis>Returns</emphasis> :</term><listitem><simpara> a new <link linkend="cairo-surface-t"><type>cairo_surface_t</type></link> 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: <link linkend="CAIRO-STATUS-NO-MEMORY:CAPS"><literal>CAIRO_STATUS_NO_MEMORY</literal></link> <link linkend="CAIRO-STATUS-FILE-NOT-FOUND:CAPS"><literal>CAIRO_STATUS_FILE_NOT_FOUND</literal></link> <link linkend="CAIRO-STATUS-READ-ERROR:CAPS"><literal>CAIRO_STATUS_READ_ERROR</literal></link> Alternatively, you can allow errors to propagate through the drawing operations and check the status on the context upon completion using <link linkend="cairo-status"><function>cairo_status()</function></link>. </simpara></listitem></varlistentry> </variablelist></refsect2> <refsect2 id="cairo-read-func-t" role="function"> <title>cairo_read_func_t ()</title> <indexterm zone="cairo-read-func-t"><primary sortas="read_func_t">cairo_read_func_t</primary></indexterm> <programlisting><link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link> (*cairo_read_func_t) (<parameter><link linkend="void"><type>void</type></link> *closure</parameter>, <parameter>unsigned <link linkend="char"><type>char</type></link> *data</parameter>, <parameter>unsigned <link linkend="int"><type>int</type></link> length</parameter>);</programlisting> <para> <link linkend="cairo-read-func-t"><type>cairo_read_func_t</type></link> 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 <link linkend="CAIRO-STATUS-SUCCESS:CAPS"><literal>CAIRO_STATUS_SUCCESS</literal></link> if all the data was successfully read, <link linkend="CAIRO-STATUS-READ-ERROR:CAPS"><literal>CAIRO_STATUS_READ_ERROR</literal></link> otherwise. </para><variablelist role="params"> <varlistentry><term><parameter>closure</parameter> :</term> <listitem><simpara>the input closure </simpara></listitem></varlistentry> <varlistentry><term><parameter>data</parameter> :</term> <listitem><simpara>the buffer into which to read the data </simpara></listitem></varlistentry> <varlistentry><term><parameter>length</parameter> :</term> <listitem><simpara>the amount of data to read </simpara></listitem></varlistentry> <varlistentry><term><emphasis>Returns</emphasis> :</term><listitem><simpara> the status code of the read operation </simpara></listitem></varlistentry> </variablelist></refsect2> <refsect2 id="cairo-image-surface-create-from-png-stream" role="function"> <title>cairo_image_surface_create_from_png_stream ()</title> <indexterm zone="cairo-image-surface-create-from-png-stream"><primary sortas="image_surface_create_from_png_stream">cairo_image_surface_create_from_png_stream</primary></indexterm> <programlisting><link linkend="cairo-surface-t"><returnvalue>cairo_surface_t</returnvalue></link> * cairo_image_surface_create_from_png_stream (<parameter><link linkend="cairo-read-func-t"><type>cairo_read_func_t</type></link> read_func</parameter>, <parameter><link linkend="void"><type>void</type></link> *closure</parameter>);</programlisting> <para> Creates a new image surface from PNG data read incrementally via the <parameter>read_func</parameter> function. </para><variablelist role="params"> <varlistentry><term><parameter>read_func</parameter> :</term> <listitem><simpara>function called to read the data of the file </simpara></listitem></varlistentry> <varlistentry><term><parameter>closure</parameter> :</term> <listitem><simpara>data to pass to <parameter>read_func</parameter>. </simpara></listitem></varlistentry> <varlistentry><term><emphasis>Returns</emphasis> :</term><listitem><simpara> a new <link linkend="cairo-surface-t"><type>cairo_surface_t</type></link> 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: <link linkend="CAIRO-STATUS-NO-MEMORY:CAPS"><literal>CAIRO_STATUS_NO_MEMORY</literal></link> <link linkend="CAIRO-STATUS-READ-ERROR:CAPS"><literal>CAIRO_STATUS_READ_ERROR</literal></link> Alternatively, you can allow errors to propagate through the drawing operations and check the status on the context upon completion using <link linkend="cairo-status"><function>cairo_status()</function></link>. </simpara></listitem></varlistentry> </variablelist></refsect2> <refsect2 id="cairo-surface-write-to-png" role="function"> <title>cairo_surface_write_to_png ()</title> <indexterm zone="cairo-surface-write-to-png"><primary sortas="surface_write_to_png">cairo_surface_write_to_png</primary></indexterm> <programlisting><link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link> cairo_surface_write_to_png (<parameter><link linkend="cairo-surface-t"><type>cairo_surface_t</type></link> *surface</parameter>, <parameter>const <link linkend="char"><type>char</type></link> *filename</parameter>);</programlisting> <para> Writes the contents of <parameter>surface</parameter> to a new file <parameter>filename</parameter> as a PNG image. </para><variablelist role="params"> <varlistentry><term><parameter>surface</parameter> :</term> <listitem><simpara>a <link linkend="cairo-surface-t"><type>cairo_surface_t</type></link> with pixel contents </simpara></listitem></varlistentry> <varlistentry><term><parameter>filename</parameter> :</term> <listitem><simpara>the name of a file to write to </simpara></listitem></varlistentry> <varlistentry><term><emphasis>Returns</emphasis> :</term><listitem><simpara> <link linkend="CAIRO-STATUS-SUCCESS:CAPS"><literal>CAIRO_STATUS_SUCCESS</literal></link> if the PNG file was written successfully. Otherwise, <link linkend="CAIRO-STATUS-NO-MEMORY:CAPS"><literal>CAIRO_STATUS_NO_MEMORY</literal></link> if memory could not be allocated for the operation or <link linkend="CAIRO-STATUS-SURFACE-TYPE-MISMATCH:CAPS"><literal>CAIRO_STATUS_SURFACE_TYPE_MISMATCH</literal></link> if the surface does not have pixel contents, or <link linkend="CAIRO-STATUS-WRITE-ERROR:CAPS"><literal>CAIRO_STATUS_WRITE_ERROR</literal></link> if an I/O error occurs while attempting to write the file. </simpara></listitem></varlistentry> </variablelist></refsect2> <refsect2 id="cairo-write-func-t" role="function"> <title>cairo_write_func_t ()</title> <indexterm zone="cairo-write-func-t"><primary sortas="write_func_t">cairo_write_func_t</primary></indexterm> <programlisting><link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link> (*cairo_write_func_t) (<parameter><link linkend="void"><type>void</type></link> *closure</parameter>, <parameter>unsigned <link linkend="char"><type>char</type></link> *data</parameter>, <parameter>unsigned <link linkend="int"><type>int</type></link> length</parameter>);</programlisting> <para> <link linkend="cairo-write-func-t"><type>cairo_write_func_t</type></link> 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 <link linkend="CAIRO-STATUS-SUCCESS:CAPS"><literal>CAIRO_STATUS_SUCCESS</literal></link> if all the data was successfully written, <link linkend="CAIRO-STATUS-WRITE-ERROR:CAPS"><literal>CAIRO_STATUS_WRITE_ERROR</literal></link> otherwise. </para><variablelist role="params"> <varlistentry><term><parameter>closure</parameter> :</term> <listitem><simpara>the output closure </simpara></listitem></varlistentry> <varlistentry><term><parameter>data</parameter> :</term> <listitem><simpara>the buffer containing the data to write </simpara></listitem></varlistentry> <varlistentry><term><parameter>length</parameter> :</term> <listitem><simpara>the amount of data to write </simpara></listitem></varlistentry> <varlistentry><term><emphasis>Returns</emphasis> :</term><listitem><simpara> the status code of the write operation </simpara></listitem></varlistentry> </variablelist></refsect2> <refsect2 id="cairo-surface-write-to-png-stream" role="function"> <title>cairo_surface_write_to_png_stream ()</title> <indexterm zone="cairo-surface-write-to-png-stream"><primary sortas="surface_write_to_png_stream">cairo_surface_write_to_png_stream</primary></indexterm> <programlisting><link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link> cairo_surface_write_to_png_stream (<parameter><link linkend="cairo-surface-t"><type>cairo_surface_t</type></link> *surface</parameter>, <parameter><link linkend="cairo-write-func-t"><type>cairo_write_func_t</type></link> write_func</parameter>, <parameter><link linkend="void"><type>void</type></link> *closure</parameter>);</programlisting> <para> Writes the image surface to the write function. </para><variablelist role="params"> <varlistentry><term><parameter>surface</parameter> :</term> <listitem><simpara>a <link linkend="cairo-surface-t"><type>cairo_surface_t</type></link> with pixel contents </simpara></listitem></varlistentry> <varlistentry><term><parameter>write_func</parameter> :</term> <listitem><simpara>a <link linkend="cairo-write-func-t"><type>cairo_write_func_t</type></link> </simpara></listitem></varlistentry> <varlistentry><term><parameter>closure</parameter> :</term> <listitem><simpara>closure data for the write function </simpara></listitem></varlistentry> <varlistentry><term><emphasis>Returns</emphasis> :</term><listitem><simpara> <link linkend="CAIRO-STATUS-SUCCESS:CAPS"><literal>CAIRO_STATUS_SUCCESS</literal></link> if the PNG file was written successfully. Otherwise, <link linkend="CAIRO-STATUS-NO-MEMORY:CAPS"><literal>CAIRO_STATUS_NO_MEMORY</literal></link> is returned if memory could not be allocated for the operation, <link linkend="CAIRO-STATUS-SURFACE-TYPE-MISMATCH:CAPS"><literal>CAIRO_STATUS_SURFACE_TYPE_MISMATCH</literal></link> if the surface does not have pixel contents. </simpara></listitem></varlistentry> </variablelist></refsect2> </refsect1> <refsect1 id="cairo-PNG-Support.see-also"> <title>See Also</title> <link linkend="cairo-surface-t"><type>cairo_surface_t</type></link> </refsect1> </refentry>