path: root/libs/cairo-1.16.0/doc/public/xml/cairo-png.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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<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>

<refsect1 id="cairo-PNG-Support.functions" role="functions_proto">
<title role="functions_proto.title">Functions</title>
<informaltable pgwide="1" frame="none">
<tgroup cols="2">
<colspec colname="functions_return" colwidth="150px"/>
<colspec colname="functions_name"/>
<tbody>
<row><entry role="function_type"><link linkend="cairo-surface-t"><returnvalue>cairo_surface_t</returnvalue></link>&#160;*
</entry><entry role="function_name"><link linkend="cairo-image-surface-create-from-png">cairo_image_surface_create_from_png</link>&#160;<phrase role="c_punctuation">()</phrase></entry></row>
<row><entry role="function_type"><link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link>
</entry><entry role="function_name"><phrase role="c_punctuation">(</phrase><link linkend="cairo-read-func-t">*cairo_read_func_t</link><phrase role="c_punctuation">)</phrase>&#160;<phrase role="c_punctuation">()</phrase></entry></row>
<row><entry role="function_type"><link linkend="cairo-surface-t"><returnvalue>cairo_surface_t</returnvalue></link>&#160;*
</entry><entry role="function_name"><link linkend="cairo-image-surface-create-from-png-stream">cairo_image_surface_create_from_png_stream</link>&#160;<phrase role="c_punctuation">()</phrase></entry></row>
<row><entry role="function_type"><link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link>
</entry><entry role="function_name"><link linkend="cairo-surface-write-to-png">cairo_surface_write_to_png</link>&#160;<phrase role="c_punctuation">()</phrase></entry></row>
<row><entry role="function_type"><link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link>
</entry><entry role="function_name"><phrase role="c_punctuation">(</phrase><link linkend="cairo-write-func-t">*cairo_write_func_t</link><phrase role="c_punctuation">)</phrase>&#160;<phrase role="c_punctuation">()</phrase></entry></row>
<row><entry role="function_type"><link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link>
</entry><entry role="function_name"><link linkend="cairo-surface-write-to-png-stream">cairo_surface_write_to_png_stream</link>&#160;<phrase role="c_punctuation">()</phrase></entry></row>

</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 id="cairo-PNG-Support.other" role="other_proto">
<title role="other_proto.title">Types and Values</title>
<informaltable role="enum_members_table" pgwide="1" frame="none">
<tgroup cols="2">
<colspec colname="name" colwidth="150px"/>
<colspec colname="description"/>
<tbody>
<row><entry role="define_keyword">#define</entry><entry role="function_name"><link linkend="CAIRO-HAS-PNG-FUNCTIONS:CAPS">CAIRO_HAS_PNG_FUNCTIONS</link></entry></row>

</tbody>
</tgroup>
</informaltable>
</refsect1>


<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>
<para>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
<link linkend="cairo-image-surface-get-data"><function>cairo_image_surface_get_data()</function></link> or a backend-specific access
function, and process it with another library, e.g. gdk-pixbuf or
libpng.</para>

</refsect1>
<refsect1 id="cairo-PNG-Support.functions_details" role="details">
<title role="details.title">Functions</title>
<refsect2 id="cairo-image-surface-create-from-png" role="function" condition="since:1.0">
<title>cairo_image_surface_create_from_png&#160;()</title>
<indexterm zone="cairo-image-surface-create-from-png" role="1.0"><primary sortas="image_surface_create_from_png">cairo_image_surface_create_from_png</primary></indexterm>
<programlisting language="C"><link linkend="cairo-surface-t"><returnvalue>cairo_surface_t</returnvalue></link>&#160;*
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>
<refsect3 id="cairo-image-surface-create-from-png.parameters" role="parameters">
<title>Parameters</title>
<informaltable role="parameters_table" pgwide="1" frame="none">
<tgroup cols="3">
<colspec colname="parameters_name" colwidth="150px"/>
<colspec colname="parameters_description"/>
<colspec colname="parameters_annotations" colwidth="200px"/>
<tbody>
<row><entry role="parameter_name"><para>filename</para></entry>
<entry role="parameter_description"><para>name of PNG file to load. On Windows this filename
is encoded in UTF-8.</para></entry>
<entry role="parameter_annotations"></entry></row>
</tbody></tgroup></informaltable>
</refsect3><refsect3 id="cairo-image-surface-create-from-png.returns" role="returns">
<title>Returns</title>
<para> 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:</para>
<para><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>
<link linkend="CAIRO-STATUS-PNG-ERROR:CAPS"><literal>CAIRO_STATUS_PNG_ERROR</literal></link></para>
<para>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>.</para>
</refsect3><para role="since">Since: <link linkend="api-index-1.0">1.0</link></para></refsect2>
<refsect2 id="cairo-read-func-t" role="function" condition="since:1.0">
<title>cairo_read_func_t&#160;()</title>
<indexterm zone="cairo-read-func-t" role="1.0"><primary sortas="read_func_t">cairo_read_func_t</primary></indexterm>
<programlisting language="C"><link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link>
<phrase role="c_punctuation">(</phrase>*cairo_read_func_t<phrase role="c_punctuation">)</phrase> (<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>
<refsect3 id="cairo-read-func-t.parameters" role="parameters">
<title>Parameters</title>
<informaltable role="parameters_table" pgwide="1" frame="none">
<tgroup cols="3">
<colspec colname="parameters_name" colwidth="150px"/>
<colspec colname="parameters_description"/>
<colspec colname="parameters_annotations" colwidth="200px"/>
<tbody>
<row><entry role="parameter_name"><para>closure</para></entry>
<entry role="parameter_description"><para>the input closure</para></entry>
<entry role="parameter_annotations"></entry></row>
<row><entry role="parameter_name"><para>data</para></entry>
<entry role="parameter_description"><para>the buffer into which to read the data</para></entry>
<entry role="parameter_annotations"></entry></row>
<row><entry role="parameter_name"><para>length</para></entry>
<entry role="parameter_description"><para>the amount of data to read</para></entry>
<entry role="parameter_annotations"></entry></row>
</tbody></tgroup></informaltable>
</refsect3><refsect3 id="cairo-read-func-t.returns" role="returns">
<title>Returns</title>
<para> the status code of the read operation</para>
</refsect3><para role="since">Since: <link linkend="api-index-1.0">1.0</link></para></refsect2>
<refsect2 id="cairo-image-surface-create-from-png-stream" role="function" condition="since:1.0">
<title>cairo_image_surface_create_from_png_stream&#160;()</title>
<indexterm zone="cairo-image-surface-create-from-png-stream" role="1.0"><primary sortas="image_surface_create_from_png_stream">cairo_image_surface_create_from_png_stream</primary></indexterm>
<programlisting language="C"><link linkend="cairo-surface-t"><returnvalue>cairo_surface_t</returnvalue></link>&#160;*
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>
<refsect3 id="cairo-image-surface-create-from-png-stream.parameters" role="parameters">
<title>Parameters</title>
<informaltable role="parameters_table" pgwide="1" frame="none">
<tgroup cols="3">
<colspec colname="parameters_name" colwidth="150px"/>
<colspec colname="parameters_description"/>
<colspec colname="parameters_annotations" colwidth="200px"/>
<tbody>
<row><entry role="parameter_name"><para>read_func</para></entry>
<entry role="parameter_description"><para>function called to read the data of the file</para></entry>
<entry role="parameter_annotations"></entry></row>
<row><entry role="parameter_name"><para>closure</para></entry>
<entry role="parameter_description"><para>data to pass to <parameter>read_func</parameter>
.</para></entry>
<entry role="parameter_annotations"></entry></row>
</tbody></tgroup></informaltable>
</refsect3><refsect3 id="cairo-image-surface-create-from-png-stream.returns" role="returns">
<title>Returns</title>
<para> 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:</para>
<para><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>
<link linkend="CAIRO-STATUS-PNG-ERROR:CAPS"><literal>CAIRO_STATUS_PNG_ERROR</literal></link></para>
<para>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>.</para>
</refsect3><para role="since">Since: <link linkend="api-index-1.0">1.0</link></para></refsect2>
<refsect2 id="cairo-surface-write-to-png" role="function" condition="since:1.0">
<title>cairo_surface_write_to_png&#160;()</title>
<indexterm zone="cairo-surface-write-to-png" role="1.0"><primary sortas="surface_write_to_png">cairo_surface_write_to_png</primary></indexterm>
<programlisting language="C"><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>
<refsect3 id="cairo-surface-write-to-png.parameters" role="parameters">
<title>Parameters</title>
<informaltable role="parameters_table" pgwide="1" frame="none">
<tgroup cols="3">
<colspec colname="parameters_name" colwidth="150px"/>
<colspec colname="parameters_description"/>
<colspec colname="parameters_annotations" colwidth="200px"/>
<tbody>
<row><entry role="parameter_name"><para>surface</para></entry>
<entry role="parameter_description"><para>a <link linkend="cairo-surface-t"><type>cairo_surface_t</type></link> with pixel contents</para></entry>
<entry role="parameter_annotations"></entry></row>
<row><entry role="parameter_name"><para>filename</para></entry>
<entry role="parameter_description"><para>the name of a file to write to; on Windows this filename
is encoded in UTF-8.</para></entry>
<entry role="parameter_annotations"></entry></row>
</tbody></tgroup></informaltable>
</refsect3><refsect3 id="cairo-surface-write-to-png.returns" role="returns">
<title>Returns</title>
<para> <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, or <link linkend="CAIRO-STATUS-PNG-ERROR:CAPS"><literal>CAIRO_STATUS_PNG_ERROR</literal></link> if libpng
returned an error.</para>
</refsect3><para role="since">Since: <link linkend="api-index-1.0">1.0</link></para></refsect2>
<refsect2 id="cairo-write-func-t" role="function" condition="since:1.0">
<title>cairo_write_func_t&#160;()</title>
<indexterm zone="cairo-write-func-t" role="1.0"><primary sortas="write_func_t">cairo_write_func_t</primary></indexterm>
<programlisting language="C"><link linkend="cairo-status-t"><returnvalue>cairo_status_t</returnvalue></link>
<phrase role="c_punctuation">(</phrase>*cairo_write_func_t<phrase role="c_punctuation">)</phrase> (<parameter><link linkend="void"><type>void</type></link> *closure</parameter>,
                       <parameter>const 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>
<refsect3 id="cairo-write-func-t.parameters" role="parameters">
<title>Parameters</title>
<informaltable role="parameters_table" pgwide="1" frame="none">
<tgroup cols="3">
<colspec colname="parameters_name" colwidth="150px"/>
<colspec colname="parameters_description"/>
<colspec colname="parameters_annotations" colwidth="200px"/>
<tbody>
<row><entry role="parameter_name"><para>closure</para></entry>
<entry role="parameter_description"><para>the output closure</para></entry>
<entry role="parameter_annotations"></entry></row>
<row><entry role="parameter_name"><para>data</para></entry>
<entry role="parameter_description"><para>the buffer containing the data to write</para></entry>
<entry role="parameter_annotations"></entry></row>
<row><entry role="parameter_name"><para>length</para></entry>
<entry role="parameter_description"><para>the amount of data to write</para></entry>
<entry role="parameter_annotations"></entry></row>
</tbody></tgroup></informaltable>
</refsect3><refsect3 id="cairo-write-func-t.returns" role="returns">
<title>Returns</title>
<para> the status code of the write operation</para>
</refsect3><para role="since">Since: <link linkend="api-index-1.0">1.0</link></para></refsect2>
<refsect2 id="cairo-surface-write-to-png-stream" role="function" condition="since:1.0">
<title>cairo_surface_write_to_png_stream&#160;()</title>
<indexterm zone="cairo-surface-write-to-png-stream" role="1.0"><primary sortas="surface_write_to_png_stream">cairo_surface_write_to_png_stream</primary></indexterm>
<programlisting language="C"><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>
<refsect3 id="cairo-surface-write-to-png-stream.parameters" role="parameters">
<title>Parameters</title>
<informaltable role="parameters_table" pgwide="1" frame="none">
<tgroup cols="3">
<colspec colname="parameters_name" colwidth="150px"/>
<colspec colname="parameters_description"/>
<colspec colname="parameters_annotations" colwidth="200px"/>
<tbody>
<row><entry role="parameter_name"><para>surface</para></entry>
<entry role="parameter_description"><para>a <link linkend="cairo-surface-t"><type>cairo_surface_t</type></link> with pixel contents</para></entry>
<entry role="parameter_annotations"></entry></row>
<row><entry role="parameter_name"><para>write_func</para></entry>
<entry role="parameter_description"><para>a <link linkend="cairo-write-func-t"><type>cairo_write_func_t</type></link></para></entry>
<entry role="parameter_annotations"></entry></row>
<row><entry role="parameter_name"><para>closure</para></entry>
<entry role="parameter_description"><para>closure data for the write function</para></entry>
<entry role="parameter_annotations"></entry></row>
</tbody></tgroup></informaltable>
</refsect3><refsect3 id="cairo-surface-write-to-png-stream.returns" role="returns">
<title>Returns</title>
<para> <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, or <link linkend="CAIRO-STATUS-PNG-ERROR:CAPS"><literal>CAIRO_STATUS_PNG_ERROR</literal></link> if libpng
returned an error.</para>
</refsect3><para role="since">Since: <link linkend="api-index-1.0">1.0</link></para></refsect2>

</refsect1>
<refsect1 id="cairo-PNG-Support.other_details" role="details">
<title role="details.title">Types and Values</title>
<refsect2 id="CAIRO-HAS-PNG-FUNCTIONS:CAPS" role="macro" condition="since:1.0">
<title>CAIRO_HAS_PNG_FUNCTIONS</title>
<indexterm zone="CAIRO-HAS-PNG-FUNCTIONS:CAPS" role="1.0"><primary sortas="HAS_PNG_FUNCTIONS">CAIRO_HAS_PNG_FUNCTIONS</primary></indexterm>
<programlisting language="C">#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>
<para role="since">Since: <link linkend="api-index-1.0">1.0</link></para></refsect2>

</refsect1>
<refsect1 id="cairo-PNG-Support.see-also">
<title>See Also</title>
<para><link linkend="cairo-surface-t"><type>cairo_surface_t</type></link></para>

</refsect1>

</refentry>