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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.imagecolorallocatealpha" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>imagecolorallocatealpha</refname>
<refpurpose>Allocate a color for an image</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type class="union"><type>int</type><type>false</type></type><methodname>imagecolorallocatealpha</methodname>
<methodparam><type>GdImage</type><parameter>image</parameter></methodparam>
<methodparam><type>int</type><parameter>red</parameter></methodparam>
<methodparam><type>int</type><parameter>green</parameter></methodparam>
<methodparam><type>int</type><parameter>blue</parameter></methodparam>
<methodparam><type>int</type><parameter>alpha</parameter></methodparam>
</methodsynopsis>
<para>
<function>imagecolorallocatealpha</function> behaves identically to
<function>imagecolorallocate</function> with the addition of the transparency
parameter <parameter>alpha</parameter>.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
&gd.image.description;
<varlistentry>
<term><parameter>red</parameter></term>
<listitem>
<para>&gd.value.red;</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>green</parameter></term>
<listitem>
<para>&gd.value.green;</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>blue</parameter></term>
<listitem>
<para>&gd.value.blue;</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>alpha</parameter></term>
<listitem>
<para>
A value between <literal>0</literal> and <literal>127</literal>.
<literal>0</literal> indicates completely opaque while
<literal>127</literal> indicates completely transparent.
</para>
</listitem>
</varlistentry>
</variablelist>
The <parameter>red</parameter>, <parameter>green</parameter>
and <parameter>blue</parameter> parameters are integers
between 0 and 255 or hexadecimals between 0x00 and 0xFF.
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
A color identifier or &false; if the allocation failed.
</para>
&return.falseproblem;
</refsect1>
<refsect1 role="changelog">
&reftitle.changelog;
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>&Version;</entry>
<entry>&Description;</entry>
</row>
</thead>
<tbody>
&gd.changelog.image-param;
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<example>
<title>Example of using <function>imagecolorallocatealpha</function></title>
<programlisting role="php">
<![CDATA[
<?php
$size = 300;
$image=imagecreatetruecolor($size, $size);
// something to get a white background with black border
$back = imagecolorallocate($image, 255, 255, 255);
$border = imagecolorallocate($image, 0, 0, 0);
imagefilledrectangle($image, 0, 0, $size - 1, $size - 1, $back);
imagerectangle($image, 0, 0, $size - 1, $size - 1, $border);
$yellow_x = 100;
$yellow_y = 75;
$red_x = 120;
$red_y = 165;
$blue_x = 187;
$blue_y = 125;
$radius = 150;
// allocate colors with alpha values
$yellow = imagecolorallocatealpha($image, 255, 255, 0, 75);
$red = imagecolorallocatealpha($image, 255, 0, 0, 75);
$blue = imagecolorallocatealpha($image, 0, 0, 255, 75);
// drawing 3 overlapped circle
imagefilledellipse($image, $yellow_x, $yellow_y, $radius, $radius, $yellow);
imagefilledellipse($image, $red_x, $red_y, $radius, $radius, $red);
imagefilledellipse($image, $blue_x, $blue_y, $radius, $radius, $blue);
// don't forget to output a correct header!
header('Content-Type: image/png');
// and finally, output the result
imagepng($image);
imagedestroy($image);
?>
]]>
</programlisting>
&example.outputs.similar;
<mediaobject>
<alt>Output of example : Example of using imagecolorallocatealpha()</alt>
<imageobject>
<imagedata fileref="en/reference/image/figures/imagecolorallocatealpha.png"/>
</imageobject>
</mediaobject>
</example>
<example xml:id="imagecolorallocatealpha.example.convert">
<title>Convert typical alpha values for use with <function>imagecolorallocatealpha</function></title>
<para>
Usually alpha values of <literal>0</literal> designate fully transparent pixels,
and the alpha channel has 8 bits. To convert such alpha values to be compatible
with <function>imagecolorallocatealpha</function>, some simple arithmetic is
sufficient:
</para>
<programlisting role="php">
<![CDATA[
<?php
$alpha8 = 0; // fully transparent
var_dump(127 - ($alpha8 >> 1));
$alpha8 = 255; // fully opaque
var_dump(127 - ($alpha8 >> 1));
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
int(127)
int(0)
]]>
</screen>
</example>
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<simplelist>
<member><function>imagecolorallocate</function></member>
<member><function>imagecolordeallocate</function></member>
</simplelist>
</refsect1>
</refentry>
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-->
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