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+<refentry id="vidioc-g-selection">
+
+ <refmeta>
+ <refentrytitle>ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION</refentrytitle>
+ &manvol;
+ </refmeta>
+
+ <refnamediv>
+ <refname>VIDIOC_G_SELECTION</refname>
+ <refname>VIDIOC_S_SELECTION</refname>
+ <refpurpose>Get or set one of the selection rectangles</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcprototype>
+ <funcdef>int <function>ioctl</function></funcdef>
+ <paramdef>int <parameter>fd</parameter></paramdef>
+ <paramdef>int <parameter>request</parameter></paramdef>
+ <paramdef>struct v4l2_selection *<parameter>argp</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Arguments</title>
+
+ <variablelist>
+ <varlistentry>
+ <term><parameter>fd</parameter></term>
+ <listitem>
+ <para>&fd;</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>request</parameter></term>
+ <listitem>
+ <para>VIDIOC_G_SELECTION, VIDIOC_S_SELECTION</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>argp</parameter></term>
+ <listitem>
+ <para></para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+ <refsect1>
+ <title>Description</title>
+
+ <note>
+ <title>Experimental</title>
+ <para>This is an <link linkend="experimental"> experimental </link>
+ interface and may change in the future.</para>
+ </note>
+
+ <para>The ioctls are used to query and configure selection rectangles.</para>
+
+<para> To query the cropping (composing) rectangle set <structfield>
+&v4l2-selection;::type </structfield> to the respective buffer type. Do not
+use multiplanar buffers. Use <constant> V4L2_BUF_TYPE_VIDEO_CAPTURE
+</constant> instead of <constant> V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE
+</constant>. Use <constant> V4L2_BUF_TYPE_VIDEO_OUTPUT </constant> instead of
+<constant> V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE </constant>. The next step is
+setting <structfield> &v4l2-selection;::target </structfield> to value
+<constant> V4L2_SEL_TGT_CROP_ACTIVE </constant> (<constant>
+V4L2_SEL_TGT_COMPOSE_ACTIVE </constant>). Please refer to table <xref
+linkend="v4l2-sel-target" /> or <xref linkend="selection-api" /> for additional
+targets. Fields <structfield> &v4l2-selection;::flags </structfield> and
+<structfield> &v4l2-selection;::reserved </structfield> are ignored and they
+must be filled with zeros. The driver fills the rest of the structure or
+returns &EINVAL; if incorrect buffer type or target was used. If cropping
+(composing) is not supported then the active rectangle is not mutable and it is
+always equal to the bounds rectangle. Finally, structure <structfield>
+&v4l2-selection;::r </structfield> is filled with the current cropping
+(composing) coordinates. The coordinates are expressed in driver-dependent
+units. The only exception are rectangles for images in raw formats, whose
+coordinates are always expressed in pixels. </para>
+
+<para> To change the cropping (composing) rectangle set <structfield>
+&v4l2-selection;::type </structfield> to the respective buffer type. Do not
+use multiplanar buffers. Use <constant> V4L2_BUF_TYPE_VIDEO_CAPTURE
+</constant> instead of <constant> V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE
+</constant>. Use <constant> V4L2_BUF_TYPE_VIDEO_OUTPUT </constant> instead of
+<constant> V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE </constant>. The next step is
+setting <structfield> &v4l2-selection;::target </structfield> to value
+<constant> V4L2_SEL_TGT_CROP_ACTIVE </constant> (<constant>
+V4L2_SEL_TGT_COMPOSE_ACTIVE </constant>). Please refer to table <xref
+linkend="v4l2-sel-target" /> or <xref linkend="selection-api" /> for additional
+targets. Set desired active area into the field <structfield>
+&v4l2-selection;::r </structfield>. Field <structfield>
+&v4l2-selection;::reserved </structfield> is ignored and must be filled with
+zeros. The driver may adjust the rectangle coordinates. An application may
+introduce constraints to control rounding behaviour. Set the field
+<structfield> &v4l2-selection;::flags </structfield> to one of values:
+
+<itemizedlist>
+ <listitem>
+<para><constant>0</constant> - The driver can adjust the rectangle size freely
+and shall choose a crop/compose rectangle as close as possible to the requested
+one.</para>
+ </listitem>
+ <listitem>
+<para><constant>V4L2_SEL_FLAG_GE</constant> - The driver is not allowed to
+shrink the rectangle. The original rectangle must lay inside the adjusted
+one.</para>
+ </listitem>
+ <listitem>
+<para><constant>V4L2_SEL_FLAG_LE</constant> - The driver is not allowed to
+enlarge the rectangle. The adjusted rectangle must lay inside the original
+one.</para>
+ </listitem>
+ <listitem>
+<para><constant>V4L2_SEL_FLAG_GE | V4L2_SEL_FLAG_LE</constant> - The driver
+must choose the size exactly the same as in the requested rectangle.</para>
+ </listitem>
+</itemizedlist>
+
+Please refer to <xref linkend="sel-const-adjust" />.
+
+</para>
+
+<para> The driver may have to adjusts the requested dimensions against hardware
+limits and other parts as the pipeline, i.e. the bounds given by the
+capture/output window or TV display. The closest possible values of horizontal
+and vertical offset and sizes are chosen according to following priority:
+
+<orderedlist>
+ <listitem>
+ <para>Satisfy constraints from <structfield>&v4l2-selection;::flags</structfield>.</para>
+ </listitem>
+ <listitem>
+ <para>Adjust width, height, left, and top to hardware limits and alignments.</para>
+ </listitem>
+ <listitem>
+ <para>Keep center of adjusted rectangle as close as possible to the original one.</para>
+ </listitem>
+ <listitem>
+ <para>Keep width and height as close as possible to original ones.</para>
+ </listitem>
+ <listitem>
+ <para>Keep horizontal and vertical offset as close as possible to original ones.</para>
+ </listitem>
+</orderedlist>
+
+On success the field <structfield> &v4l2-selection;::r </structfield> contains
+the adjusted rectangle. When the parameters are unsuitable the application may
+modify the cropping (composing) or image parameters and repeat the cycle until
+satisfactory parameters have been negotiated. If constraints flags have to be
+violated at then ERANGE is returned. The error indicates that <emphasis> there
+exist no rectangle </emphasis> that satisfies the constraints.</para>
+
+ </refsect1>
+
+ <refsect1>
+ <table frame="none" pgwide="1" id="v4l2-sel-target">
+ <title>Selection targets.</title>
+ <tgroup cols="3">
+ &cs-def;
+ <tbody valign="top">
+ <row>
+ <entry><constant>V4L2_SEL_TGT_CROP_ACTIVE</constant></entry>
+ <entry>0</entry>
+ <entry>area that is currently cropped by hardware</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_SEL_TGT_CROP_DEFAULT</constant></entry>
+ <entry>1</entry>
+ <entry>suggested cropping rectangle that covers the "whole picture"</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_SEL_TGT_CROP_BOUNDS</constant></entry>
+ <entry>2</entry>
+ <entry>limits for the cropping rectangle</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_SEL_TGT_COMPOSE_ACTIVE</constant></entry>
+ <entry>256</entry>
+ <entry>area to which data are composed by hardware</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_SEL_TGT_COMPOSE_DEFAULT</constant></entry>
+ <entry>257</entry>
+ <entry>suggested composing rectangle that covers the "whole picture"</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_SEL_TGT_COMPOSE_BOUNDS</constant></entry>
+ <entry>258</entry>
+ <entry>limits for the composing rectangle</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_SEL_TGT_COMPOSE_PADDED</constant></entry>
+ <entry>259</entry>
+ <entry>the active area and all padding pixels that are inserted or modified by the hardware</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ </refsect1>
+
+ <refsect1>
+ <table frame="none" pgwide="1" id="v4l2-sel-flags">
+ <title>Selection constraint flags</title>
+ <tgroup cols="3">
+ &cs-def;
+ <tbody valign="top">
+ <row>
+ <entry><constant>V4L2_SEL_FLAG_GE</constant></entry>
+ <entry>0x00000001</entry>
+ <entry>indicate that adjusted rectangle must contain a rectangle from <structfield>&v4l2-selection;::r</structfield></entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_SEL_FLAG_LE</constant></entry>
+ <entry>0x00000002</entry>
+ <entry>indicate that adjusted rectangle must be inside a rectangle from <structfield>&v4l2-selection;::r</structfield></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ </refsect1>
+
+ <section>
+ <figure id="sel-const-adjust">
+ <title>Size adjustments with constraint flags.</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="constraints.png" format="PNG" />
+ </imageobject>
+ <textobject>
+ <phrase>Behaviour of rectangle adjustment for different constraint
+ flags.</phrase>
+ </textobject>
+ </mediaobject>
+ </figure>
+ </section>
+
+ <refsect1>
+ <table pgwide="1" frame="none" id="v4l2-selection">
+ <title>struct <structname>v4l2_selection</structname></title>
+ <tgroup cols="3">
+ &cs-str;
+ <tbody valign="top">
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>type</structfield></entry>
+ <entry>Type of the buffer (from &v4l2-buf-type;)</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>target</structfield></entry>
+ <entry>used to select between <link linkend="v4l2-sel-target"> cropping and composing rectangles </link></entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>flags</structfield></entry>
+ <entry>control over coordinates adjustments, refer to <link linkend="v4l2-sel-flags">selection flags</link></entry>
+ </row>
+ <row>
+ <entry>&v4l2-rect;</entry>
+ <entry><structfield>r</structfield></entry>
+ <entry>selection rectangle</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>reserved[9]</structfield></entry>
+ <entry>Reserved fields for future use</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ </refsect1>
+
+ <refsect1>
+ &return-value;
+ <variablelist>
+ <varlistentry>
+ <term><errorcode>EINVAL</errorcode></term>
+ <listitem>
+ <para>The buffer <structfield> &v4l2-selection;::type </structfield>
+or <structfield> &v4l2-selection;::target </structfield> is not supported, or
+the <structfield> &v4l2-selection;::flags </structfield> are invalid.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><errorcode>ERANGE</errorcode></term>
+ <listitem>
+ <para>it is not possible to adjust a rectangle <structfield>
+&v4l2-selection;::r </structfield> that satisfies all contraints from
+<structfield> &v4l2-selection;::flags </structfield>.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><errorcode>EBUSY</errorcode></term>
+ <listitem>
+ <para>it is not possible to apply change of selection rectangle at the moment.
+Usually because streaming is in progress.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+</refentry>