234 lines
8.6 KiB
XML
234 lines
8.6 KiB
XML
<refentry id="vidioc-g-selection">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_G_SELECTION</refname>
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<refname>VIDIOC_S_SELECTION</refname>
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<refpurpose>Get or set one of the selection rectangles</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_selection *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_G_SELECTION, VIDIOC_S_SELECTION</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>The ioctls are used to query and configure selection rectangles.</para>
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<para>To query the cropping (composing) rectangle set &v4l2-selection;
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<structfield> type </structfield> field to the respective buffer type.
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Do not use the multiplanar buffer types. Use <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>
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instead of <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant> and use
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<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant> instead of
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<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE</constant>. The next step is
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setting the value of &v4l2-selection; <structfield>target</structfield> field
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to <constant>V4L2_SEL_TGT_CROP</constant> (<constant>V4L2_SEL_TGT_COMPOSE</constant>).
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Please refer to table <xref linkend="v4l2-selections-common" /> or <xref linkend="selection-api" />
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for additional targets. The <structfield>flags</structfield> and <structfield>reserved
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</structfield> fields of &v4l2-selection; are ignored and they must be filled
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with zeros. The driver fills the rest of the structure or
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returns &EINVAL; if incorrect buffer type or target was used. If cropping
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(composing) is not supported then the active rectangle is not mutable and it is
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always equal to the bounds rectangle. Finally, the &v4l2-rect;
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<structfield>r</structfield> rectangle is filled with the current cropping
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(composing) coordinates. The coordinates are expressed in driver-dependent
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units. The only exception are rectangles for images in raw formats, whose
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coordinates are always expressed in pixels.</para>
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<para>To change the cropping (composing) rectangle set the &v4l2-selection;
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<structfield>type</structfield> field to the respective buffer type. Do not
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use multiplanar buffers. Use <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>
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instead of <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant>. Use
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<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant> instead of
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<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE</constant>. The next step is
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setting the value of &v4l2-selection; <structfield>target</structfield> to
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<constant>V4L2_SEL_TGT_CROP</constant> (<constant>V4L2_SEL_TGT_COMPOSE</constant>).
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Please refer to table <xref linkend="v4l2-selections-common" /> or <xref linkend="selection-api" />
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for additional targets. The &v4l2-rect; <structfield>r</structfield> rectangle need to be
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set to the desired active area. Field &v4l2-selection; <structfield> reserved
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</structfield> is ignored and must be filled with zeros. The driver may adjust
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coordinates of the requested rectangle. An application may
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introduce constraints to control rounding behaviour. The &v4l2-selection;
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<structfield>flags</structfield> field must be set to one of the following:
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<itemizedlist>
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<listitem>
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<para><constant>0</constant> - The driver can adjust the rectangle size freely
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and shall choose a crop/compose rectangle as close as possible to the requested
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one.</para>
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</listitem>
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<listitem>
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<para><constant>V4L2_SEL_FLAG_GE</constant> - The driver is not allowed to
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shrink the rectangle. The original rectangle must lay inside the adjusted
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one.</para>
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</listitem>
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<listitem>
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<para><constant>V4L2_SEL_FLAG_LE</constant> - The driver is not allowed to
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enlarge the rectangle. The adjusted rectangle must lay inside the original
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one.</para>
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</listitem>
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<listitem>
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<para><constant>V4L2_SEL_FLAG_GE | V4L2_SEL_FLAG_LE</constant> - The driver
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must choose the size exactly the same as in the requested rectangle.</para>
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</listitem>
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</itemizedlist>
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Please refer to <xref linkend="sel-const-adjust" />.
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</para>
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<para> The driver may have to adjusts the requested dimensions against hardware
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limits and other parts as the pipeline, i.e. the bounds given by the
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capture/output window or TV display. The closest possible values of horizontal
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and vertical offset and sizes are chosen according to following priority:
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<orderedlist>
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<listitem>
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<para>Satisfy constraints from &v4l2-selection; <structfield>flags</structfield>.</para>
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</listitem>
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<listitem>
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<para>Adjust width, height, left, and top to hardware limits and alignments.</para>
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</listitem>
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<listitem>
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<para>Keep center of adjusted rectangle as close as possible to the original one.</para>
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</listitem>
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<listitem>
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<para>Keep width and height as close as possible to original ones.</para>
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</listitem>
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<listitem>
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<para>Keep horizontal and vertical offset as close as possible to original ones.</para>
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</listitem>
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</orderedlist>
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On success the &v4l2-rect; <structfield>r</structfield> field contains
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the adjusted rectangle. When the parameters are unsuitable the application may
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modify the cropping (composing) or image parameters and repeat the cycle until
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satisfactory parameters have been negotiated. If constraints flags have to be
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violated at then ERANGE is returned. The error indicates that <emphasis>there
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exist no rectangle</emphasis> that satisfies the constraints.</para>
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<para>Selection targets and flags are documented in <xref
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linkend="v4l2-selections-common"/>.</para>
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<para>
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<figure id="sel-const-adjust">
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<title>Size adjustments with constraint flags.</title>
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<mediaobject>
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<imageobject>
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<imagedata fileref="constraints.png" format="PNG" />
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</imageobject>
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<textobject>
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<phrase>Behaviour of rectangle adjustment for different constraint
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flags.</phrase>
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</textobject>
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</mediaobject>
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</figure>
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</para>
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<para>
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<table pgwide="1" frame="none" id="v4l2-selection">
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<title>struct <structname>v4l2_selection</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>type</structfield></entry>
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<entry>Type of the buffer (from &v4l2-buf-type;).</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>target</structfield></entry>
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<entry>Used to select between <link linkend="v4l2-selections-common"> cropping
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and composing rectangles</link>.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>flags</structfield></entry>
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<entry>Flags controlling the selection rectangle adjustments, refer to
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<link linkend="v4l2-selection-flags">selection flags</link>.</entry>
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</row>
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<row>
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<entry>&v4l2-rect;</entry>
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<entry><structfield>r</structfield></entry>
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<entry>The selection rectangle.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved[9]</structfield></entry>
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<entry>Reserved fields for future use. Drivers and applications must zero this array.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</para>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>Given buffer type <structfield>type</structfield> or
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the selection target <structfield>target</structfield> is not supported,
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or the <structfield>flags</structfield> argument is not valid.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>ERANGE</errorcode></term>
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<listitem>
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<para>It is not possible to adjust &v4l2-rect; <structfield>
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r</structfield> rectangle to satisfy all constraints given in the
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<structfield>flags</structfield> argument.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EBUSY</errorcode></term>
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<listitem>
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<para>It is not possible to apply change of the selection rectangle
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at the moment. Usually because streaming is in progress.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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