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143 lines
4.6 KiB
143 lines
4.6 KiB
<refentry id="vidioc-g-crop">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_G_CROP, VIDIOC_S_CROP</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_G_CROP</refname>
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<refname>VIDIOC_S_CROP</refname>
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<refpurpose>Get or set the current cropping rectangle</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_crop *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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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>const struct v4l2_crop *<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_CROP, VIDIOC_S_CROP</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>To query the cropping rectangle size and position
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applications set the <structfield>type</structfield> field of a
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<structname>v4l2_crop</structname> structure to the respective buffer
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(stream) type and call the <constant>VIDIOC_G_CROP</constant> ioctl
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with a pointer to this structure. The driver fills the rest of the
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structure or returns the &EINVAL; if cropping is not supported.</para>
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<para>To change the cropping rectangle applications initialize the
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<structfield>type</structfield> and &v4l2-rect; substructure named
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<structfield>c</structfield> of a v4l2_crop structure and call the
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<constant>VIDIOC_S_CROP</constant> ioctl with a pointer to this
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structure.</para>
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<para>The driver first adjusts the requested dimensions against
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hardware limits, &ie; the bounds given by the capture/output window,
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and it rounds to the closest possible values of horizontal and
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vertical offset, width and height. In particular the driver must round
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the vertical offset of the cropping rectangle to frame lines modulo
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two, such that the field order cannot be confused.</para>
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<para>Second the driver adjusts the image size (the opposite
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rectangle of the scaling process, source or target depending on the
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data direction) to the closest size possible while maintaining the
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current horizontal and vertical scaling factor.</para>
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<para>Finally the driver programs the hardware with the actual
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cropping and image parameters. <constant>VIDIOC_S_CROP</constant> is a
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write-only ioctl, it does not return the actual parameters. To query
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them applications must call <constant>VIDIOC_G_CROP</constant> and
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&VIDIOC-G-FMT;. When the parameters are unsuitable the application may
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modify the cropping or image parameters and repeat the cycle until
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satisfactory parameters have been negotiated.</para>
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<para>When cropping is not supported then no parameters are
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changed and <constant>VIDIOC_S_CROP</constant> returns the
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&EINVAL;.</para>
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<table pgwide="1" frame="none" id="v4l2-crop">
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<title>struct <structname>v4l2_crop</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>&v4l2-buf-type;</entry>
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<entry><structfield>type</structfield></entry>
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<entry>Type of the data stream, set by the application.
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Only these types are valid here: <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>,
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<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>,
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<constant>V4L2_BUF_TYPE_VIDEO_OVERLAY</constant>, and custom (driver
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defined) types with code <constant>V4L2_BUF_TYPE_PRIVATE</constant>
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and higher.</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>c</structfield></entry>
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<entry>Cropping rectangle. The same co-ordinate system as
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for &v4l2-cropcap; <structfield>bounds</structfield> is used.</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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</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>Cropping is not supported.</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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<!--
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Local Variables:
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mode: sgml
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sgml-parent-document: "v4l2.sgml"
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indent-tabs-mode: nil
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End:
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-->
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