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6. vidioc-cropcap.xml

<refentry id="vidioc-cropcap">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_CROPCAP</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_CROPCAP</refname>
    <refpurpose>Information about the video cropping and scaling abilities</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_cropcap
*<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_CROPCAP</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>Applications use this function to query the cropping
limits, the pixel aspect of images and to calculate scale factors.
They set the <structfield>type</structfield> field of a v4l2_cropcap
structure to the respective buffer (stream) type and call the
<constant>VIDIOC_CROPCAP</constant> ioctl with a pointer to this
structure. Drivers fill the rest of the structure. The results are
constant except when switching the video standard. Remember this
switch can occur implicit when switching the video input or
output.</para>

    <para>This ioctl must be implemented for video capture or output devices that
support cropping and/or scaling and/or have non-square pixels, and for overlay devices.</para>

    <table pgwide="1" frame="none" id="v4l2-cropcap">
      <title>struct <structname>v4l2_cropcap</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>type</structfield></entry>
	    <entry>Type of the data stream, set by the application.
Only these types are valid here:
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>,
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant>,
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>,
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE</constant> and
<constant>V4L2_BUF_TYPE_VIDEO_OVERLAY</constant>. See <xref linkend="v4l2-buf-type" />.</entry>
	  </row>
	  <row>
	    <entry>struct <link linkend="v4l2-rect-crop">v4l2_rect</link></entry>
	    <entry><structfield>bounds</structfield></entry>
	    <entry>Defines the window within capturing or output is
possible, this may exclude for example the horizontal and vertical
blanking areas. The cropping rectangle cannot exceed these limits.
Width and height are defined in pixels, the driver writer is free to
choose origin and units of the coordinate system in the analog
domain.</entry>
	  </row>
	  <row>
	    <entry>struct <link linkend="v4l2-rect-crop">v4l2_rect</link></entry>
	    <entry><structfield>defrect</structfield></entry>
	    <entry>Default cropping rectangle, it shall cover the
"whole picture". Assuming pixel aspect 1/1 this could be for example a
640&nbsp;&times;&nbsp;480 rectangle for NTSC, a
768&nbsp;&times;&nbsp;576 rectangle for PAL and SECAM centered over
the active picture area. The same co-ordinate system as for
	    <structfield>bounds</structfield> is used.</entry>
	  </row>
	  <row>
	    <entry>&v4l2-fract;</entry>
	    <entry><structfield>pixelaspect</structfield></entry>
	    <entry><para>This is the pixel aspect (y / x) when no
scaling is applied, the ratio of the actual sampling
frequency and the frequency required to get square
pixels.</para><para>When cropping coordinates refer to square pixels,
the driver sets <structfield>pixelaspect</structfield> to 1/1. Other
common values are 54/59 for PAL and SECAM, 11/10 for NTSC sampled
according to [<xref linkend="itu601" />].</para></entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <!-- NB this table is duplicated in the overlay chapter. -->

    <table pgwide="1" frame="none" id="v4l2-rect-crop">
      <title>struct <structname>v4l2_rect</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__s32</entry>
	    <entry><structfield>left</structfield></entry>
	    <entry>Horizontal offset of the top, left corner of the
rectangle, in pixels.</entry>
	  </row>
	  <row>
	    <entry>__s32</entry>
	    <entry><structfield>top</structfield></entry>
	    <entry>Vertical offset of the top, left corner of the
rectangle, in pixels.</entry>
	  </row>
	  <row>
	    <entry>__s32</entry>
	    <entry><structfield>width</structfield></entry>
	    <entry>Width of the rectangle, in pixels.</entry>
	  </row>
	  <row>
	    <entry>__s32</entry>
	    <entry><structfield>height</structfield></entry>
	    <entry>Height of the rectangle, in pixels. Width
and height cannot be negative, the fields are signed for
hysterical reasons. <!-- video4linux-list@redhat.com
on 22 Oct 2002 subject "Re:[V4L][patches!] Re:v4l2/kernel-2.5" -->
</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    &return-value;

    <variablelist>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>The &v4l2-cropcap; <structfield>type</structfield> is
invalid.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>