/Documentation/DocBook/v4l/vidioc-g-crop.xml

  1<refentry id="vidioc-g-crop">
  2  <refmeta>
  3    <refentrytitle>ioctl VIDIOC_G_CROP, VIDIOC_S_CROP</refentrytitle>
  4    &manvol;
  5  </refmeta>
  6
  7  <refnamediv>
  8    <refname>VIDIOC_G_CROP</refname>
  9    <refname>VIDIOC_S_CROP</refname>
 10    <refpurpose>Get or set the current cropping rectangle</refpurpose>
 11  </refnamediv>
 12
 13  <refsynopsisdiv>
 14    <funcsynopsis>
 15      <funcprototype>
 16	<funcdef>int <function>ioctl</function></funcdef>
 17	<paramdef>int <parameter>fd</parameter></paramdef>
 18	<paramdef>int <parameter>request</parameter></paramdef>
 19	<paramdef>struct v4l2_crop *<parameter>argp</parameter></paramdef>
 20      </funcprototype>
 21    </funcsynopsis>
 22    <funcsynopsis>
 23      <funcprototype>
 24	<funcdef>int <function>ioctl</function></funcdef>
 25	<paramdef>int <parameter>fd</parameter></paramdef>
 26	<paramdef>int <parameter>request</parameter></paramdef>
 27	<paramdef>const struct v4l2_crop *<parameter>argp</parameter></paramdef>
 28      </funcprototype>
 29    </funcsynopsis>
 30  </refsynopsisdiv>
 31
 32  <refsect1>
 33    <title>Arguments</title>
 34
 35    <variablelist>
 36      <varlistentry>
 37	<term><parameter>fd</parameter></term>
 38	<listitem>
 39	  <para>&fd;</para>
 40	</listitem>
 41      </varlistentry>
 42      <varlistentry>
 43	<term><parameter>request</parameter></term>
 44	<listitem>
 45	  <para>VIDIOC_G_CROP, VIDIOC_S_CROP</para>
 46	</listitem>
 47      </varlistentry>
 48      <varlistentry>
 49	<term><parameter>argp</parameter></term>
 50	<listitem>
 51	  <para></para>
 52	</listitem>
 53      </varlistentry>
 54    </variablelist>
 55  </refsect1>
 56
 57  <refsect1>
 58    <title>Description</title>
 59
 60    <para>To query the cropping rectangle size and position
 61applications set the <structfield>type</structfield> field of a
 62<structname>v4l2_crop</structname> structure to the respective buffer
 63(stream) type and call the <constant>VIDIOC_G_CROP</constant> ioctl
 64with a pointer to this structure. The driver fills the rest of the
 65structure or returns the &EINVAL; if cropping is not supported.</para>
 66
 67    <para>To change the cropping rectangle applications initialize the
 68<structfield>type</structfield> and &v4l2-rect; substructure named
 69<structfield>c</structfield> of a v4l2_crop structure and call the
 70<constant>VIDIOC_S_CROP</constant> ioctl with a pointer to this
 71structure.</para>
 72
 73    <para>The driver first adjusts the requested dimensions against
 74hardware limits, &ie; the bounds given by the capture/output window,
 75and it rounds to the closest possible values of horizontal and
 76vertical offset, width and height. In particular the driver must round
 77the vertical offset of the cropping rectangle to frame lines modulo
 78two, such that the field order cannot be confused.</para>
 79
 80    <para>Second the driver adjusts the image size (the opposite
 81rectangle of the scaling process, source or target depending on the
 82data direction) to the closest size possible while maintaining the
 83current horizontal and vertical scaling factor.</para>
 84
 85    <para>Finally the driver programs the hardware with the actual
 86cropping and image parameters. <constant>VIDIOC_S_CROP</constant> is a
 87write-only ioctl, it does not return the actual parameters. To query
 88them applications must call <constant>VIDIOC_G_CROP</constant> and
 89&VIDIOC-G-FMT;. When the parameters are unsuitable the application may
 90modify the cropping or image parameters and repeat the cycle until
 91satisfactory parameters have been negotiated.</para>
 92
 93    <para>When cropping is not supported then no parameters are
 94changed and <constant>VIDIOC_S_CROP</constant> returns the
 95&EINVAL;.</para>
 96
 97    <table pgwide="1" frame="none" id="v4l2-crop">
 98      <title>struct <structname>v4l2_crop</structname></title>
 99      <tgroup cols="3">
100	&cs-str;
101	<tbody valign="top">
102	  <row>
103	    <entry>&v4l2-buf-type;</entry>
104	    <entry><structfield>type</structfield></entry>
105	    <entry>Type of the data stream, set by the application.
106Only these types are valid here: <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>,
107<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>,
108<constant>V4L2_BUF_TYPE_VIDEO_OVERLAY</constant>, and custom (driver
109defined) types with code <constant>V4L2_BUF_TYPE_PRIVATE</constant>
110and higher.</entry>
111	  </row>
112	  <row>
113	    <entry>&v4l2-rect;</entry>
114	    <entry><structfield>c</structfield></entry>
115	    <entry>Cropping rectangle. The same co-ordinate system as
116for &v4l2-cropcap; <structfield>bounds</structfield> is used.</entry>
117	  </row>
118	</tbody>
119      </tgroup>
120    </table>
121  </refsect1>
122
123  <refsect1>
124    &return-value;
125
126    <variablelist>
127      <varlistentry>
128	<term><errorcode>EINVAL</errorcode></term>
129	<listitem>
130	  <para>Cropping is not supported.</para>
131	</listitem>
132      </varlistentry>
133    </variablelist>
134  </refsect1>
135</refentry>
136
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