Based on kernel version 3.0.4. Page generated on 2011-10-03 22:07 EST.
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 61 applications 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 64 with a pointer to this structure. The driver fills the rest of the 65 structure 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 71 structure.</para> 72 73 <para>The driver first adjusts the requested dimensions against 74 hardware limits, &ie; the bounds given by the capture/output window, 75 and it rounds to the closest possible values of horizontal and 76 vertical offset, width and height. In particular the driver must round 77 the vertical offset of the cropping rectangle to frame lines modulo 78 two, such that the field order cannot be confused.</para> 79 80 <para>Second the driver adjusts the image size (the opposite 81 rectangle of the scaling process, source or target depending on the 82 data direction) to the closest size possible while maintaining the 83 current horizontal and vertical scaling factor.</para> 84 85 <para>Finally the driver programs the hardware with the actual 86 cropping and image parameters. <constant>VIDIOC_S_CROP</constant> is a 87 write-only ioctl, it does not return the actual parameters. To query 88 them applications must call <constant>VIDIOC_G_CROP</constant> and 89 &VIDIOC-G-FMT;. When the parameters are unsuitable the application may 90 modify the cropping or image parameters and repeat the cycle until 91 satisfactory parameters have been negotiated.</para> 92 93 <para>When cropping is not supported then no parameters are 94 changed 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. 106 Only 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 109 defined) types with code <constant>V4L2_BUF_TYPE_PRIVATE</constant> 110 and 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 116 for &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> 136 137 <!-- 138 Local Variables: 139 mode: sgml 140 sgml-parent-document: "v4l2.sgml" 141 indent-tabs-mode: nil 142 End: 143 -->
