Based on kernel version 3.0.4. Page generated on 2011-10-03 22:07 EST.
1 <refentry id="vidioc-cropcap"> 2 <refmeta> 3 <refentrytitle>ioctl VIDIOC_CROPCAP</refentrytitle> 4 &manvol; 5 </refmeta> 6 7 <refnamediv> 8 <refname>VIDIOC_CROPCAP</refname> 9 <refpurpose>Information about the video cropping and scaling abilities</refpurpose> 10 </refnamediv> 11 12 <refsynopsisdiv> 13 <funcsynopsis> 14 <funcprototype> 15 <funcdef>int <function>ioctl</function></funcdef> 16 <paramdef>int <parameter>fd</parameter></paramdef> 17 <paramdef>int <parameter>request</parameter></paramdef> 18 <paramdef>struct v4l2_cropcap 19 *<parameter>argp</parameter></paramdef> 20 </funcprototype> 21 </funcsynopsis> 22 </refsynopsisdiv> 23 24 <refsect1> 25 <title>Arguments</title> 26 27 <variablelist> 28 <varlistentry> 29 <term><parameter>fd</parameter></term> 30 <listitem> 31 <para>&fd;</para> 32 </listitem> 33 </varlistentry> 34 <varlistentry> 35 <term><parameter>request</parameter></term> 36 <listitem> 37 <para>VIDIOC_CROPCAP</para> 38 </listitem> 39 </varlistentry> 40 <varlistentry> 41 <term><parameter>argp</parameter></term> 42 <listitem> 43 <para></para> 44 </listitem> 45 </varlistentry> 46 </variablelist> 47 </refsect1> 48 49 <refsect1> 50 <title>Description</title> 51 52 <para>Applications use this function to query the cropping 53 limits, the pixel aspect of images and to calculate scale factors. 54 They set the <structfield>type</structfield> field of a v4l2_cropcap 55 structure to the respective buffer (stream) type and call the 56 <constant>VIDIOC_CROPCAP</constant> ioctl with a pointer to this 57 structure. Drivers fill the rest of the structure. The results are 58 constant except when switching the video standard. Remember this 59 switch can occur implicit when switching the video input or 60 output.</para> 61 62 <table pgwide="1" frame="none" id="v4l2-cropcap"> 63 <title>struct <structname>v4l2_cropcap</structname></title> 64 <tgroup cols="3"> 65 &cs-str; 66 <tbody valign="top"> 67 <row> 68 <entry>&v4l2-buf-type;</entry> 69 <entry><structfield>type</structfield></entry> 70 <entry>Type of the data stream, set by the application. 71 Only these types are valid here: 72 <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>, 73 <constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>, 74 <constant>V4L2_BUF_TYPE_VIDEO_OVERLAY</constant>, and custom (driver 75 defined) types with code <constant>V4L2_BUF_TYPE_PRIVATE</constant> 76 and higher.</entry> 77 </row> 78 <row> 79 <entry>struct <link linkend="v4l2-rect-crop">v4l2_rect</link></entry> 80 <entry><structfield>bounds</structfield></entry> 81 <entry>Defines the window within capturing or output is 82 possible, this may exclude for example the horizontal and vertical 83 blanking areas. The cropping rectangle cannot exceed these limits. 84 Width and height are defined in pixels, the driver writer is free to 85 choose origin and units of the coordinate system in the analog 86 domain.</entry> 87 </row> 88 <row> 89 <entry>struct <link linkend="v4l2-rect-crop">v4l2_rect</link></entry> 90 <entry><structfield>defrect</structfield></entry> 91 <entry>Default cropping rectangle, it shall cover the 92 "whole picture". Assuming pixel aspect 1/1 this could be for example a 93 640 × 480 rectangle for NTSC, a 94 768 × 576 rectangle for PAL and SECAM centered over 95 the active picture area. The same co-ordinate system as for 96 <structfield>bounds</structfield> is used.</entry> 97 </row> 98 <row> 99 <entry>&v4l2-fract;</entry> 100 <entry><structfield>pixelaspect</structfield></entry> 101 <entry><para>This is the pixel aspect (y / x) when no 102 scaling is applied, the ratio of the actual sampling 103 frequency and the frequency required to get square 104 pixels.</para><para>When cropping coordinates refer to square pixels, 105 the driver sets <structfield>pixelaspect</structfield> to 1/1. Other 106 common values are 54/59 for PAL and SECAM, 11/10 for NTSC sampled 107 according to [<xref linkend="itu601" />].</para></entry> 108 </row> 109 </tbody> 110 </tgroup> 111 </table> 112 113 <!-- NB this table is duplicated in the overlay chapter. --> 114 115 <table pgwide="1" frame="none" id="v4l2-rect-crop"> 116 <title>struct <structname>v4l2_rect</structname></title> 117 <tgroup cols="3"> 118 &cs-str; 119 <tbody valign="top"> 120 <row> 121 <entry>__s32</entry> 122 <entry><structfield>left</structfield></entry> 123 <entry>Horizontal offset of the top, left corner of the 124 rectangle, in pixels.</entry> 125 </row> 126 <row> 127 <entry>__s32</entry> 128 <entry><structfield>top</structfield></entry> 129 <entry>Vertical offset of the top, left corner of the 130 rectangle, in pixels.</entry> 131 </row> 132 <row> 133 <entry>__s32</entry> 134 <entry><structfield>width</structfield></entry> 135 <entry>Width of the rectangle, in pixels.</entry> 136 </row> 137 <row> 138 <entry>__s32</entry> 139 <entry><structfield>height</structfield></entry> 140 <entry>Height of the rectangle, in pixels. Width 141 and height cannot be negative, the fields are signed for 142 hysterical reasons. <!-- video4linux-list@redhat.com 143 on 22 Oct 2002 subject "Re:[V4L][patches!] Re:v4l2/kernel-2.5" --> 144 </entry> 145 </row> 146 </tbody> 147 </tgroup> 148 </table> 149 </refsect1> 150 151 <refsect1> 152 &return-value; 153 154 <variablelist> 155 <varlistentry> 156 <term><errorcode>EINVAL</errorcode></term> 157 <listitem> 158 <para>The &v4l2-cropcap; <structfield>type</structfield> is 159 invalid or the ioctl is not supported. This is not permitted for 160 video capture, output and overlay devices, which must support 161 <constant>VIDIOC_CROPCAP</constant>.</para> 162 </listitem> 163 </varlistentry> 164 </variablelist> 165 </refsect1> 166 </refentry> 167 168 <!-- 169 Local Variables: 170 mode: sgml 171 sgml-parent-document: "v4l2.sgml" 172 indent-tabs-mode: nil 173 End: 174 -->
