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
53limits, the pixel aspect of images and to calculate scale factors.
54They set the <structfield>type</structfield> field of a v4l2_cropcap
55structure to the respective buffer (stream) type and call the
56<constant>VIDIOC_CROPCAP</constant> ioctl with a pointer to this
57structure. Drivers fill the rest of the structure. The results are
58constant except when switching the video standard. Remember this
59switch can occur implicit when switching the video input or
60output.</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.
71Only 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
75defined) types with code <constant>V4L2_BUF_TYPE_PRIVATE</constant>
76and 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
82possible, this may exclude for example the horizontal and vertical
83blanking areas. The cropping rectangle cannot exceed these limits.
84Width and height are defined in pixels, the driver writer is free to
85choose origin and units of the coordinate system in the analog
86domain.</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
93640&nbsp;&times;&nbsp;480 rectangle for NTSC, a
94768&nbsp;&times;&nbsp;576 rectangle for PAL and SECAM centered over
95the 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
102scaling is applied, the ratio of the actual sampling
103frequency and the frequency required to get square
104pixels.</para><para>When cropping coordinates refer to square pixels,
105the driver sets <structfield>pixelaspect</structfield> to 1/1. Other
106common values are 54/59 for PAL and SECAM, 11/10 for NTSC sampled
107according 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
124rectangle, 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
130rectangle, 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
141and height cannot be negative, the fields are signed for
142hysterical reasons. <!-- video4linux-list@redhat.com
143on 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
159invalid. This is not permitted for video capture, output and overlay devices,
160which must support <constant>VIDIOC_CROPCAP</constant>.</para>
161	</listitem>
162      </varlistentry>
163    </variablelist>
164  </refsect1>
165</refentry>
166