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Based on kernel version 3.13. Page generated on 2014-01-20 22:02 EST.

1	<refentry id="vidioc-g-selection">
2	
3	  <refmeta>
4	    <refentrytitle>ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION</refentrytitle>
5	    &manvol;
6	  </refmeta>
7	
8	  <refnamediv>
9	    <refname>VIDIOC_G_SELECTION</refname>
10	    <refname>VIDIOC_S_SELECTION</refname>
11	    <refpurpose>Get or set one of the selection rectangles</refpurpose>
12	  </refnamediv>
13	
14	  <refsynopsisdiv>
15	    <funcsynopsis>
16	      <funcprototype>
17		<funcdef>int <function>ioctl</function></funcdef>
18		<paramdef>int <parameter>fd</parameter></paramdef>
19		<paramdef>int <parameter>request</parameter></paramdef>
20		<paramdef>struct v4l2_selection *<parameter>argp</parameter></paramdef>
21	      </funcprototype>
22	    </funcsynopsis>
23	  </refsynopsisdiv>
24	
25	  <refsect1>
26	    <title>Arguments</title>
27	
28	    <variablelist>
29	      <varlistentry>
30		<term><parameter>fd</parameter></term>
31		<listitem>
32		  <para>&fd;</para>
33		</listitem>
34	      </varlistentry>
35	      <varlistentry>
36		<term><parameter>request</parameter></term>
37		<listitem>
38		  <para>VIDIOC_G_SELECTION, VIDIOC_S_SELECTION</para>
39		</listitem>
40	      </varlistentry>
41	      <varlistentry>
42		<term><parameter>argp</parameter></term>
43		<listitem>
44		  <para></para>
45		</listitem>
46	      </varlistentry>
47	    </variablelist>
48	  </refsect1>
49	
50	  <refsect1>
51	    <title>Description</title>
52	
53	    <note>
54	      <title>Experimental</title>
55	      <para>This is an <link linkend="experimental"> experimental </link>
56	      interface and may change in the future.</para>
57	    </note>
58	
59	    <para>The ioctls are used to query and configure selection rectangles.</para>
60	
61	<para> To query the cropping (composing) rectangle set &v4l2-selection;
62	<structfield> type </structfield> field to the respective buffer type.
63	Do not use multiplanar buffers.  Use <constant> V4L2_BUF_TYPE_VIDEO_CAPTURE
64	</constant> instead of <constant> V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE
65	</constant>.  Use <constant> V4L2_BUF_TYPE_VIDEO_OUTPUT </constant> instead of
66	<constant> V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE </constant>.  The next step is
67	setting the value of &v4l2-selection; <structfield>target</structfield> field
68	to <constant> V4L2_SEL_TGT_CROP </constant> (<constant>
69	V4L2_SEL_TGT_COMPOSE </constant>).  Please refer to table <xref
70	linkend="v4l2-selections-common" /> or <xref linkend="selection-api" /> for additional
71	targets.  The <structfield>flags</structfield> and <structfield>reserved
72	</structfield> fields of &v4l2-selection; are ignored and they must be filled
73	with zeros.  The driver fills the rest of the structure or
74	returns &EINVAL; if incorrect buffer type or target was used. If cropping
75	(composing) is not supported then the active rectangle is not mutable and it is
76	always equal to the bounds rectangle.  Finally, the &v4l2-rect;
77	<structfield>r</structfield> rectangle is filled with the current cropping
78	(composing) coordinates. The coordinates are expressed in driver-dependent
79	units. The only exception are rectangles for images in raw formats, whose
80	coordinates are always expressed in pixels.  </para>
81	
82	<para> To change the cropping (composing) rectangle set the &v4l2-selection;
83	<structfield>type</structfield> field to the respective buffer type.  Do not
84	use multiplanar buffers.  Use <constant> V4L2_BUF_TYPE_VIDEO_CAPTURE
85	</constant> instead of <constant> V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE
86	</constant>.  Use <constant> V4L2_BUF_TYPE_VIDEO_OUTPUT </constant> instead of
87	<constant> V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE </constant>.  The next step is
88	setting the value of &v4l2-selection; <structfield>target</structfield> to
89	<constant>V4L2_SEL_TGT_CROP</constant> (<constant>
90	V4L2_SEL_TGT_COMPOSE </constant>). Please refer to table <xref
91	linkend="v4l2-selections-common" /> or <xref linkend="selection-api" /> for additional
92	targets.  The &v4l2-rect; <structfield>r</structfield> rectangle need to be
93	set to the desired active area. Field &v4l2-selection; <structfield> reserved
94	</structfield> is ignored and must be filled with zeros.  The driver may adjust
95	coordinates of the requested rectangle. An application may
96	introduce constraints to control rounding behaviour. The &v4l2-selection;
97	<structfield>flags</structfield> field must be set to one of the following:
98	
99	<itemizedlist>
100	  <listitem>
101	<para><constant>0</constant> - The driver can adjust the rectangle size freely
102	and shall choose a crop/compose rectangle as close as possible to the requested
103	one.</para>
104	  </listitem>
105	  <listitem>
106	<para><constant>V4L2_SEL_FLAG_GE</constant> - The driver is not allowed to
107	shrink the rectangle.  The original rectangle must lay inside the adjusted
108	one.</para>
109	  </listitem>
110	  <listitem>
111	<para><constant>V4L2_SEL_FLAG_LE</constant> - The driver is not allowed to
112	enlarge the rectangle.  The adjusted rectangle must lay inside the original
113	one.</para>
114	  </listitem>
115	  <listitem>
116	<para><constant>V4L2_SEL_FLAG_GE | V4L2_SEL_FLAG_LE</constant> - The driver
117	must choose the size exactly the same as in the requested rectangle.</para>
118	  </listitem>
119	</itemizedlist>
120	
121	Please refer to <xref linkend="sel-const-adjust" />.
122	
123	</para>
124	
125	<para> The driver may have to adjusts the requested dimensions against hardware
126	limits and other parts as the pipeline, i.e. the bounds given by the
127	capture/output window or TV display. The closest possible values of horizontal
128	and vertical offset and sizes are chosen according to following priority:
129	
130	<orderedlist>
131	  <listitem>
132	    <para>Satisfy constraints from &v4l2-selection; <structfield>flags</structfield>.</para>
133	  </listitem>
134	  <listitem>
135	    <para>Adjust width, height, left, and top to hardware limits and alignments.</para>
136	  </listitem>
137	  <listitem>
138	    <para>Keep center of adjusted rectangle as close as possible to the original one.</para>
139	  </listitem>
140	  <listitem>
141	    <para>Keep width and height as close as possible to original ones.</para>
142	  </listitem>
143	  <listitem>
144	    <para>Keep horizontal and vertical offset as close as possible to original ones.</para>
145	  </listitem>
146	</orderedlist>
147	
148	On success the &v4l2-rect; <structfield>r</structfield> field contains
149	the adjusted rectangle. When the parameters are unsuitable the application may
150	modify the cropping (composing) or image parameters and repeat the cycle until
151	satisfactory parameters have been negotiated. If constraints flags have to be
152	violated at then ERANGE is returned. The error indicates that <emphasis> there
153	exist no rectangle </emphasis> that satisfies the constraints.</para>
154	
155	  <para>Selection targets and flags are documented in <xref
156	  linkend="v4l2-selections-common"/>.</para>
157	
158	    <para>
159	      <figure id="sel-const-adjust">
160		<title>Size adjustments with constraint flags.</title>
161		<mediaobject>
162		  <imageobject>
163		    <imagedata fileref="constraints.png" format="PNG" />
164		  </imageobject>
165		  <textobject>
166		    <phrase>Behaviour of rectangle adjustment for different constraint
167	            flags.</phrase>
168		  </textobject>
169		</mediaobject>
170	      </figure>
171	    </para>
172	
173	  <para>
174	    <table pgwide="1" frame="none" id="v4l2-selection">
175	      <title>struct <structname>v4l2_selection</structname></title>
176	      <tgroup cols="3">
177		&cs-str;
178		<tbody valign="top">
179		  <row>
180		    <entry>__u32</entry>
181		    <entry><structfield>type</structfield></entry>
182		    <entry>Type of the buffer (from &v4l2-buf-type;).</entry>
183		  </row>
184		  <row>
185		    <entry>__u32</entry>
186		    <entry><structfield>target</structfield></entry>
187	            <entry>Used to select between <link linkend="v4l2-selections-common"> cropping
188		    and composing rectangles</link>.</entry>
189		  </row>
190		  <row>
191		    <entry>__u32</entry>
192		    <entry><structfield>flags</structfield></entry>
193	            <entry>Flags controlling the selection rectangle adjustments, refer to
194		    <link linkend="v4l2-selection-flags">selection flags</link>.</entry>
195		  </row>
196		  <row>
197		    <entry>&v4l2-rect;</entry>
198		    <entry><structfield>r</structfield></entry>
199		    <entry>The selection rectangle.</entry>
200		  </row>
201		  <row>
202		    <entry>__u32</entry>
203		    <entry><structfield>reserved[9]</structfield></entry>
204		    <entry>Reserved fields for future use.</entry>
205		  </row>
206		</tbody>
207	      </tgroup>
208	    </table>
209	  </para>
210	  </refsect1>
211	
212	  <refsect1>
213	    &return-value;
214	    <variablelist>
215	      <varlistentry>
216		<term><errorcode>EINVAL</errorcode></term>
217		<listitem>
218		  <para>Given buffer type <structfield>type</structfield> or
219	the selection target <structfield>target</structfield> is not supported,
220	or the <structfield>flags</structfield> argument is not valid.</para>
221		</listitem>
222	      </varlistentry>
223	      <varlistentry>
224		<term><errorcode>ERANGE</errorcode></term>
225		<listitem>
226		  <para>It is not possible to adjust &v4l2-rect; <structfield>
227	r</structfield> rectangle to satisfy all contraints given in the
228	<structfield>flags</structfield> argument.</para>
229		</listitem>
230	      </varlistentry>
231	      <varlistentry>
232		<term><errorcode>EBUSY</errorcode></term>
233		<listitem>
234		  <para>It is not possible to apply change of the selection rectangle
235	at the moment. Usually because streaming is in progress.</para>
236		</listitem>
237	      </varlistentry>
238	    </variablelist>
239	  </refsect1>
240	
241	</refentry>
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