Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 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 <para>The ioctls are used to query and configure selection rectangles.</para> 54 55 <para>To query the cropping (composing) rectangle set &v4l2-selection; 56 <structfield> type </structfield> field to the respective buffer type. 57 Do not use the multiplanar buffer types. Use <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant> 58 instead of <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant> and use 59 <constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant> instead of 60 <constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE</constant>. The next step is 61 setting the value of &v4l2-selection; <structfield>target</structfield> field 62 to <constant>V4L2_SEL_TGT_CROP</constant> (<constant>V4L2_SEL_TGT_COMPOSE</constant>). 63 Please refer to table <xref linkend="v4l2-selections-common" /> or <xref linkend="selection-api" /> 64 for additional targets. The <structfield>flags</structfield> and <structfield>reserved 65 </structfield> fields of &v4l2-selection; are ignored and they must be filled 66 with zeros. The driver fills the rest of the structure or 67 returns &EINVAL; if incorrect buffer type or target was used. If cropping 68 (composing) is not supported then the active rectangle is not mutable and it is 69 always equal to the bounds rectangle. Finally, the &v4l2-rect; 70 <structfield>r</structfield> rectangle is filled with the current cropping 71 (composing) coordinates. The coordinates are expressed in driver-dependent 72 units. The only exception are rectangles for images in raw formats, whose 73 coordinates are always expressed in pixels.</para> 74 75 <para>To change the cropping (composing) rectangle set the &v4l2-selection; 76 <structfield>type</structfield> field to the respective buffer type. Do not 77 use multiplanar buffers. Use <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant> 78 instead of <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant>. Use 79 <constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant> instead of 80 <constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE</constant>. The next step is 81 setting the value of &v4l2-selection; <structfield>target</structfield> to 82 <constant>V4L2_SEL_TGT_CROP</constant> (<constant>V4L2_SEL_TGT_COMPOSE</constant>). 83 Please refer to table <xref linkend="v4l2-selections-common" /> or <xref linkend="selection-api" /> 84 for additional targets. The &v4l2-rect; <structfield>r</structfield> rectangle need to be 85 set to the desired active area. Field &v4l2-selection; <structfield> reserved 86 </structfield> is ignored and must be filled with zeros. The driver may adjust 87 coordinates of the requested rectangle. An application may 88 introduce constraints to control rounding behaviour. The &v4l2-selection; 89 <structfield>flags</structfield> field must be set to one of the following: 90 91 <itemizedlist> 92 <listitem> 93 <para><constant>0</constant> - The driver can adjust the rectangle size freely 94 and shall choose a crop/compose rectangle as close as possible to the requested 95 one.</para> 96 </listitem> 97 <listitem> 98 <para><constant>V4L2_SEL_FLAG_GE</constant> - The driver is not allowed to 99 shrink the rectangle. The original rectangle must lay inside the adjusted 100 one.</para> 101 </listitem> 102 <listitem> 103 <para><constant>V4L2_SEL_FLAG_LE</constant> - The driver is not allowed to 104 enlarge the rectangle. The adjusted rectangle must lay inside the original 105 one.</para> 106 </listitem> 107 <listitem> 108 <para><constant>V4L2_SEL_FLAG_GE | V4L2_SEL_FLAG_LE</constant> - The driver 109 must choose the size exactly the same as in the requested rectangle.</para> 110 </listitem> 111 </itemizedlist> 112 113 Please refer to <xref linkend="sel-const-adjust" />. 114 115 </para> 116 117 <para> The driver may have to adjusts the requested dimensions against hardware 118 limits and other parts as the pipeline, i.e. the bounds given by the 119 capture/output window or TV display. The closest possible values of horizontal 120 and vertical offset and sizes are chosen according to following priority: 121 122 <orderedlist> 123 <listitem> 124 <para>Satisfy constraints from &v4l2-selection; <structfield>flags</structfield>.</para> 125 </listitem> 126 <listitem> 127 <para>Adjust width, height, left, and top to hardware limits and alignments.</para> 128 </listitem> 129 <listitem> 130 <para>Keep center of adjusted rectangle as close as possible to the original one.</para> 131 </listitem> 132 <listitem> 133 <para>Keep width and height as close as possible to original ones.</para> 134 </listitem> 135 <listitem> 136 <para>Keep horizontal and vertical offset as close as possible to original ones.</para> 137 </listitem> 138 </orderedlist> 139 140 On success the &v4l2-rect; <structfield>r</structfield> field contains 141 the adjusted rectangle. When the parameters are unsuitable the application may 142 modify the cropping (composing) or image parameters and repeat the cycle until 143 satisfactory parameters have been negotiated. If constraints flags have to be 144 violated at then ERANGE is returned. The error indicates that <emphasis>there 145 exist no rectangle</emphasis> that satisfies the constraints.</para> 146 147 <para>Selection targets and flags are documented in <xref 148 linkend="v4l2-selections-common"/>.</para> 149 150 <para> 151 <figure id="sel-const-adjust"> 152 <title>Size adjustments with constraint flags.</title> 153 <mediaobject> 154 <imageobject> 155 <imagedata fileref="constraints.png" format="PNG" /> 156 </imageobject> 157 <textobject> 158 <phrase>Behaviour of rectangle adjustment for different constraint 159 flags.</phrase> 160 </textobject> 161 </mediaobject> 162 </figure> 163 </para> 164 165 <para> 166 <table pgwide="1" frame="none" id="v4l2-selection"> 167 <title>struct <structname>v4l2_selection</structname></title> 168 <tgroup cols="3"> 169 &cs-str; 170 <tbody valign="top"> 171 <row> 172 <entry>__u32</entry> 173 <entry><structfield>type</structfield></entry> 174 <entry>Type of the buffer (from &v4l2-buf-type;).</entry> 175 </row> 176 <row> 177 <entry>__u32</entry> 178 <entry><structfield>target</structfield></entry> 179 <entry>Used to select between <link linkend="v4l2-selections-common"> cropping 180 and composing rectangles</link>.</entry> 181 </row> 182 <row> 183 <entry>__u32</entry> 184 <entry><structfield>flags</structfield></entry> 185 <entry>Flags controlling the selection rectangle adjustments, refer to 186 <link linkend="v4l2-selection-flags">selection flags</link>.</entry> 187 </row> 188 <row> 189 <entry>&v4l2-rect;</entry> 190 <entry><structfield>r</structfield></entry> 191 <entry>The selection rectangle.</entry> 192 </row> 193 <row> 194 <entry>__u32</entry> 195 <entry><structfield>reserved[9]</structfield></entry> 196 <entry>Reserved fields for future use. Drivers and applications must zero this array.</entry> 197 </row> 198 </tbody> 199 </tgroup> 200 </table> 201 </para> 202 </refsect1> 203 204 <refsect1> 205 &return-value; 206 <variablelist> 207 <varlistentry> 208 <term><errorcode>EINVAL</errorcode></term> 209 <listitem> 210 <para>Given buffer type <structfield>type</structfield> or 211 the selection target <structfield>target</structfield> is not supported, 212 or the <structfield>flags</structfield> argument is not valid.</para> 213 </listitem> 214 </varlistentry> 215 <varlistentry> 216 <term><errorcode>ERANGE</errorcode></term> 217 <listitem> 218 <para>It is not possible to adjust &v4l2-rect; <structfield> 219 r</structfield> rectangle to satisfy all constraints given in the 220 <structfield>flags</structfield> argument.</para> 221 </listitem> 222 </varlistentry> 223 <varlistentry> 224 <term><errorcode>EBUSY</errorcode></term> 225 <listitem> 226 <para>It is not possible to apply change of the selection rectangle 227 at the moment. Usually because streaming is in progress.</para> 228 </listitem> 229 </varlistentry> 230 </variablelist> 231 </refsect1> 232 233 </refentry>
