Documentation/DocBook/media/v4l/vidioc-g-selection.xml

   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 <structfield>
  62 &v4l2-selection;::type </structfield> to the respective buffer type.  Do not
  63 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 <structfield> &v4l2-selection;::target </structfield> to value
  68 <constant> V4L2_SEL_TGT_CROP_ACTIVE </constant> (<constant>
  69 V4L2_SEL_TGT_COMPOSE_ACTIVE </constant>).  Please refer to table <xref
  70 linkend="v4l2-sel-target" /> or <xref linkend="selection-api" /> for additional
  71 targets.  Fields <structfield> &v4l2-selection;::flags </structfield> and
  72 <structfield> &v4l2-selection;::reserved </structfield> are ignored and they
  73 must be filled 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, structure <structfield>
  77 &v4l2-selection;::r </structfield> 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 <structfield>
  83 &v4l2-selection;::type </structfield> 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 <structfield> &v4l2-selection;::target </structfield> to value
  89 <constant> V4L2_SEL_TGT_CROP_ACTIVE </constant> (<constant>
  90 V4L2_SEL_TGT_COMPOSE_ACTIVE </constant>). Please refer to table <xref
  91 linkend="v4l2-sel-target" /> or <xref linkend="selection-api" /> for additional
  92 targets.  Set desired active area into the field <structfield>
  93 &v4l2-selection;::r </structfield>.  Field <structfield>
  94 &v4l2-selection;::reserved </structfield> is ignored and must be filled with
  95 zeros.  The driver may adjust the rectangle coordinates. An application may
  96 introduce constraints to control rounding behaviour. Set the field
  97 <structfield> &v4l2-selection;::flags </structfield> to one of values:
  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 <structfield>&v4l2-selection;::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 field <structfield> &v4l2-selection;::r </structfield> 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   </refsect1>
 156
 157   <refsect1>
 158     <table frame="none" pgwide="1" id="v4l2-sel-target">
 159       <title>Selection targets.</title>
 160       <tgroup cols="3">
 161         &cs-def;
 162         <tbody valign="top">
 163           <row>
 164             <entry><constant>V4L2_SEL_TGT_CROP_ACTIVE</constant></entry>
 165             <entry>0</entry>
 166             <entry>area that is currently cropped by hardware</entry>
 167           </row>
 168           <row>
 169             <entry><constant>V4L2_SEL_TGT_CROP_DEFAULT</constant></entry>
 170             <entry>1</entry>
 171             <entry>suggested cropping rectangle that covers the "whole picture"</entry>
 172           </row>
 173           <row>
 174             <entry><constant>V4L2_SEL_TGT_CROP_BOUNDS</constant></entry>
 175             <entry>2</entry>
 176             <entry>limits for the cropping rectangle</entry>
 177           </row>
 178           <row>
 179             <entry><constant>V4L2_SEL_TGT_COMPOSE_ACTIVE</constant></entry>
 180             <entry>256</entry>
 181             <entry>area to which data are composed by hardware</entry>
 182           </row>
 183           <row>
 184             <entry><constant>V4L2_SEL_TGT_COMPOSE_DEFAULT</constant></entry>
 185             <entry>257</entry>
 186             <entry>suggested composing rectangle that covers the "whole picture"</entry>
 187           </row>
 188           <row>
 189             <entry><constant>V4L2_SEL_TGT_COMPOSE_BOUNDS</constant></entry>
 190             <entry>258</entry>
 191             <entry>limits for the composing rectangle</entry>
 192           </row>
 193           <row>
 194             <entry><constant>V4L2_SEL_TGT_COMPOSE_PADDED</constant></entry>
 195             <entry>259</entry>
 196             <entry>the active area and all padding pixels that are inserted or modified by the hardware</entry>
 197           </row>
 198         </tbody>
 199       </tgroup>
 200     </table>
 201   </refsect1>
 202
 203   <refsect1>
 204     <table frame="none" pgwide="1" id="v4l2-sel-flags">
 205       <title>Selection constraint flags</title>
 206       <tgroup cols="3">
 207         &cs-def;
 208         <tbody valign="top">
 209           <row>
 210             <entry><constant>V4L2_SEL_FLAG_GE</constant></entry>
 211             <entry>0x00000001</entry>
 212             <entry>indicate that adjusted rectangle must contain a rectangle from <structfield>&v4l2-selection;::r</structfield></entry>
 213           </row>
 214           <row>
 215             <entry><constant>V4L2_SEL_FLAG_LE</constant></entry>
 216             <entry>0x00000002</entry>
 217             <entry>indicate that adjusted rectangle must be inside a rectangle from <structfield>&v4l2-selection;::r</structfield></entry>
 218           </row>
 219         </tbody>
 220       </tgroup>
 221     </table>
 222   </refsect1>
 223
 224     <section>
 225       <figure id="sel-const-adjust">
 226         <title>Size adjustments with constraint flags.</title>
 227         <mediaobject>
 228           <imageobject>
 229             <imagedata fileref="constraints.png" format="PNG" />
 230           </imageobject>
 231           <textobject>
 232             <phrase>Behaviour of rectangle adjustment for different constraint
 233             flags.</phrase>
 234           </textobject>
 235         </mediaobject>
 236       </figure>
 237     </section>
 238
 239   <refsect1>
 240     <table pgwide="1" frame="none" id="v4l2-selection">
 241       <title>struct <structname>v4l2_selection</structname></title>
 242       <tgroup cols="3">
 243         &cs-str;
 244         <tbody valign="top">
 245           <row>
 246             <entry>__u32</entry>
 247             <entry><structfield>type</structfield></entry>
 248             <entry>Type of the buffer (from &v4l2-buf-type;)</entry>
 249           </row>
 250           <row>
 251             <entry>__u32</entry>
 252             <entry><structfield>target</structfield></entry>
 253             <entry>used to select between <link linkend="v4l2-sel-target"> cropping and composing rectangles </link></entry>
 254           </row>
 255           <row>
 256             <entry>__u32</entry>
 257             <entry><structfield>flags</structfield></entry>
 258             <entry>control over coordinates adjustments, refer to <link linkend="v4l2-sel-flags">selection flags</link></entry>
 259           </row>
 260           <row>
 261             <entry>&v4l2-rect;</entry>
 262             <entry><structfield>r</structfield></entry>
 263             <entry>selection rectangle</entry>
 264           </row>
 265           <row>
 266             <entry>__u32</entry>
 267             <entry><structfield>reserved[9]</structfield></entry>
 268             <entry>Reserved fields for future use</entry>
 269           </row>
 270         </tbody>
 271       </tgroup>
 272     </table>
 273   </refsect1>
 274
 275   <refsect1>
 276     &return-value;
 277     <variablelist>
 278       <varlistentry>
 279         <term><errorcode>EINVAL</errorcode></term>
 280         <listitem>
 281           <para>The buffer <structfield> &v4l2-selection;::type </structfield>
 282 or <structfield> &v4l2-selection;::target </structfield> is not supported, or
 283 the <structfield> &v4l2-selection;::flags </structfield> are invalid.</para>
 284         </listitem>
 285       </varlistentry>
 286       <varlistentry>
 287         <term><errorcode>ERANGE</errorcode></term>
 288         <listitem>
 289           <para>it is not possible to adjust a rectangle <structfield>
 290 &v4l2-selection;::r </structfield> that satisfies all contraints from
 291 <structfield> &v4l2-selection;::flags </structfield>.</para>
 292         </listitem>
 293       </varlistentry>
 294       <varlistentry>
 295         <term><errorcode>EBUSY</errorcode></term>
 296         <listitem>
 297           <para>it is not possible to apply change of selection rectangle at the moment.
 298 Usually because streaming is in progress.</para>
 299         </listitem>
 300       </varlistentry>
 301     </variablelist>
 302   </refsect1>
 303
 304 </refentry>