Documentation/linux_tv/media/v4l/vidioc-g-selection.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _VIDIOC_G_SELECTION:
   4
   5 ********************************************
   6 ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION
   7 ********************************************
   8
   9 *man VIDIOC_G_SELECTION(2)*
  10
  11 VIDIOC_S_SELECTION
  12 Get or set one of the selection rectangles
  13
  14
  15 Synopsis
  16 ========
  17
  18 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_selection *argp )
  19
  20 Arguments
  21 =========
  22
  23 ``fd``
  24     File descriptor returned by :ref:`open() <func-open>`.
  25
  26 ``request``
  27     VIDIOC_G_SELECTION, VIDIOC_S_SELECTION
  28
  29 ``argp``
  30
  31
  32 Description
  33 ===========
  34
  35 The ioctls are used to query and configure selection rectangles.
  36
  37 To query the cropping (composing) rectangle set struct
  38 :ref:`v4l2_selection <v4l2-selection>` ``type`` field to the
  39 respective buffer type. Do not use the multiplanar buffer types. Use
  40 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` instead of
  41 ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and use
  42 ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` instead of
  43 ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``. The next step is setting the
  44 value of struct :ref:`v4l2_selection <v4l2-selection>` ``target``
  45 field to ``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer
  46 to table :ref:`v4l2-selections-common` or :ref:`selection-api` for
  47 additional targets. The ``flags`` and ``reserved`` fields of struct
  48 :ref:`v4l2_selection <v4l2-selection>` are ignored and they must be
  49 filled with zeros. The driver fills the rest of the structure or returns
  50 EINVAL error code if incorrect buffer type or target was used. If
  51 cropping (composing) is not supported then the active rectangle is not
  52 mutable and it is always equal to the bounds rectangle. Finally, the
  53 struct :ref:`v4l2_rect <v4l2-rect>` ``r`` rectangle is filled with
  54 the current cropping (composing) coordinates. The coordinates are
  55 expressed in driver-dependent units. The only exception are rectangles
  56 for images in raw formats, whose coordinates are always expressed in
  57 pixels.
  58
  59 To change the cropping (composing) rectangle set the struct
  60 :ref:`v4l2_selection <v4l2-selection>` ``type`` field to the
  61 respective buffer type. Do not use multiplanar buffers. Use
  62 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` instead of
  63 ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. Use
  64 ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` instead of
  65 ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``. The next step is setting the
  66 value of struct :ref:`v4l2_selection <v4l2-selection>` ``target`` to
  67 ``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer to table
  68 :ref:`v4l2-selections-common` or :ref:`selection-api` for additional
  69 targets. The struct :ref:`v4l2_rect <v4l2-rect>` ``r`` rectangle need
  70 to be set to the desired active area. Field struct
  71 :ref:`v4l2_selection <v4l2-selection>` ``reserved`` is ignored and
  72 must be filled with zeros. The driver may adjust coordinates of the
  73 requested rectangle. An application may introduce constraints to control
  74 rounding behaviour. The struct :ref:`v4l2_selection <v4l2-selection>`
  75 ``flags`` field must be set to one of the following:
  76
  77 -  ``0`` - The driver can adjust the rectangle size freely and shall
  78    choose a crop/compose rectangle as close as possible to the requested
  79    one.
  80
  81 -  ``V4L2_SEL_FLAG_GE`` - The driver is not allowed to shrink the
  82    rectangle. The original rectangle must lay inside the adjusted one.
  83
  84 -  ``V4L2_SEL_FLAG_LE`` - The driver is not allowed to enlarge the
  85    rectangle. The adjusted rectangle must lay inside the original one.
  86
  87 -  ``V4L2_SEL_FLAG_GE | V4L2_SEL_FLAG_LE`` - The driver must choose the
  88    size exactly the same as in the requested rectangle.
  89
  90 Please refer to :ref:`sel-const-adjust`.
  91
  92 The driver may have to adjusts the requested dimensions against hardware
  93 limits and other parts as the pipeline, i.e. the bounds given by the
  94 capture/output window or TV display. The closest possible values of
  95 horizontal and vertical offset and sizes are chosen according to
  96 following priority:
  97
  98 1. Satisfy constraints from struct
  99    :ref:`v4l2_selection <v4l2-selection>` ``flags``.
 100
 101 2. Adjust width, height, left, and top to hardware limits and
 102    alignments.
 103
 104 3. Keep center of adjusted rectangle as close as possible to the
 105    original one.
 106
 107 4. Keep width and height as close as possible to original ones.
 108
 109 5. Keep horizontal and vertical offset as close as possible to original
 110    ones.
 111
 112 On success the struct :ref:`v4l2_rect <v4l2-rect>` ``r`` field
 113 contains the adjusted rectangle. When the parameters are unsuitable the
 114 application may modify the cropping (composing) or image parameters and
 115 repeat the cycle until satisfactory parameters have been negotiated. If
 116 constraints flags have to be violated at then ``ERANGE`` is returned. The
 117 error indicates that *there exist no rectangle* that satisfies the
 118 constraints.
 119
 120 Selection targets and flags are documented in
 121 :ref:`v4l2-selections-common`.
 122
 123
 124 .. _sel-const-adjust:
 125
 126 .. figure::  vidioc-g-selection_files/constraints.*
 127     :alt:    constraints.png
 128     :align:  center
 129
 130     Size adjustments with constraint flags.
 131
 132     Behaviour of rectangle adjustment for different constraint flags.
 133
 134
 135
 136
 137 .. _v4l2-selection:
 138
 139 .. flat-table:: struct v4l2_selection
 140     :header-rows:  0
 141     :stub-columns: 0
 142     :widths:       1 1 2
 143
 144
 145     -  .. row 1
 146
 147        -  __u32
 148
 149        -  ``type``
 150
 151        -  Type of the buffer (from enum
 152           :ref:`v4l2_buf_type <v4l2-buf-type>`).
 153
 154     -  .. row 2
 155
 156        -  __u32
 157
 158        -  ``target``
 159
 160        -  Used to select between
 161           :ref:`cropping and composing rectangles <v4l2-selections-common>`.
 162
 163     -  .. row 3
 164
 165        -  __u32
 166
 167        -  ``flags``
 168
 169        -  Flags controlling the selection rectangle adjustments, refer to
 170           :ref:`selection flags <v4l2-selection-flags>`.
 171
 172     -  .. row 4
 173
 174        -  struct :ref:`v4l2_rect <v4l2-rect>`
 175
 176        -  ``r``
 177
 178        -  The selection rectangle.
 179
 180     -  .. row 5
 181
 182        -  __u32
 183
 184        -  ``reserved[9]``
 185
 186        -  Reserved fields for future use. Drivers and applications must zero
 187           this array.
 188
 189
 190
 191 Return Value
 192 ============
 193
 194 On success 0 is returned, on error -1 and the ``errno`` variable is set
 195 appropriately. The generic error codes are described at the
 196 :ref:`Generic Error Codes <gen-errors>` chapter.
 197
 198 EINVAL
 199     Given buffer type ``type`` or the selection target ``target`` is not
 200     supported, or the ``flags`` argument is not valid.
 201
 202 ERANGE
 203     It is not possible to adjust struct :ref:`v4l2_rect <v4l2-rect>`
 204     ``r`` rectangle to satisfy all constraints given in the ``flags``
 205     argument.
 206
 207 EBUSY
 208     It is not possible to apply change of the selection rectangle at the
 209     moment. Usually because streaming is in progress.