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

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _VIDIOC_G_CROP:
   4
   5 **********************************
   6 ioctl VIDIOC_G_CROP, VIDIOC_S_CROP
   7 **********************************
   8
   9 *man VIDIOC_G_CROP(2)*
  10
  11 VIDIOC_S_CROP
  12 Get or set the current cropping rectangle
  13
  14
  15 Synopsis
  16 ========
  17
  18 .. c:function:: int ioctl( int fd, int request, struct v4l2_crop *argp )
  19
  20 .. c:function:: int ioctl( int fd, int request, const struct v4l2_crop *argp )
  21
  22 Arguments
  23 =========
  24
  25 ``fd``
  26     File descriptor returned by :ref:`open() <func-open>`.
  27
  28 ``request``
  29     VIDIOC_G_CROP, VIDIOC_S_CROP
  30
  31 ``argp``
  32
  33
  34 Description
  35 ===========
  36
  37 To query the cropping rectangle size and position applications set the
  38 ``type`` field of a :c:type:`struct v4l2_crop` structure to the
  39 respective buffer (stream) type and call the :ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>` ioctl
  40 with a pointer to this structure. The driver fills the rest of the
  41 structure or returns the EINVAL error code if cropping is not supported.
  42
  43 To change the cropping rectangle applications initialize the ``type``
  44 and struct :ref:`v4l2_rect <v4l2-rect>` substructure named ``c`` of a
  45 v4l2_crop structure and call the :ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` ioctl with a pointer
  46 to this structure.
  47
  48 Do not use the multiplanar buffer types. Use
  49 ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` instead of
  50 ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and use
  51 ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` instead of
  52 ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``.
  53
  54 The driver first adjusts the requested dimensions against hardware
  55 limits, i. e. the bounds given by the capture/output window, and it
  56 rounds to the closest possible values of horizontal and vertical offset,
  57 width and height. In particular the driver must round the vertical
  58 offset of the cropping rectangle to frame lines modulo two, such that
  59 the field order cannot be confused.
  60
  61 Second the driver adjusts the image size (the opposite rectangle of the
  62 scaling process, source or target depending on the data direction) to
  63 the closest size possible while maintaining the current horizontal and
  64 vertical scaling factor.
  65
  66 Finally the driver programs the hardware with the actual cropping and
  67 image parameters. :ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` is a write-only ioctl, it does not
  68 return the actual parameters. To query them applications must call
  69 :ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>` and :ref:`VIDIOC_G_FMT`. When the
  70 parameters are unsuitable the application may modify the cropping or
  71 image parameters and repeat the cycle until satisfactory parameters have
  72 been negotiated.
  73
  74 When cropping is not supported then no parameters are changed and
  75 :ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` returns the EINVAL error code.
  76
  77
  78 .. _v4l2-crop:
  79
  80 .. flat-table:: struct v4l2_crop
  81     :header-rows:  0
  82     :stub-columns: 0
  83     :widths:       1 1 2
  84
  85
  86     -  .. row 1
  87
  88        -  __u32
  89
  90        -  ``type``
  91
  92        -  Type of the data stream, set by the application. Only these types
  93           are valid here: ``V4L2_BUF_TYPE_VIDEO_CAPTURE``,
  94           ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` and
  95           ``V4L2_BUF_TYPE_VIDEO_OVERLAY``. See :ref:`v4l2-buf-type`.
  96
  97     -  .. row 2
  98
  99        -  struct :ref:`v4l2_rect <v4l2-rect>`
 100
 101        -  ``c``
 102
 103        -  Cropping rectangle. The same co-ordinate system as for struct
 104           :ref:`v4l2_cropcap <v4l2-cropcap>` ``bounds`` is used.
 105
 106
 107
 108 Return Value
 109 ============
 110
 111 On success 0 is returned, on error -1 and the ``errno`` variable is set
 112 appropriately. The generic error codes are described at the
 113 :ref:`Generic Error Codes <gen-errors>` chapter.
 114
 115
 116 .. ------------------------------------------------------------------------------
 117 .. This file was automatically converted from DocBook-XML with the dbxml
 118 .. library (https://github.com/return42/sphkerneldoc). The origin XML comes
 119 .. from the linux kernel, refer to:
 120 ..
 121 .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
 122 .. ------------------------------------------------------------------------------