vidioc-g-crop.rst

  1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
  2.. c:namespace:: V4L
  3
  4.. _VIDIOC_G_CROP:
  5
  6**********************************
  7ioctl VIDIOC_G_CROP, VIDIOC_S_CROP
  8**********************************
  9
 10Name
 11====
 12
 13VIDIOC_G_CROP - VIDIOC_S_CROP - Get or set the current cropping rectangle
 14
 15Synopsis
 16========
 17
 18.. c:macro:: VIDIOC_G_CROP
 19
 20``int ioctl(int fd, VIDIOC_G_CROP, struct v4l2_crop *argp)``
 21
 22.. c:macro:: VIDIOC_S_CROP
 23
 24``int ioctl(int fd, VIDIOC_S_CROP, const struct v4l2_crop *argp)``
 25
 26Arguments
 27=========
 28
 29``fd``
 30    File descriptor returned by :c:func:`open()`.
 31
 32``argp``
 33    Pointer to struct :c:type:`v4l2_crop`.
 34
 35Description
 36===========
 37
 38To query the cropping rectangle size and position applications set the
 39``type`` field of a struct :c:type:`v4l2_crop` structure to the
 40respective buffer (stream) type and call the :ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>` ioctl
 41with a pointer to this structure. The driver fills the rest of the
 42structure or returns the ``EINVAL`` error code if cropping is not supported.
 43
 44To change the cropping rectangle applications initialize the ``type``
 45and struct :c:type:`v4l2_rect` substructure named ``c`` of a
 46v4l2_crop structure and call the :ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` ioctl with a pointer
 47to this structure.
 48
 49The driver first adjusts the requested dimensions against hardware
 50limits, i. e. the bounds given by the capture/output window, and it
 51rounds to the closest possible values of horizontal and vertical offset,
 52width and height. In particular the driver must round the vertical
 53offset of the cropping rectangle to frame lines modulo two, such that
 54the field order cannot be confused.
 55
 56Second the driver adjusts the image size (the opposite rectangle of the
 57scaling process, source or target depending on the data direction) to
 58the closest size possible while maintaining the current horizontal and
 59vertical scaling factor.
 60
 61Finally the driver programs the hardware with the actual cropping and
 62image parameters. :ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` is a write-only ioctl, it does not
 63return the actual parameters. To query them applications must call
 64:ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>` and :ref:`VIDIOC_G_FMT`. When the
 65parameters are unsuitable the application may modify the cropping or
 66image parameters and repeat the cycle until satisfactory parameters have
 67been negotiated.
 68
 69When cropping is not supported then no parameters are changed and
 70:ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` returns the ``EINVAL`` error code.
 71
 72.. c:type:: v4l2_crop
 73
 74.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
 75
 76.. flat-table:: struct v4l2_crop
 77    :header-rows:  0
 78    :stub-columns: 0
 79    :widths:       1 1 2
 80
 81    * - __u32
 82      - ``type``
 83      - Type of the data stream, set by the application. Only these types
 84	are valid here: ``V4L2_BUF_TYPE_VIDEO_CAPTURE``, ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``,
 85	``V4L2_BUF_TYPE_VIDEO_OUTPUT``, ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE`` and
 86	``V4L2_BUF_TYPE_VIDEO_OVERLAY``. See :c:type:`v4l2_buf_type` and the note below.
 87    * - struct :c:type:`v4l2_rect`
 88      - ``c``
 89      - Cropping rectangle. The same co-ordinate system as for struct
 90	:c:type:`v4l2_cropcap` ``bounds`` is used.
 91
 92.. note::
 93   Unfortunately in the case of multiplanar buffer types
 94   (``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``)
 95   this API was messed up with regards to how the :c:type:`v4l2_crop` ``type`` field
 96   should be filled in. Some drivers only accepted the ``_MPLANE`` buffer type while
 97   other drivers only accepted a non-multiplanar buffer type (i.e. without the
 98   ``_MPLANE`` at the end).
 99
100   Starting with kernel 4.13 both variations are allowed.
101
102Return Value
103============
104
105On success 0 is returned, on error -1 and the ``errno`` variable is set
106appropriately. The generic error codes are described at the
107:ref:`Generic Error Codes <gen-errors>` chapter.
108
109ENODATA
110    Cropping is not supported for this input or output.