vidioc-cropcap.rst

  1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
  2.. c:namespace:: V4L
  3
  4.. _VIDIOC_CROPCAP:
  5
  6********************
  7ioctl VIDIOC_CROPCAP
  8********************
  9
 10Name
 11====
 12
 13VIDIOC_CROPCAP - Information about the video cropping and scaling abilities
 14
 15Synopsis
 16========
 17
 18.. c:macro:: VIDIOC_CROPCAP
 19
 20``int ioctl(int fd, VIDIOC_CROPCAP, struct v4l2_cropcap *argp)``
 21
 22Arguments
 23=========
 24
 25``fd``
 26    File descriptor returned by :c:func:`open()`.
 27
 28``argp``
 29    Pointer to struct :c:type:`v4l2_cropcap`.
 30
 31Description
 32===========
 33
 34Applications use this function to query the cropping limits, the pixel
 35aspect of images and to calculate scale factors. They set the ``type``
 36field of a v4l2_cropcap structure to the respective buffer (stream)
 37type and call the :ref:`VIDIOC_CROPCAP` ioctl with a pointer to this
 38structure. Drivers fill the rest of the structure. The results are
 39constant except when switching the video standard. Remember this switch
 40can occur implicit when switching the video input or output.
 41
 42This ioctl must be implemented for video capture or output devices that
 43support cropping and/or scaling and/or have non-square pixels, and for
 44overlay devices.
 45
 46.. c:type:: v4l2_cropcap
 47
 48.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
 49
 50.. flat-table:: struct v4l2_cropcap
 51    :header-rows:  0
 52    :stub-columns: 0
 53    :widths:       1 1 2
 54
 55    * - __u32
 56      - ``type``
 57      - Type of the data stream, set by the application. Only these types
 58	are valid here: ``V4L2_BUF_TYPE_VIDEO_CAPTURE``, ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``,
 59	``V4L2_BUF_TYPE_VIDEO_OUTPUT``, ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE`` and
 60	``V4L2_BUF_TYPE_VIDEO_OVERLAY``. See :c:type:`v4l2_buf_type` and the note below.
 61    * - struct :ref:`v4l2_rect <v4l2-rect-crop>`
 62      - ``bounds``
 63      - Defines the window within capturing or output is possible, this
 64	may exclude for example the horizontal and vertical blanking
 65	areas. The cropping rectangle cannot exceed these limits. Width
 66	and height are defined in pixels, the driver writer is free to
 67	choose origin and units of the coordinate system in the analog
 68	domain.
 69    * - struct :ref:`v4l2_rect <v4l2-rect-crop>`
 70      - ``defrect``
 71      - Default cropping rectangle, it shall cover the "whole picture".
 72	Assuming pixel aspect 1/1 this could be for example a 640 × 480
 73	rectangle for NTSC, a 768 × 576 rectangle for PAL and SECAM
 74	centered over the active picture area. The same coordinate system
 75	as for ``bounds`` is used.
 76    * - struct :c:type:`v4l2_fract`
 77      - ``pixelaspect``
 78      - This is the pixel aspect (y / x) when no scaling is applied, the
 79	ratio of the actual sampling frequency and the frequency required
 80	to get square pixels.
 81
 82	When cropping coordinates refer to square pixels, the driver sets
 83	``pixelaspect`` to 1/1. Other common values are 54/59 for PAL and
 84	SECAM, 11/10 for NTSC sampled according to [:ref:`itu601`].
 85
 86.. note::
 87   Unfortunately in the case of multiplanar buffer types
 88   (``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``)
 89   this API was messed up with regards to how the :c:type:`v4l2_cropcap` ``type`` field
 90   should be filled in. Some drivers only accepted the ``_MPLANE`` buffer type while
 91   other drivers only accepted a non-multiplanar buffer type (i.e. without the
 92   ``_MPLANE`` at the end).
 93
 94   Starting with kernel 4.13 both variations are allowed.
 95
 96
 97.. _v4l2-rect-crop:
 98
 99.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
100
101.. flat-table:: struct v4l2_rect
102    :header-rows:  0
103    :stub-columns: 0
104    :widths:       1 1 2
105
106    * - __s32
107      - ``left``
108      - Horizontal offset of the top, left corner of the rectangle, in
109	pixels.
110    * - __s32
111      - ``top``
112      - Vertical offset of the top, left corner of the rectangle, in
113	pixels.
114    * - __u32
115      - ``width``
116      - Width of the rectangle, in pixels.
117    * - __u32
118      - ``height``
119      - Height of the rectangle, in pixels.
120
121Return Value
122============
123
124On success 0 is returned, on error -1 and the ``errno`` variable is set
125appropriately. The generic error codes are described at the
126:ref:`Generic Error Codes <gen-errors>` chapter.
127
128EINVAL
129    The struct :c:type:`v4l2_cropcap` ``type`` is
130    invalid.
131
132ENODATA
133    Cropping is not supported for this input or output.