1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L
3
4 .. _VIDIOC_G_CROP:
5
6 **********************************
7 ioctl VIDIOC_G_CROP, VIDIOC_S_CROP
8 **********************************
9
10 Name
11 ====
12
13 VIDIOC_G_CROP - VIDIOC_S_CROP - Get or set the current cropping rectangle
14
15 Synopsis
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
26 Arguments
27 =========
28
29 ``fd``
30 File descriptor returned by :c:func:`open()`.
31
32 ``argp``
33 Pointer to struct :c:type:`v4l2_crop`.
34
35 Description
36 ===========
37
38 To query the cropping rectangle size and position applications set the
39 ``type`` field of a struct :c:type:`v4l2_crop` structure to the
40 respective buffer (stream) type and call the :ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>` ioctl
41 with a pointer to this structure. The driver fills the rest of the
42 structure or returns the ``EINVAL`` error code if cropping is not supported.
43
44 To change the cropping rectangle applications initialize the ``type``
45 and struct :c:type:`v4l2_rect` substructure named ``c`` of a
46 v4l2_crop structure and call the :ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` ioctl with a pointer
47 to this structure.
48
49 The driver first adjusts the requested dimensions against hardware
50 limits, i. e. the bounds given by the capture/output window, and it
51 rounds to the closest possible values of horizontal and vertical offset,
52 width and height. In particular the driver must round the vertical
53 offset of the cropping rectangle to frame lines modulo two, such that
54 the field order cannot be confused.
55
56 Second the driver adjusts the image size (the opposite rectangle of the
57 scaling process, source or target depending on the data direction) to
58 the closest size possible while maintaining the current horizontal and
59 vertical scaling factor.
60
61 Finally the driver programs the hardware with the actual cropping and
62 image parameters. :ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` is a write-only ioctl, it does not
63 return the actual parameters. To query them applications must call
64 :ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>` and :ref:`VIDIOC_G_FMT`. When the
65 parameters are unsuitable the application may modify the cropping or
66 image parameters and repeat the cycle until satisfactory parameters have
67 been negotiated.
68
69 When 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
102 Return Value
103 ============
104
105 On success 0 is returned, on error -1 and the ``errno`` variable is set
106 appropriately. The generic error codes are described at the
107 :ref:`Generic Error Codes <gen-errors>` chapter.
108
109 ENODATA
110 Cropping is not supported for this input or output.
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