1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L
3
4 .. _VIDIOC_CROPCAP:
5
6 ********************
7 ioctl VIDIOC_CROPCAP
8 ********************
9
10 Name
11 ====
12
13 VIDIOC_CROPCAP - Information about the video cropping and scaling abilities
14
15 Synopsis
16 ========
17
18 .. c:macro:: VIDIOC_CROPCAP
19
20 ``int ioctl(int fd, VIDIOC_CROPCAP, struct v4l2_cropcap *argp)``
21
22 Arguments
23 =========
24
25 ``fd``
26 File descriptor returned by :c:func:`open()`.
27
28 ``argp``
29 Pointer to struct :c:type:`v4l2_cropcap`.
30
31 Description
32 ===========
33
34 Applications use this function to query the cropping limits, the pixel
35 aspect of images and to calculate scale factors. They set the ``type``
36 field of a v4l2_cropcap structure to the respective buffer (stream)
37 type and call the :ref:`VIDIOC_CROPCAP` ioctl with a pointer to this
38 structure. Drivers fill the rest of the structure. The results are
39 constant except when switching the video standard. Remember this switch
40 can occur implicit when switching the video input or output.
41
42 This ioctl must be implemented for video capture or output devices that
43 support cropping and/or scaling and/or have non-square pixels, and for
44 overlay 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
121 Return Value
122 ============
123
124 On success 0 is returned, on error -1 and the ``errno`` variable is set
125 appropriately. The generic error codes are described at the
126 :ref:`Generic Error Codes <gen-errors>` chapter.
127
128 EINVAL
129 The struct :c:type:`v4l2_cropcap` ``type`` is
130 invalid.
131
132 ENODATA
133 Cropping is not supported for this input or output.
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