1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 .. c:namespace:: V4L
3
4 .. _VIDIOC_G_SELECTION:
5
6 ********************************************
7 ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION
8 ********************************************
9
10 Name
11 ====
12
13 VIDIOC_G_SELECTION - VIDIOC_S_SELECTION - Get or set one of the selection rectangles
14
15 Synopsis
16 ========
17
18 .. c:macro:: VIDIOC_G_SELECTION
19
20 ``int ioctl(int fd, VIDIOC_G_SELECTION, struct v4l2_selection *argp)``
21
22 .. c:macro:: VIDIOC_S_SELECTION
23
24 ``int ioctl(int fd, VIDIOC_S_SELECTION, struct v4l2_selection *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_selection`.
34
35 Description
36 ===========
37
38 The ioctls are used to query and configure selection rectangles.
39
40 To query the cropping (composing) rectangle set struct
41 :c:type:`v4l2_selection` ``type`` field to the
42 respective buffer type. The next step is setting the
43 value of struct :c:type:`v4l2_selection` ``target``
44 field to ``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer
45 to table :ref:`v4l2-selections-common` or :ref:`selection-api` for
46 additional targets. The ``flags`` and ``reserved`` fields of struct
47 :c:type:`v4l2_selection` are ignored and they must be
48 filled with zeros. The driver fills the rest of the structure or returns
49 EINVAL error code if incorrect buffer type or target was used. If
50 cropping (composing) is not supported then the active rectangle is not
51 mutable and it is always equal to the bounds rectangle. Finally, the
52 struct :c:type:`v4l2_rect` ``r`` rectangle is filled with
53 the current cropping (composing) coordinates. The coordinates are
54 expressed in driver-dependent units. The only exception are rectangles
55 for images in raw formats, whose coordinates are always expressed in
56 pixels.
57
58 To change the cropping (composing) rectangle set the struct
59 :c:type:`v4l2_selection` ``type`` field to the
60 respective buffer type. The next step is setting the
61 value of struct :c:type:`v4l2_selection` ``target`` to
62 ``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer to table
63 :ref:`v4l2-selections-common` or :ref:`selection-api` for additional
64 targets. The struct :c:type:`v4l2_rect` ``r`` rectangle need
65 to be set to the desired active area. Field struct
66 :c:type:`v4l2_selection` ``reserved`` is ignored and
67 must be filled with zeros. The driver may adjust coordinates of the
68 requested rectangle. An application may introduce constraints to control
69 rounding behaviour. The struct :c:type:`v4l2_selection`
70 ``flags`` field must be set to one of the following:
71
72 - ``0`` - The driver can adjust the rectangle size freely and shall
73 choose a crop/compose rectangle as close as possible to the requested
74 one.
75
76 - ``V4L2_SEL_FLAG_GE`` - The driver is not allowed to shrink the
77 rectangle. The original rectangle must lay inside the adjusted one.
78
79 - ``V4L2_SEL_FLAG_LE`` - The driver is not allowed to enlarge the
80 rectangle. The adjusted rectangle must lay inside the original one.
81
82 - ``V4L2_SEL_FLAG_GE | V4L2_SEL_FLAG_LE`` - The driver must choose the
83 size exactly the same as in the requested rectangle.
84
85 Please refer to :ref:`sel-const-adjust`.
86
87 The driver may have to adjusts the requested dimensions against hardware
88 limits and other parts as the pipeline, i.e. the bounds given by the
89 capture/output window or TV display. The closest possible values of
90 horizontal and vertical offset and sizes are chosen according to
91 following priority:
92
93 1. Satisfy constraints from struct
94 :c:type:`v4l2_selection` ``flags``.
95
96 2. Adjust width, height, left, and top to hardware limits and
97 alignments.
98
99 3. Keep center of adjusted rectangle as close as possible to the
100 original one.
101
102 4. Keep width and height as close as possible to original ones.
103
104 5. Keep horizontal and vertical offset as close as possible to original
105 ones.
106
107 On success the struct :c:type:`v4l2_rect` ``r`` field
108 contains the adjusted rectangle. When the parameters are unsuitable the
109 application may modify the cropping (composing) or image parameters and
110 repeat the cycle until satisfactory parameters have been negotiated. If
111 constraints flags have to be violated at then ``ERANGE`` is returned. The
112 error indicates that *there exist no rectangle* that satisfies the
113 constraints.
114
115 Selection targets and flags are documented in
116 :ref:`v4l2-selections-common`.
117
118 .. _sel-const-adjust:
119
120 .. kernel-figure:: constraints.svg
121 :alt: constraints.svg
122 :align: center
123
124 Size adjustments with constraint flags.
125
126 Behaviour of rectangle adjustment for different constraint flags.
127
128
129
130 .. c:type:: v4l2_selection
131
132 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
133
134 .. flat-table:: struct v4l2_selection
135 :header-rows: 0
136 :stub-columns: 0
137 :widths: 1 1 2
138
139 * - __u32
140 - ``type``
141 - Type of the buffer (from enum
142 :c:type:`v4l2_buf_type`).
143 * - __u32
144 - ``target``
145 - Used to select between
146 :ref:`cropping and composing rectangles <v4l2-selections-common>`.
147 * - __u32
148 - ``flags``
149 - Flags controlling the selection rectangle adjustments, refer to
150 :ref:`selection flags <v4l2-selection-flags>`.
151 * - struct :c:type:`v4l2_rect`
152 - ``r``
153 - The selection rectangle.
154 * - __u32
155 - ``reserved[9]``
156 - Reserved fields for future use. Drivers and applications must zero
157 this array.
158
159 .. note::
160 Unfortunately in the case of multiplanar buffer types
161 (``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``)
162 this API was messed up with regards to how the :c:type:`v4l2_selection` ``type`` field
163 should be filled in. Some drivers only accepted the ``_MPLANE`` buffer type while
164 other drivers only accepted a non-multiplanar buffer type (i.e. without the
165 ``_MPLANE`` at the end).
166
167 Starting with kernel 4.13 both variations are allowed.
168
169 Return Value
170 ============
171
172 On success 0 is returned, on error -1 and the ``errno`` variable is set
173 appropriately. The generic error codes are described at the
174 :ref:`Generic Error Codes <gen-errors>` chapter.
175
176 EINVAL
177 Given buffer type ``type`` or the selection target ``target`` is not
178 supported, or the ``flags`` argument is not valid.
179
180 ERANGE
181 It is not possible to adjust struct :c:type:`v4l2_rect`
182 ``r`` rectangle to satisfy all constraints given in the ``flags``
183 argument.
184
185 ENODATA
186 Selection is not supported for this input or output.
187
188 EBUSY
189 It is not possible to apply change of the selection rectangle at the
190 moment. Usually because streaming is in progress.
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