1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: V4L
3
4.. _VIDIOC_G_SELECTION:
5
6********************************************
7ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION
8********************************************
9
10Name
11====
12
13VIDIOC_G_SELECTION - VIDIOC_S_SELECTION - Get or set one of the selection rectangles
14
15Synopsis
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
26Arguments
27=========
28
29``fd``
30    File descriptor returned by :c:func:`open()`.
31
32``argp``
33    Pointer to struct :c:type:`v4l2_selection`.
34
35Description
36===========
37
38The ioctls are used to query and configure selection rectangles.
39
40To query the cropping (composing) rectangle set struct
41:c:type:`v4l2_selection` ``type`` field to the
42respective buffer type. The next step is setting the
43value of struct :c:type:`v4l2_selection` ``target``
44field to ``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer
45to table :ref:`v4l2-selections-common` or :ref:`selection-api` for
46additional targets. The ``flags`` and ``reserved`` fields of struct
47:c:type:`v4l2_selection` are ignored and they must be
48filled with zeros. The driver fills the rest of the structure or returns
49EINVAL error code if incorrect buffer type or target was used. If
50cropping (composing) is not supported then the active rectangle is not
51mutable and it is always equal to the bounds rectangle. Finally, the
52struct :c:type:`v4l2_rect` ``r`` rectangle is filled with
53the current cropping (composing) coordinates. The coordinates are
54expressed in driver-dependent units. The only exception are rectangles
55for images in raw formats, whose coordinates are always expressed in
56pixels.
57
58To change the cropping (composing) rectangle set the struct
59:c:type:`v4l2_selection` ``type`` field to the
60respective buffer type. The next step is setting the
61value 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
64targets. The struct :c:type:`v4l2_rect` ``r`` rectangle need
65to be set to the desired active area. Field struct
66:c:type:`v4l2_selection` ``reserved`` is ignored and
67must be filled with zeros. The driver may adjust coordinates of the
68requested rectangle. An application may introduce constraints to control
69rounding 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
85Please refer to :ref:`sel-const-adjust`.
86
87The driver may have to adjusts the requested dimensions against hardware
88limits and other parts as the pipeline, i.e. the bounds given by the
89capture/output window or TV display. The closest possible values of
90horizontal and vertical offset and sizes are chosen according to
91following priority:
92
931. Satisfy constraints from struct
94   :c:type:`v4l2_selection` ``flags``.
95
962. Adjust width, height, left, and top to hardware limits and
97   alignments.
98
993. Keep center of adjusted rectangle as close as possible to the
100   original one.
101
1024. Keep width and height as close as possible to original ones.
103
1045. Keep horizontal and vertical offset as close as possible to original
105   ones.
106
107On success the struct :c:type:`v4l2_rect` ``r`` field
108contains the adjusted rectangle. When the parameters are unsuitable the
109application may modify the cropping (composing) or image parameters and
110repeat the cycle until satisfactory parameters have been negotiated. If
111constraints flags have to be violated at then ``ERANGE`` is returned. The
112error indicates that *there exist no rectangle* that satisfies the
113constraints.
114
115Selection 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
169Return Value
170============
171
172On success 0 is returned, on error -1 and the ``errno`` variable is set
173appropriately. The generic error codes are described at the
174:ref:`Generic Error Codes <gen-errors>` chapter.
175
176EINVAL
177    Given buffer type ``type`` or the selection target ``target`` is not
178    supported, or the ``flags`` argument is not valid.
179
180ERANGE
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
185ENODATA
186    Selection is not supported for this input or output.
187
188EBUSY
189    It is not possible to apply change of the selection rectangle at the
190    moment. Usually because streaming is in progress.
191