1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2
3.. _VIDIOC_G_SELECTION:
4
5********************************************
6ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION
7********************************************
8
9Name
10====
11
12VIDIOC_G_SELECTION - VIDIOC_S_SELECTION - Get or set one of the selection rectangles
13
14
15Synopsis
16========
17
18.. c:function:: int ioctl( int fd, VIDIOC_G_SELECTION, struct v4l2_selection *argp )
19    :name: VIDIOC_G_SELECTION
20
21
22.. c:function:: int ioctl( int fd, VIDIOC_S_SELECTION, struct v4l2_selection *argp )
23    :name: VIDIOC_S_SELECTION
24
25
26Arguments
27=========
28
29``fd``
30    File descriptor returned by :ref:`open() <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
119.. _sel-const-adjust:
120
121.. kernel-figure::  constraints.svg
122    :alt:    constraints.svg
123    :align:  center
124
125    Size adjustments with constraint flags.
126
127    Behaviour of rectangle adjustment for different constraint flags.
128
129
130
131
132.. c:type:: v4l2_selection
133
134.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
135
136.. flat-table:: struct v4l2_selection
137    :header-rows:  0
138    :stub-columns: 0
139    :widths:       1 1 2
140
141    * - __u32
142      - ``type``
143      - Type of the buffer (from enum
144	:c:type:`v4l2_buf_type`).
145    * - __u32
146      - ``target``
147      - Used to select between
148	:ref:`cropping and composing rectangles <v4l2-selections-common>`.
149    * - __u32
150      - ``flags``
151      - Flags controlling the selection rectangle adjustments, refer to
152	:ref:`selection flags <v4l2-selection-flags>`.
153    * - struct :c:type:`v4l2_rect`
154      - ``r``
155      - The selection rectangle.
156    * - __u32
157      - ``reserved[9]``
158      - Reserved fields for future use. Drivers and applications must zero
159	this array.
160
161.. note::
162   Unfortunately in the case of multiplanar buffer types
163   (``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``)
164   this API was messed up with regards to how the :c:type:`v4l2_selection` ``type`` field
165   should be filled in. Some drivers only accepted the ``_MPLANE`` buffer type while
166   other drivers only accepted a non-multiplanar buffer type (i.e. without the
167   ``_MPLANE`` at the end).
168
169   Starting with kernel 4.13 both variations are allowed.
170
171
172Return Value
173============
174
175On success 0 is returned, on error -1 and the ``errno`` variable is set
176appropriately. The generic error codes are described at the
177:ref:`Generic Error Codes <gen-errors>` chapter.
178
179EINVAL
180    Given buffer type ``type`` or the selection target ``target`` is not
181    supported, or the ``flags`` argument is not valid.
182
183ERANGE
184    It is not possible to adjust struct :c:type:`v4l2_rect`
185    ``r`` rectangle to satisfy all constraints given in the ``flags``
186    argument.
187
188ENODATA
189    Selection is not supported for this input or output.
190
191EBUSY
192    It is not possible to apply change of the selection rectangle at the
193    moment. Usually because streaming is in progress.
194