1.. Permission is granted to copy, distribute and/or modify this
2.. document under the terms of the GNU Free Documentation License,
3.. Version 1.1 or any later version published by the Free Software
4.. Foundation, with no Invariant Sections, no Front-Cover Texts
5.. and no Back-Cover Texts. A copy of the license is included at
6.. Documentation/media/uapi/fdl-appendix.rst.
7..
8.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
9
10.. _VIDIOC_G_SELECTION:
11
12********************************************
13ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION
14********************************************
15
16Name
17====
18
19VIDIOC_G_SELECTION - VIDIOC_S_SELECTION - Get or set one of the selection rectangles
20
21
22Synopsis
23========
24
25.. c:function:: int ioctl( int fd, VIDIOC_G_SELECTION, struct v4l2_selection *argp )
26    :name: VIDIOC_G_SELECTION
27
28
29.. c:function:: int ioctl( int fd, VIDIOC_S_SELECTION, struct v4l2_selection *argp )
30    :name: VIDIOC_S_SELECTION
31
32
33Arguments
34=========
35
36``fd``
37    File descriptor returned by :ref:`open() <func-open>`.
38
39``argp``
40    Pointer to struct :c:type:`v4l2_selection`.
41
42Description
43===========
44
45The ioctls are used to query and configure selection rectangles.
46
47To query the cropping (composing) rectangle set struct
48:c:type:`v4l2_selection` ``type`` field to the
49respective buffer type. The next step is setting the
50value of struct :c:type:`v4l2_selection` ``target``
51field to ``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer
52to table :ref:`v4l2-selections-common` or :ref:`selection-api` for
53additional targets. The ``flags`` and ``reserved`` fields of struct
54:c:type:`v4l2_selection` are ignored and they must be
55filled with zeros. The driver fills the rest of the structure or returns
56EINVAL error code if incorrect buffer type or target was used. If
57cropping (composing) is not supported then the active rectangle is not
58mutable and it is always equal to the bounds rectangle. Finally, the
59struct :c:type:`v4l2_rect` ``r`` rectangle is filled with
60the current cropping (composing) coordinates. The coordinates are
61expressed in driver-dependent units. The only exception are rectangles
62for images in raw formats, whose coordinates are always expressed in
63pixels.
64
65To change the cropping (composing) rectangle set the struct
66:c:type:`v4l2_selection` ``type`` field to the
67respective buffer type. The next step is setting the
68value of struct :c:type:`v4l2_selection` ``target`` to
69``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer to table
70:ref:`v4l2-selections-common` or :ref:`selection-api` for additional
71targets. The struct :c:type:`v4l2_rect` ``r`` rectangle need
72to be set to the desired active area. Field struct
73:c:type:`v4l2_selection` ``reserved`` is ignored and
74must be filled with zeros. The driver may adjust coordinates of the
75requested rectangle. An application may introduce constraints to control
76rounding behaviour. The struct :c:type:`v4l2_selection`
77``flags`` field must be set to one of the following:
78
79-  ``0`` - The driver can adjust the rectangle size freely and shall
80   choose a crop/compose rectangle as close as possible to the requested
81   one.
82
83-  ``V4L2_SEL_FLAG_GE`` - The driver is not allowed to shrink the
84   rectangle. The original rectangle must lay inside the adjusted one.
85
86-  ``V4L2_SEL_FLAG_LE`` - The driver is not allowed to enlarge the
87   rectangle. The adjusted rectangle must lay inside the original one.
88
89-  ``V4L2_SEL_FLAG_GE | V4L2_SEL_FLAG_LE`` - The driver must choose the
90   size exactly the same as in the requested rectangle.
91
92Please refer to :ref:`sel-const-adjust`.
93
94The driver may have to adjusts the requested dimensions against hardware
95limits and other parts as the pipeline, i.e. the bounds given by the
96capture/output window or TV display. The closest possible values of
97horizontal and vertical offset and sizes are chosen according to
98following priority:
99
1001. Satisfy constraints from struct
101   :c:type:`v4l2_selection` ``flags``.
102
1032. Adjust width, height, left, and top to hardware limits and
104   alignments.
105
1063. Keep center of adjusted rectangle as close as possible to the
107   original one.
108
1094. Keep width and height as close as possible to original ones.
110
1115. Keep horizontal and vertical offset as close as possible to original
112   ones.
113
114On success the struct :c:type:`v4l2_rect` ``r`` field
115contains the adjusted rectangle. When the parameters are unsuitable the
116application may modify the cropping (composing) or image parameters and
117repeat the cycle until satisfactory parameters have been negotiated. If
118constraints flags have to be violated at then ``ERANGE`` is returned. The
119error indicates that *there exist no rectangle* that satisfies the
120constraints.
121
122Selection targets and flags are documented in
123:ref:`v4l2-selections-common`.
124
125
126.. _sel-const-adjust:
127
128.. kernel-figure::  constraints.svg
129    :alt:    constraints.svg
130    :align:  center
131
132    Size adjustments with constraint flags.
133
134    Behaviour of rectangle adjustment for different constraint flags.
135
136
137
138
139.. c:type:: v4l2_selection
140
141.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
142
143.. flat-table:: struct v4l2_selection
144    :header-rows:  0
145    :stub-columns: 0
146    :widths:       1 1 2
147
148    * - __u32
149      - ``type``
150      - Type of the buffer (from enum
151	:c:type:`v4l2_buf_type`).
152    * - __u32
153      - ``target``
154      - Used to select between
155	:ref:`cropping and composing rectangles <v4l2-selections-common>`.
156    * - __u32
157      - ``flags``
158      - Flags controlling the selection rectangle adjustments, refer to
159	:ref:`selection flags <v4l2-selection-flags>`.
160    * - struct :c:type:`v4l2_rect`
161      - ``r``
162      - The selection rectangle.
163    * - __u32
164      - ``reserved[9]``
165      - Reserved fields for future use. Drivers and applications must zero
166	this array.
167
168.. note::
169   Unfortunately in the case of multiplanar buffer types
170   (``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``)
171   this API was messed up with regards to how the :c:type:`v4l2_selection` ``type`` field
172   should be filled in. Some drivers only accepted the ``_MPLANE`` buffer type while
173   other drivers only accepted a non-multiplanar buffer type (i.e. without the
174   ``_MPLANE`` at the end).
175
176   Starting with kernel 4.13 both variations are allowed.
177
178
179Return Value
180============
181
182On success 0 is returned, on error -1 and the ``errno`` variable is set
183appropriately. The generic error codes are described at the
184:ref:`Generic Error Codes <gen-errors>` chapter.
185
186EINVAL
187    Given buffer type ``type`` or the selection target ``target`` is not
188    supported, or the ``flags`` argument is not valid.
189
190ERANGE
191    It is not possible to adjust struct :c:type:`v4l2_rect`
192    ``r`` rectangle to satisfy all constraints given in the ``flags``
193    argument.
194
195ENODATA
196    Selection is not supported for this input or output.
197
198EBUSY
199    It is not possible to apply change of the selection rectangle at the
200    moment. Usually because streaming is in progress.
201