Commit | Line | Data |
---|---|---|
5377d91f MH |
1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_G_SELECTION: |
5377d91f MH |
4 | |
5 | ******************************************** | |
6 | ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION | |
7 | ******************************************** | |
8 | ||
15e7d615 | 9 | Name |
586027ce | 10 | ==== |
5377d91f | 11 | |
586027ce | 12 | VIDIOC_G_SELECTION - VIDIOC_S_SELECTION - Get or set one of the selection rectangles |
5377d91f | 13 | |
15e7d615 MCC |
14 | |
15 | Synopsis | |
5377d91f MH |
16 | ======== |
17 | ||
b7e67f6c | 18 | .. cpp:function:: int ioctl( int fd, int request, struct v4l2_selection *argp ) |
5377d91f | 19 | |
586027ce | 20 | |
15e7d615 | 21 | Arguments |
5377d91f MH |
22 | ========= |
23 | ||
24 | ``fd`` | |
25 | File descriptor returned by :ref:`open() <func-open>`. | |
26 | ||
27 | ``request`` | |
28 | VIDIOC_G_SELECTION, VIDIOC_S_SELECTION | |
29 | ||
30 | ``argp`` | |
31 | ||
32 | ||
15e7d615 | 33 | Description |
5377d91f MH |
34 | =========== |
35 | ||
36 | The ioctls are used to query and configure selection rectangles. | |
37 | ||
38 | To query the cropping (composing) rectangle set struct | |
39 | :ref:`v4l2_selection <v4l2-selection>` ``type`` field to the | |
40 | respective buffer type. Do not use the multiplanar buffer types. Use | |
41 | ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` instead of | |
42 | ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and use | |
43 | ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` instead of | |
44 | ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``. The next step is setting the | |
45 | value of struct :ref:`v4l2_selection <v4l2-selection>` ``target`` | |
46 | field to ``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer | |
47 | to table :ref:`v4l2-selections-common` or :ref:`selection-api` for | |
48 | additional targets. The ``flags`` and ``reserved`` fields of struct | |
49 | :ref:`v4l2_selection <v4l2-selection>` are ignored and they must be | |
50 | filled with zeros. The driver fills the rest of the structure or returns | |
51 | EINVAL error code if incorrect buffer type or target was used. If | |
52 | cropping (composing) is not supported then the active rectangle is not | |
53 | mutable and it is always equal to the bounds rectangle. Finally, the | |
54 | struct :ref:`v4l2_rect <v4l2-rect>` ``r`` rectangle is filled with | |
55 | the current cropping (composing) coordinates. The coordinates are | |
56 | expressed in driver-dependent units. The only exception are rectangles | |
57 | for images in raw formats, whose coordinates are always expressed in | |
58 | pixels. | |
59 | ||
60 | To change the cropping (composing) rectangle set the struct | |
61 | :ref:`v4l2_selection <v4l2-selection>` ``type`` field to the | |
62 | respective buffer type. Do not use multiplanar buffers. Use | |
63 | ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` instead of | |
64 | ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. Use | |
65 | ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` instead of | |
66 | ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``. The next step is setting the | |
67 | value of struct :ref:`v4l2_selection <v4l2-selection>` ``target`` to | |
68 | ``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer to table | |
69 | :ref:`v4l2-selections-common` or :ref:`selection-api` for additional | |
70 | targets. The struct :ref:`v4l2_rect <v4l2-rect>` ``r`` rectangle need | |
71 | to be set to the desired active area. Field struct | |
72 | :ref:`v4l2_selection <v4l2-selection>` ``reserved`` is ignored and | |
73 | must be filled with zeros. The driver may adjust coordinates of the | |
74 | requested rectangle. An application may introduce constraints to control | |
75 | rounding behaviour. The struct :ref:`v4l2_selection <v4l2-selection>` | |
76 | ``flags`` field must be set to one of the following: | |
77 | ||
78 | - ``0`` - The driver can adjust the rectangle size freely and shall | |
79 | choose a crop/compose rectangle as close as possible to the requested | |
80 | one. | |
81 | ||
82 | - ``V4L2_SEL_FLAG_GE`` - The driver is not allowed to shrink the | |
83 | rectangle. The original rectangle must lay inside the adjusted one. | |
84 | ||
85 | - ``V4L2_SEL_FLAG_LE`` - The driver is not allowed to enlarge the | |
86 | rectangle. The adjusted rectangle must lay inside the original one. | |
87 | ||
88 | - ``V4L2_SEL_FLAG_GE | V4L2_SEL_FLAG_LE`` - The driver must choose the | |
89 | size exactly the same as in the requested rectangle. | |
90 | ||
91 | Please refer to :ref:`sel-const-adjust`. | |
92 | ||
93 | The driver may have to adjusts the requested dimensions against hardware | |
94 | limits and other parts as the pipeline, i.e. the bounds given by the | |
95 | capture/output window or TV display. The closest possible values of | |
96 | horizontal and vertical offset and sizes are chosen according to | |
97 | following priority: | |
98 | ||
99 | 1. Satisfy constraints from struct | |
100 | :ref:`v4l2_selection <v4l2-selection>` ``flags``. | |
101 | ||
102 | 2. Adjust width, height, left, and top to hardware limits and | |
103 | alignments. | |
104 | ||
105 | 3. Keep center of adjusted rectangle as close as possible to the | |
106 | original one. | |
107 | ||
108 | 4. Keep width and height as close as possible to original ones. | |
109 | ||
110 | 5. Keep horizontal and vertical offset as close as possible to original | |
111 | ones. | |
112 | ||
113 | On success the struct :ref:`v4l2_rect <v4l2-rect>` ``r`` field | |
114 | contains the adjusted rectangle. When the parameters are unsuitable the | |
115 | application may modify the cropping (composing) or image parameters and | |
116 | repeat the cycle until satisfactory parameters have been negotiated. If | |
cdb4af0f | 117 | constraints flags have to be violated at then ``ERANGE`` is returned. The |
5377d91f MH |
118 | error indicates that *there exist no rectangle* that satisfies the |
119 | constraints. | |
120 | ||
121 | Selection targets and flags are documented in | |
122 | :ref:`v4l2-selections-common`. | |
123 | ||
124 | ||
125 | .. _sel-const-adjust: | |
126 | ||
127 | .. figure:: vidioc-g-selection_files/constraints.* | |
128 | :alt: constraints.png | |
129 | :align: center | |
130 | ||
131 | Size adjustments with constraint flags. | |
132 | ||
133 | Behaviour of rectangle adjustment for different constraint flags. | |
134 | ||
135 | ||
136 | ||
137 | ||
138 | .. _v4l2-selection: | |
139 | ||
140 | .. flat-table:: struct v4l2_selection | |
141 | :header-rows: 0 | |
142 | :stub-columns: 0 | |
143 | :widths: 1 1 2 | |
144 | ||
145 | ||
146 | - .. row 1 | |
147 | ||
148 | - __u32 | |
149 | ||
150 | - ``type`` | |
151 | ||
152 | - Type of the buffer (from enum | |
0579e6e3 | 153 | :ref:`v4l2_buf_type <v4l2-buf-type>`). |
5377d91f MH |
154 | |
155 | - .. row 2 | |
156 | ||
157 | - __u32 | |
158 | ||
159 | - ``target`` | |
160 | ||
161 | - Used to select between | |
0579e6e3 | 162 | :ref:`cropping and composing rectangles <v4l2-selections-common>`. |
5377d91f MH |
163 | |
164 | - .. row 3 | |
165 | ||
166 | - __u32 | |
167 | ||
168 | - ``flags`` | |
169 | ||
170 | - Flags controlling the selection rectangle adjustments, refer to | |
0579e6e3 | 171 | :ref:`selection flags <v4l2-selection-flags>`. |
5377d91f MH |
172 | |
173 | - .. row 4 | |
174 | ||
175 | - struct :ref:`v4l2_rect <v4l2-rect>` | |
176 | ||
177 | - ``r`` | |
178 | ||
179 | - The selection rectangle. | |
180 | ||
181 | - .. row 5 | |
182 | ||
183 | - __u32 | |
184 | ||
8968da9b | 185 | - ``reserved[9]`` |
5377d91f MH |
186 | |
187 | - Reserved fields for future use. Drivers and applications must zero | |
0579e6e3 | 188 | this array. |
5377d91f MH |
189 | |
190 | ||
15e7d615 | 191 | Return Value |
5377d91f MH |
192 | ============ |
193 | ||
194 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
195 | appropriately. The generic error codes are described at the | |
196 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
197 | ||
198 | EINVAL | |
199 | Given buffer type ``type`` or the selection target ``target`` is not | |
200 | supported, or the ``flags`` argument is not valid. | |
201 | ||
202 | ERANGE | |
203 | It is not possible to adjust struct :ref:`v4l2_rect <v4l2-rect>` | |
204 | ``r`` rectangle to satisfy all constraints given in the ``flags`` | |
205 | argument. | |
206 | ||
207 | EBUSY | |
208 | It is not possible to apply change of the selection rectangle at the | |
209 | moment. Usually because streaming is in progress. |