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1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_CROPCAP: |
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4 | |
5 | ******************** | |
6 | ioctl VIDIOC_CROPCAP | |
7 | ******************** | |
8 | ||
15e7d615 | 9 | Name |
586027ce | 10 | ==== |
5377d91f | 11 | |
586027ce | 12 | VIDIOC_CROPCAP - Information about the video cropping and scaling abilities |
5377d91f | 13 | |
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14 | |
15 | Synopsis | |
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16 | ======== |
17 | ||
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18 | .. c:function:: int ioctl( int fd, VIDIOC_CROPCAP, struct v4l2_cropcap *argp ) |
19 | :name: VIDIOC_CROPCAP | |
5377d91f | 20 | |
586027ce | 21 | |
15e7d615 | 22 | Arguments |
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23 | ========= |
24 | ||
25 | ``fd`` | |
26 | File descriptor returned by :ref:`open() <func-open>`. | |
27 | ||
5377d91f | 28 | ``argp`` |
1473c75e | 29 | Pointer to struct :c:type:`v4l2_cropcap`. |
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30 | |
31 | ||
15e7d615 | 32 | Description |
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33 | =========== |
34 | ||
35 | Applications use this function to query the cropping limits, the pixel | |
36 | aspect of images and to calculate scale factors. They set the ``type`` | |
37 | field of a v4l2_cropcap structure to the respective buffer (stream) | |
2212ff25 | 38 | type and call the :ref:`VIDIOC_CROPCAP` ioctl with a pointer to this |
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39 | structure. Drivers fill the rest of the structure. The results are |
40 | constant except when switching the video standard. Remember this switch | |
41 | can occur implicit when switching the video input or output. | |
42 | ||
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43 | This ioctl must be implemented for video capture or output devices that |
44 | support cropping and/or scaling and/or have non-square pixels, and for | |
45 | overlay devices. | |
46 | ||
e8be7e97 | 47 | .. c:type:: v4l2_cropcap |
5377d91f | 48 | |
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49 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
50 | ||
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51 | .. flat-table:: struct v4l2_cropcap |
52 | :header-rows: 0 | |
53 | :stub-columns: 0 | |
54 | :widths: 1 1 2 | |
55 | ||
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56 | * - __u32 |
57 | - ``type`` | |
58 | - Type of the data stream, set by the application. Only these types | |
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59 | are valid here: ``V4L2_BUF_TYPE_VIDEO_CAPTURE``, ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``, |
60 | ``V4L2_BUF_TYPE_VIDEO_OUTPUT``, ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE`` and | |
20b00bbe | 61 | ``V4L2_BUF_TYPE_VIDEO_OVERLAY``. See :c:type:`v4l2_buf_type` and the note below. |
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62 | * - struct :ref:`v4l2_rect <v4l2-rect-crop>` |
63 | - ``bounds`` | |
64 | - Defines the window within capturing or output is possible, this | |
65 | may exclude for example the horizontal and vertical blanking | |
66 | areas. The cropping rectangle cannot exceed these limits. Width | |
67 | and height are defined in pixels, the driver writer is free to | |
68 | choose origin and units of the coordinate system in the analog | |
69 | domain. | |
70 | * - struct :ref:`v4l2_rect <v4l2-rect-crop>` | |
71 | - ``defrect`` | |
72 | - Default cropping rectangle, it shall cover the "whole picture". | |
73 | Assuming pixel aspect 1/1 this could be for example a 640 × 480 | |
74 | rectangle for NTSC, a 768 × 576 rectangle for PAL and SECAM | |
75 | centered over the active picture area. The same co-ordinate system | |
76 | as for ``bounds`` is used. | |
77 | * - struct :c:type:`v4l2_fract` | |
78 | - ``pixelaspect`` | |
79 | - This is the pixel aspect (y / x) when no scaling is applied, the | |
80 | ratio of the actual sampling frequency and the frequency required | |
81 | to get square pixels. | |
82 | ||
83 | When cropping coordinates refer to square pixels, the driver sets | |
84 | ``pixelaspect`` to 1/1. Other common values are 54/59 for PAL and | |
85 | SECAM, 11/10 for NTSC sampled according to [:ref:`itu601`]. | |
5377d91f | 86 | |
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87 | .. note:: |
88 | Unfortunately in the case of multiplanar buffer types | |
89 | (``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``) | |
90 | this API was messed up with regards to how the :c:type:`v4l2_cropcap` ``type`` field | |
91 | should be filled in. Some drivers only accepted the ``_MPLANE`` buffer type while | |
92 | other drivers only accepted a non-multiplanar buffer type (i.e. without the | |
93 | ``_MPLANE`` at the end). | |
94 | ||
95 | Starting with kernel 4.13 both variations are allowed. | |
96 | ||
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97 | |
98 | ||
99 | .. _v4l2-rect-crop: | |
100 | ||
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101 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
102 | ||
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103 | .. flat-table:: struct v4l2_rect |
104 | :header-rows: 0 | |
105 | :stub-columns: 0 | |
106 | :widths: 1 1 2 | |
107 | ||
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108 | * - __s32 |
109 | - ``left`` | |
110 | - Horizontal offset of the top, left corner of the rectangle, in | |
111 | pixels. | |
112 | * - __s32 | |
113 | - ``top`` | |
114 | - Vertical offset of the top, left corner of the rectangle, in | |
115 | pixels. | |
116 | * - __u32 | |
117 | - ``width`` | |
118 | - Width of the rectangle, in pixels. | |
119 | * - __u32 | |
120 | - ``height`` | |
121 | - Height of the rectangle, in pixels. | |
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122 | |
123 | ||
15e7d615 | 124 | Return Value |
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125 | ============ |
126 | ||
127 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
128 | appropriately. The generic error codes are described at the | |
129 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
130 | ||
131 | EINVAL | |
e8be7e97 | 132 | The struct :c:type:`v4l2_cropcap` ``type`` is |
5377d91f | 133 | invalid. |
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134 | |
135 | ENODATA | |
136 | Cropping is not supported for this input or output. |