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
