diff options
Diffstat (limited to 'Documentation/userspace-api/media/v4l/vidioc-g-selection.rst')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/vidioc-g-selection.rst | 190 |
1 files changed, 190 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-selection.rst b/Documentation/userspace-api/media/v4l/vidioc-g-selection.rst new file mode 100644 index 000000000..2b5b27260 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/vidioc-g-selection.rst @@ -0,0 +1,190 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L + +.. _VIDIOC_G_SELECTION: + +******************************************** +ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION +******************************************** + +Name +==== + +VIDIOC_G_SELECTION - VIDIOC_S_SELECTION - Get or set one of the selection rectangles + +Synopsis +======== + +.. c:macro:: VIDIOC_G_SELECTION + +``int ioctl(int fd, VIDIOC_G_SELECTION, struct v4l2_selection *argp)`` + +.. c:macro:: VIDIOC_S_SELECTION + +``int ioctl(int fd, VIDIOC_S_SELECTION, struct v4l2_selection *argp)`` + +Arguments +========= + +``fd`` + File descriptor returned by :c:func:`open()`. + +``argp`` + Pointer to struct :c:type:`v4l2_selection`. + +Description +=========== + +The ioctls are used to query and configure selection rectangles. + +To query the cropping (composing) rectangle set struct +:c:type:`v4l2_selection` ``type`` field to the +respective buffer type. The next step is setting the +value of struct :c:type:`v4l2_selection` ``target`` +field to ``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer +to table :ref:`v4l2-selections-common` or :ref:`selection-api` for +additional targets. The ``flags`` and ``reserved`` fields of struct +:c:type:`v4l2_selection` are ignored and they must be +filled with zeros. The driver fills the rest of the structure or returns +EINVAL error code if incorrect buffer type or target was used. If +cropping (composing) is not supported then the active rectangle is not +mutable and it is always equal to the bounds rectangle. Finally, the +struct :c:type:`v4l2_rect` ``r`` rectangle is filled with +the current cropping (composing) coordinates. The coordinates are +expressed in driver-dependent units. The only exception are rectangles +for images in raw formats, whose coordinates are always expressed in +pixels. + +To change the cropping (composing) rectangle set the struct +:c:type:`v4l2_selection` ``type`` field to the +respective buffer type. The next step is setting the +value of struct :c:type:`v4l2_selection` ``target`` to +``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer to table +:ref:`v4l2-selections-common` or :ref:`selection-api` for additional +targets. The struct :c:type:`v4l2_rect` ``r`` rectangle need +to be set to the desired active area. Field struct +:c:type:`v4l2_selection` ``reserved`` is ignored and +must be filled with zeros. The driver may adjust coordinates of the +requested rectangle. An application may introduce constraints to control +rounding behaviour. The struct :c:type:`v4l2_selection` +``flags`` field must be set to one of the following: + +- ``0`` - The driver can adjust the rectangle size freely and shall + choose a crop/compose rectangle as close as possible to the requested + one. + +- ``V4L2_SEL_FLAG_GE`` - The driver is not allowed to shrink the + rectangle. The original rectangle must lay inside the adjusted one. + +- ``V4L2_SEL_FLAG_LE`` - The driver is not allowed to enlarge the + rectangle. The adjusted rectangle must lay inside the original one. + +- ``V4L2_SEL_FLAG_GE | V4L2_SEL_FLAG_LE`` - The driver must choose the + size exactly the same as in the requested rectangle. + +Please refer to :ref:`sel-const-adjust`. + +The driver may have to adjusts the requested dimensions against hardware +limits and other parts as the pipeline, i.e. the bounds given by the +capture/output window or TV display. The closest possible values of +horizontal and vertical offset and sizes are chosen according to +following priority: + +1. Satisfy constraints from struct + :c:type:`v4l2_selection` ``flags``. + +2. Adjust width, height, left, and top to hardware limits and + alignments. + +3. Keep center of adjusted rectangle as close as possible to the + original one. + +4. Keep width and height as close as possible to original ones. + +5. Keep horizontal and vertical offset as close as possible to original + ones. + +On success the struct :c:type:`v4l2_rect` ``r`` field +contains the adjusted rectangle. When the parameters are unsuitable the +application may modify the cropping (composing) or image parameters and +repeat the cycle until satisfactory parameters have been negotiated. If +constraints flags have to be violated at then ``ERANGE`` is returned. The +error indicates that *there exist no rectangle* that satisfies the +constraints. + +Selection targets and flags are documented in +:ref:`v4l2-selections-common`. + +.. _sel-const-adjust: + +.. kernel-figure:: constraints.svg + :alt: constraints.svg + :align: center + + Size adjustments with constraint flags. + + Behaviour of rectangle adjustment for different constraint flags. + + + +.. c:type:: v4l2_selection + +.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}| + +.. flat-table:: struct v4l2_selection + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 2 + + * - __u32 + - ``type`` + - Type of the buffer (from enum + :c:type:`v4l2_buf_type`). + * - __u32 + - ``target`` + - Used to select between + :ref:`cropping and composing rectangles <v4l2-selections-common>`. + * - __u32 + - ``flags`` + - Flags controlling the selection rectangle adjustments, refer to + :ref:`selection flags <v4l2-selection-flags>`. + * - struct :c:type:`v4l2_rect` + - ``r`` + - The selection rectangle. + * - __u32 + - ``reserved[9]`` + - Reserved fields for future use. Drivers and applications must zero + this array. + +.. note:: + Unfortunately in the case of multiplanar buffer types + (``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``) + this API was messed up with regards to how the :c:type:`v4l2_selection` ``type`` field + should be filled in. Some drivers only accepted the ``_MPLANE`` buffer type while + other drivers only accepted a non-multiplanar buffer type (i.e. without the + ``_MPLANE`` at the end). + + Starting with kernel 4.13 both variations are allowed. + +Return Value +============ + +On success 0 is returned, on error -1 and the ``errno`` variable is set +appropriately. The generic error codes are described at the +:ref:`Generic Error Codes <gen-errors>` chapter. + +EINVAL + Given buffer type ``type`` or the selection target ``target`` is not + supported, or the ``flags`` argument is not valid. + +ERANGE + It is not possible to adjust struct :c:type:`v4l2_rect` + ``r`` rectangle to satisfy all constraints given in the ``flags`` + argument. + +ENODATA + Selection is not supported for this input or output. + +EBUSY + It is not possible to apply change of the selection rectangle at the + moment. Usually because streaming is in progress. |