191 lines
6.4 KiB
ReStructuredText
191 lines
6.4 KiB
ReStructuredText
|
.. 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.
|