134 lines
4.2 KiB
ReStructuredText
134 lines
4.2 KiB
ReStructuredText
|
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
|
|||
|
|
.. c:namespace:: V4L
|
|||
|
|
|
|||
|
|
.. _VIDIOC_CROPCAP:
|
|||
|
|
|
|||
|
|
********************
|
|||
|
|
ioctl VIDIOC_CROPCAP
|
|||
|
|
********************
|
|||
|
|
|
|||
|
|
Name
|
|||
|
|
====
|
|||
|
|
|
|||
|
|
VIDIOC_CROPCAP - Information about the video cropping and scaling abilities
|
|||
|
|
|
|||
|
|
Synopsis
|
|||
|
|
========
|
|||
|
|
|
|||
|
|
.. c:macro:: VIDIOC_CROPCAP
|
|||
|
|
|
|||
|
|
``int ioctl(int fd, VIDIOC_CROPCAP, struct v4l2_cropcap *argp)``
|
|||
|
|
|
|||
|
|
Arguments
|
|||
|
|
=========
|
|||
|
|
|
|||
|
|
``fd``
|
|||
|
|
File descriptor returned by :c:func:`open()`.
|
|||
|
|
|
|||
|
|
``argp``
|
|||
|
|
Pointer to struct :c:type:`v4l2_cropcap`.
|
|||
|
|
|
|||
|
|
Description
|
|||
|
|
===========
|
|||
|
|
|
|||
|
|
Applications use this function to query the cropping limits, the pixel
|
|||
|
|
aspect of images and to calculate scale factors. They set the ``type``
|
|||
|
|
field of a v4l2_cropcap structure to the respective buffer (stream)
|
|||
|
|
type and call the :ref:`VIDIOC_CROPCAP` ioctl with a pointer to this
|
|||
|
|
structure. Drivers fill the rest of the structure. The results are
|
|||
|
|
constant except when switching the video standard. Remember this switch
|
|||
|
|
can occur implicit when switching the video input or output.
|
|||
|
|
|
|||
|
|
This ioctl must be implemented for video capture or output devices that
|
|||
|
|
support cropping and/or scaling and/or have non-square pixels, and for
|
|||
|
|
overlay devices.
|
|||
|
|
|
|||
|
|
.. c:type:: v4l2_cropcap
|
|||
|
|
|
|||
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
|
|||
|
|
|
|||
|
|
.. flat-table:: struct v4l2_cropcap
|
|||
|
|
:header-rows: 0
|
|||
|
|
:stub-columns: 0
|
|||
|
|
:widths: 1 1 2
|
|||
|
|
|
|||
|
|
* - __u32
|
|||
|
|
- ``type``
|
|||
|
|
- Type of the data stream, set by the application. Only these types
|
|||
|
|
are valid here: ``V4L2_BUF_TYPE_VIDEO_CAPTURE``, ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``,
|
|||
|
|
``V4L2_BUF_TYPE_VIDEO_OUTPUT``, ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE`` and
|
|||
|
|
``V4L2_BUF_TYPE_VIDEO_OVERLAY``. See :c:type:`v4l2_buf_type` and the note below.
|
|||
|
|
* - struct :ref:`v4l2_rect <v4l2-rect-crop>`
|
|||
|
|
- ``bounds``
|
|||
|
|
- Defines the window within capturing or output is possible, this
|
|||
|
|
may exclude for example the horizontal and vertical blanking
|
|||
|
|
areas. The cropping rectangle cannot exceed these limits. Width
|
|||
|
|
and height are defined in pixels, the driver writer is free to
|
|||
|
|
choose origin and units of the coordinate system in the analog
|
|||
|
|
domain.
|
|||
|
|
* - struct :ref:`v4l2_rect <v4l2-rect-crop>`
|
|||
|
|
- ``defrect``
|
|||
|
|
- Default cropping rectangle, it shall cover the "whole picture".
|
|||
|
|
Assuming pixel aspect 1/1 this could be for example a 640 × 480
|
|||
|
|
rectangle for NTSC, a 768 × 576 rectangle for PAL and SECAM
|
|||
|
|
centered over the active picture area. The same coordinate system
|
|||
|
|
as for ``bounds`` is used.
|
|||
|
|
* - struct :c:type:`v4l2_fract`
|
|||
|
|
- ``pixelaspect``
|
|||
|
|
- This is the pixel aspect (y / x) when no scaling is applied, the
|
|||
|
|
ratio of the actual sampling frequency and the frequency required
|
|||
|
|
to get square pixels.
|
|||
|
|
|
|||
|
|
When cropping coordinates refer to square pixels, the driver sets
|
|||
|
|
``pixelaspect`` to 1/1. Other common values are 54/59 for PAL and
|
|||
|
|
SECAM, 11/10 for NTSC sampled according to [:ref:`itu601`].
|
|||
|
|
|
|||
|
|
.. 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_cropcap` ``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.
|
|||
|
|
|
|||
|
|
|
|||
|
|
.. _v4l2-rect-crop:
|
|||
|
|
|
|||
|
|
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
|
|||
|
|
|
|||
|
|
.. flat-table:: struct v4l2_rect
|
|||
|
|
:header-rows: 0
|
|||
|
|
:stub-columns: 0
|
|||
|
|
:widths: 1 1 2
|
|||
|
|
|
|||
|
|
* - __s32
|
|||
|
|
- ``left``
|
|||
|
|
- Horizontal offset of the top, left corner of the rectangle, in
|
|||
|
|
pixels.
|
|||
|
|
* - __s32
|
|||
|
|
- ``top``
|
|||
|
|
- Vertical offset of the top, left corner of the rectangle, in
|
|||
|
|
pixels.
|
|||
|
|
* - __u32
|
|||
|
|
- ``width``
|
|||
|
|
- Width of the rectangle, in pixels.
|
|||
|
|
* - __u32
|
|||
|
|
- ``height``
|
|||
|
|
- Height of the rectangle, in pixels.
|
|||
|
|
|
|||
|
|
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
|
|||
|
|
The struct :c:type:`v4l2_cropcap` ``type`` is
|
|||
|
|
invalid.
|
|||
|
|
|
|||
|
|
ENODATA
|
|||
|
|
Cropping is not supported for this input or output.
|