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.
|