137 строки
4.2 KiB
ReStructuredText
137 строки
4.2 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_CROPCAP:
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********************
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ioctl VIDIOC_CROPCAP
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********************
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Name
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====
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VIDIOC_CROPCAP - Information about the video cropping and scaling abilities
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Synopsis
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========
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.. c:function:: int ioctl( int fd, VIDIOC_CROPCAP, struct v4l2_cropcap *argp )
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:name: VIDIOC_CROPCAP
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <func-open>`.
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``argp``
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Pointer to struct :c:type:`v4l2_cropcap`.
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Description
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===========
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Applications use this function to query the cropping limits, the pixel
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aspect of images and to calculate scale factors. They set the ``type``
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field of a v4l2_cropcap structure to the respective buffer (stream)
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type and call the :ref:`VIDIOC_CROPCAP` ioctl with a pointer to this
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structure. Drivers fill the rest of the structure. The results are
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constant except when switching the video standard. Remember this switch
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can occur implicit when switching the video input or output.
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This ioctl must be implemented for video capture or output devices that
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support cropping and/or scaling and/or have non-square pixels, and for
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overlay devices.
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.. c:type:: v4l2_cropcap
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. flat-table:: struct v4l2_cropcap
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u32
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- ``type``
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- Type of the data stream, set by the application. Only these types
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are valid here: ``V4L2_BUF_TYPE_VIDEO_CAPTURE``, ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``,
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``V4L2_BUF_TYPE_VIDEO_OUTPUT``, ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE`` and
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``V4L2_BUF_TYPE_VIDEO_OVERLAY``. See :c:type:`v4l2_buf_type` and the note above.
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* - struct :ref:`v4l2_rect <v4l2-rect-crop>`
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- ``bounds``
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- Defines the window within capturing or output is possible, this
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may exclude for example the horizontal and vertical blanking
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areas. The cropping rectangle cannot exceed these limits. Width
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and height are defined in pixels, the driver writer is free to
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choose origin and units of the coordinate system in the analog
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domain.
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* - struct :ref:`v4l2_rect <v4l2-rect-crop>`
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- ``defrect``
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- Default cropping rectangle, it shall cover the "whole picture".
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Assuming pixel aspect 1/1 this could be for example a 640 × 480
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rectangle for NTSC, a 768 × 576 rectangle for PAL and SECAM
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centered over the active picture area. The same co-ordinate system
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as for ``bounds`` is used.
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* - struct :c:type:`v4l2_fract`
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- ``pixelaspect``
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- This is the pixel aspect (y / x) when no scaling is applied, the
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ratio of the actual sampling frequency and the frequency required
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to get square pixels.
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When cropping coordinates refer to square pixels, the driver sets
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``pixelaspect`` to 1/1. Other common values are 54/59 for PAL and
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SECAM, 11/10 for NTSC sampled according to [:ref:`itu601`].
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.. note::
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Unfortunately in the case of multiplanar buffer types
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(``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``)
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this API was messed up with regards to how the :c:type:`v4l2_cropcap` ``type`` field
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should be filled in. Some drivers only accepted the ``_MPLANE`` buffer type while
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other drivers only accepted a non-multiplanar buffer type (i.e. without the
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``_MPLANE`` at the end).
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Starting with kernel 4.13 both variations are allowed.
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.. _v4l2-rect-crop:
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. flat-table:: struct v4l2_rect
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __s32
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- ``left``
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- Horizontal offset of the top, left corner of the rectangle, in
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pixels.
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* - __s32
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- ``top``
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- Vertical offset of the top, left corner of the rectangle, in
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pixels.
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* - __u32
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- ``width``
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- Width of the rectangle, in pixels.
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* - __u32
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- ``height``
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- Height of the rectangle, in pixels.
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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EINVAL
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The struct :c:type:`v4l2_cropcap` ``type`` is
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invalid.
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ENODATA
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Cropping is not supported for this input or output.
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