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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
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Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+.. 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{8.7cm}|
+
+.. 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 co-ordinate 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{8.7cm}|
+
+.. 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.