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diff --git a/Documentation/userspace-api/media/v4l/vidioc-cropcap.rst b/Documentation/userspace-api/media/v4l/vidioc-cropcap.rst new file mode 100644 index 000000000..00c31410d --- /dev/null +++ b/Documentation/userspace-api/media/v4l/vidioc-cropcap.rst @@ -0,0 +1,133 @@ +.. 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. |