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+.. -*- coding: utf-8; mode: rst -*-
+
+.. _VIDIOC_G_SELECTION:
+
+********************************************
+ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION
+********************************************
+
+Name
+====
+
+VIDIOC_G_SELECTION - VIDIOC_S_SELECTION - Get or set one of the selection rectangles
+
+
+Synopsis
+========
+
+.. cpp:function:: int ioctl( int fd, int request, struct v4l2_selection *argp )
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``request``
+    VIDIOC_G_SELECTION, VIDIOC_S_SELECTION
+
+``argp``
+
+
+Description
+===========
+
+The ioctls are used to query and configure selection rectangles.
+
+To query the cropping (composing) rectangle set struct
+:ref:`v4l2_selection <v4l2-selection>` ``type`` field to the
+respective buffer type. Do not use the multiplanar buffer types. Use
+``V4L2_BUF_TYPE_VIDEO_CAPTURE`` instead of
+``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE`` and use
+``V4L2_BUF_TYPE_VIDEO_OUTPUT`` instead of
+``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``. The next step is setting the
+value of struct :ref:`v4l2_selection <v4l2-selection>` ``target``
+field to ``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer
+to table :ref:`v4l2-selections-common` or :ref:`selection-api` for
+additional targets. The ``flags`` and ``reserved`` fields of struct
+:ref:`v4l2_selection <v4l2-selection>` are ignored and they must be
+filled with zeros. The driver fills the rest of the structure or returns
+EINVAL error code if incorrect buffer type or target was used. If
+cropping (composing) is not supported then the active rectangle is not
+mutable and it is always equal to the bounds rectangle. Finally, the
+struct :ref:`v4l2_rect <v4l2-rect>` ``r`` rectangle is filled with
+the current cropping (composing) coordinates. The coordinates are
+expressed in driver-dependent units. The only exception are rectangles
+for images in raw formats, whose coordinates are always expressed in
+pixels.
+
+To change the cropping (composing) rectangle set the struct
+:ref:`v4l2_selection <v4l2-selection>` ``type`` field to the
+respective buffer type. Do not use multiplanar buffers. Use
+``V4L2_BUF_TYPE_VIDEO_CAPTURE`` instead of
+``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``. Use
+``V4L2_BUF_TYPE_VIDEO_OUTPUT`` instead of
+``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``. The next step is setting the
+value of struct :ref:`v4l2_selection <v4l2-selection>` ``target`` to
+``V4L2_SEL_TGT_CROP`` (``V4L2_SEL_TGT_COMPOSE``). Please refer to table
+:ref:`v4l2-selections-common` or :ref:`selection-api` for additional
+targets. The struct :ref:`v4l2_rect <v4l2-rect>` ``r`` rectangle need
+to be set to the desired active area. Field struct
+:ref:`v4l2_selection <v4l2-selection>` ``reserved`` is ignored and
+must be filled with zeros. The driver may adjust coordinates of the
+requested rectangle. An application may introduce constraints to control
+rounding behaviour. The struct :ref:`v4l2_selection <v4l2-selection>`
+``flags`` field must be set to one of the following:
+
+-  ``0`` - The driver can adjust the rectangle size freely and shall
+   choose a crop/compose rectangle as close as possible to the requested
+   one.
+
+-  ``V4L2_SEL_FLAG_GE`` - The driver is not allowed to shrink the
+   rectangle. The original rectangle must lay inside the adjusted one.
+
+-  ``V4L2_SEL_FLAG_LE`` - The driver is not allowed to enlarge the
+   rectangle. The adjusted rectangle must lay inside the original one.
+
+-  ``V4L2_SEL_FLAG_GE | V4L2_SEL_FLAG_LE`` - The driver must choose the
+   size exactly the same as in the requested rectangle.
+
+Please refer to :ref:`sel-const-adjust`.
+
+The driver may have to adjusts the requested dimensions against hardware
+limits and other parts as the pipeline, i.e. the bounds given by the
+capture/output window or TV display. The closest possible values of
+horizontal and vertical offset and sizes are chosen according to
+following priority:
+
+1. Satisfy constraints from struct
+   :ref:`v4l2_selection <v4l2-selection>` ``flags``.
+
+2. Adjust width, height, left, and top to hardware limits and
+   alignments.
+
+3. Keep center of adjusted rectangle as close as possible to the
+   original one.
+
+4. Keep width and height as close as possible to original ones.
+
+5. Keep horizontal and vertical offset as close as possible to original
+   ones.
+
+On success the struct :ref:`v4l2_rect <v4l2-rect>` ``r`` field
+contains the adjusted rectangle. When the parameters are unsuitable the
+application may modify the cropping (composing) or image parameters and
+repeat the cycle until satisfactory parameters have been negotiated. If
+constraints flags have to be violated at then ``ERANGE`` is returned. The
+error indicates that *there exist no rectangle* that satisfies the
+constraints.
+
+Selection targets and flags are documented in
+:ref:`v4l2-selections-common`.
+
+
+.. _sel-const-adjust:
+
+.. figure::  vidioc-g-selection_files/constraints.*
+    :alt:    constraints.png
+    :align:  center
+
+    Size adjustments with constraint flags.
+
+    Behaviour of rectangle adjustment for different constraint flags.
+
+
+
+
+.. _v4l2-selection:
+
+.. flat-table:: struct v4l2_selection
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+
+    -  .. row 1
+
+       -  __u32
+
+       -  ``type``
+
+       -  Type of the buffer (from enum
+	  :ref:`v4l2_buf_type <v4l2-buf-type>`).
+
+    -  .. row 2
+
+       -  __u32
+
+       -  ``target``
+
+       -  Used to select between
+	  :ref:`cropping and composing rectangles <v4l2-selections-common>`.
+
+    -  .. row 3
+
+       -  __u32
+
+       -  ``flags``
+
+       -  Flags controlling the selection rectangle adjustments, refer to
+	  :ref:`selection flags <v4l2-selection-flags>`.
+
+    -  .. row 4
+
+       -  struct :ref:`v4l2_rect <v4l2-rect>`
+
+       -  ``r``
+
+       -  The selection rectangle.
+
+    -  .. row 5
+
+       -  __u32
+
+       -  ``reserved[9]``
+
+       -  Reserved fields for future use. Drivers and applications must zero
+	  this array.
+
+
+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
+    Given buffer type ``type`` or the selection target ``target`` is not
+    supported, or the ``flags`` argument is not valid.
+
+ERANGE
+    It is not possible to adjust struct :ref:`v4l2_rect <v4l2-rect>`
+    ``r`` rectangle to satisfy all constraints given in the ``flags``
+    argument.
+
+EBUSY
+    It is not possible to apply change of the selection rectangle at the
+    moment. Usually because streaming is in progress.