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[media] doc: v4l: add documentation for selection API 

This patch adds a documentation for VIDIOC_{G/S}_SELECTION ioctl. Moreover, the
patch adds the description of modeling of composing, cropping and scaling
features in V4L2. Finally, some examples are presented.

Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Tomasz Stanislawski 2011-08-19 07:00:04 -03:00 committed by Mauro Carvalho Chehab
parent 15e9ff3fcd
commit 8af4922fe5
5 changed files with 643 additions and 0 deletions
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2
Documentation/DocBook/media/v4l/common.xml
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@ -1168,6 +1168,8 @@ dheight = format.fmt.pix.height;
</section>
</section>
&sub-selection-api;
<section id="streaming-par">
<title>Streaming Parameters</title>

9
Documentation/DocBook/media/v4l/compat.xml
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@ -2376,6 +2376,12 @@ that used it. It was originally scheduled for removal in 2.6.35.
<listitem>
<para>V4L2_CTRL_FLAG_VOLATILE was added to signal volatile controls to userspace.</para>
</listitem>
<listitem>
<para>Add selection API for extended control over cropping and
composing. Does not affect the compatibility of current drivers and
applications. See <link linkend="selection-api"> selection API </link> for
details.</para>
</listitem>
</orderedlist>
</section>
@ -2500,6 +2506,9 @@ ioctls.</para>
<listitem>
<para>&VIDIOC-CREATE-BUFS; and &VIDIOC-PREPARE-BUF; ioctls.</para>
</listitem>
<listitem>
<para>Selection API. <xref linkend="selection-api" /></para>
</listitem>
</itemizedlist>
</section>

327
Documentation/DocBook/media/v4l/selection-api.xml Normal file
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@ -0,0 +1,327 @@
<section id="selection-api">
<title>Experimental API for cropping, composing and scaling</title>
<note>
<title>Experimental</title>
<para>This is an <link linkend="experimental">experimental</link>
interface and may change in the future.</para>
</note>
<section>
<title>Introduction</title>
<para>Some video capture devices can sample a subsection of a picture and
shrink or enlarge it to an image of arbitrary size. Next, the devices can
insert the image into larger one. Some video output devices can crop part of an
input image, scale it up or down and insert it at an arbitrary scan line and
horizontal offset into a video signal. We call these abilities cropping,
scaling and composing.</para>
<para>On a video <emphasis>capture</emphasis> device the source is a video
signal, and the cropping target determine the area actually sampled. The sink
is an image stored in a memory buffer. The composing area specifies which part
of the buffer is actually written to by the hardware. </para>
<para>On a video <emphasis>output</emphasis> device the source is an image in a
memory buffer, and the cropping target is a part of an image to be shown on a
display. The sink is the display or the graphics screen. The application may
select the part of display where the image should be displayed. The size and
position of such a window is controlled by the compose target.</para>
<para>Rectangles for all cropping and composing targets are defined even if the
device does supports neither cropping nor composing. Their size and position
will be fixed in such a case. If the device does not support scaling then the
cropping and composing rectangles have the same size.</para>
</section>
<section>
<title>Selection targets</title>
<figure id="sel-targets-capture">
<title>Cropping and composing targets</title>
<mediaobject>
<imageobject>
<imagedata fileref="selection.png" format="PNG" />
</imageobject>
<textobject>
<phrase>Targets used by a cropping, composing and scaling
process</phrase>
</textobject>
</mediaobject>
</figure>
</section>
<section>
<title>Configuration</title>
<para>Applications can use the <link linkend="vidioc-g-selection">selection
API</link> to select an area in a video signal or a buffer, and to query for
default settings and hardware limits.</para>
<para>Video hardware can have various cropping, composing and scaling
limitations. It may only scale up or down, support only discrete scaling
factors, or have different scaling abilities in the horizontal and vertical
directions. Also it may not support scaling at all. At the same time the
cropping/composing rectangles may have to be aligned, and both the source and
the sink may have arbitrary upper and lower size limits. Therefore, as usual,
drivers are expected to adjust the requested parameters and return the actual
values selected. An application can control the rounding behaviour using <link
linkend="v4l2-sel-flags"> constraint flags </link>.</para>
<section>
<title>Configuration of video capture</title>
<para>See figure <xref linkend="sel-targets-capture" /> for examples of the
selection targets available for a video capture device. It is recommended to
configure the cropping targets before to the composing targets.</para>
<para>The range of coordinates of the top left corner, width and height of
areas that can be sampled is given by the <constant> V4L2_SEL_TGT_CROP_BOUNDS
</constant> target. It is recommended for the driver developers to put the
top/left corner at position <constant> (0,0) </constant>. The rectangle's
coordinates are expressed in driver dependant units, although the coordinate
system guarantees that if sizes of the active cropping and the active composing
rectangles are equal then no scaling is performed. </para>
<para>The top left corner, width and height of the source rectangle, that is
the area actually sampled, is given by the <constant> V4L2_SEL_TGT_CROP_ACTIVE
</constant> target. It uses the same coordinate system as <constant>
V4L2_SEL_TGT_CROP_BOUNDS </constant>. The active cropping area must lie
completely inside the capture boundaries. The driver may further adjust the
requested size and/or position according to hardware limitations.</para>
<para>Each capture device has a default source rectangle, given by the
<constant> V4L2_SEL_TGT_CROP_DEFAULT </constant> target. This rectangle shall
over what the driver writer considers the complete picture. Drivers shall set
the active crop rectangle to the default when the driver is first loaded, but
not later.</para>
<para>The composing targets refer to a memory buffer. The limits of composing
coordinates are obtained using <constant> V4L2_SEL_TGT_COMPOSE_BOUNDS
</constant>. All coordinates are expressed in natural unit for given formats.
Pixels are highly recommended. The rectangle's top/left corner must be located
at position <constant> (0,0) </constant>. The width and height are equal to the
image size set by <constant> VIDIOC_S_FMT </constant>.</para>
<para>The part of a buffer into which the image is inserted by the hardware is
controlled by the <constant> V4L2_SEL_TGT_COMPOSE_ACTIVE </constant> target.
The rectangle's coordinates are also expressed in the same coordinate system as
the bounds rectangle. The composing rectangle must lie completely inside bounds
rectangle. The driver must adjust the composing rectangle to fit to the
bounding limits. Moreover, the driver can perform other adjustments according
to hardware limitations. The application can control rounding behaviour using
<link linkend="v4l2-sel-flags"> constraint flags </link>.</para>
<para>For capture devices the default composing rectangle is queried using
<constant> V4L2_SEL_TGT_COMPOSE_DEFAULT </constant>. It is usually equal to the
bounding rectangle.</para>
<para>The part of a buffer that is modified by the hardware is given by
<constant> V4L2_SEL_TGT_COMPOSE_PADDED </constant>. It contains all pixels
defined using <constant> V4L2_SEL_TGT_COMPOSE_ACTIVE </constant> plus all
padding data modified by hardware during insertion process. All pixels outside
this rectangle <emphasis>must not</emphasis> be changed by the hardware. The
content of pixels that lie inside the padded area but outside active area is
undefined. The application can use the padded and active rectangles to detect
where the rubbish pixels are located and remove them if needed.</para>
</section>
<section>
<title>Configuration of video output</title>
<para>For output devices targets and ioctls are used similarly to the video
capture case. The <emphasis> composing </emphasis> rectangle refers to the
insertion of an image into a video signal. The cropping rectangles refer to a
memory buffer. It is recommended to configure the composing targets before to
the cropping targets.</para>
<para>The cropping targets refer to the memory buffer that contains an image to
be inserted into a video signal or graphical screen. The limits of cropping
coordinates are obtained using <constant> V4L2_SEL_TGT_CROP_BOUNDS </constant>.
All coordinates are expressed in natural units for a given format. Pixels are
highly recommended. The top/left corner is always point <constant> (0,0)
</constant>. The width and height is equal to the image size specified using
<constant> VIDIOC_S_FMT </constant> ioctl.</para>
<para>The top left corner, width and height of the source rectangle, that is
the area from which image date are processed by the hardware, is given by the
<constant> V4L2_SEL_TGT_CROP_ACTIVE </constant>. Its coordinates are expressed
in in the same coordinate system as the bounds rectangle. The active cropping
area must lie completely inside the crop boundaries and the driver may further
adjust the requested size and/or position according to hardware
limitations.</para>
<para>For output devices the default cropping rectangle is queried using
<constant> V4L2_SEL_TGT_CROP_DEFAULT </constant>. It is usually equal to the
bounding rectangle.</para>
<para>The part of a video signal or graphics display where the image is
inserted by the hardware is controlled by <constant> V4L2_SEL_TGT_COMPOSE_ACTIVE
</constant> target. The rectangle's coordinates are expressed in driver
dependant units. The only exception are digital outputs where the units are
pixels. For other types of devices, the coordinate system guarantees that if
sizes of the active cropping and the active composing rectangles are equal then
no scaling is performed. The composing rectangle must lie completely inside
the bounds rectangle. The driver must adjust the area to fit to the bounding
limits. Moreover, the driver can perform other adjustments according to
hardware limitations. </para>
<para>The device has a default composing rectangle, given by the <constant>
V4L2_SEL_TGT_COMPOSE_DEFAULT </constant> target. This rectangle shall cover what
the driver writer considers the complete picture. It is recommended for the
driver developers to put the top/left corner at position <constant> (0,0)
</constant>. Drivers shall set the active composing rectangle to the default
one when the driver is first loaded.</para>
<para>The devices may introduce additional content to video signal other than
an image from memory buffers. It includes borders around an image. However,
such a padded area is driver-dependent feature not covered by this document.
Driver developers are encouraged to keep padded rectangle equal to active one.
The padded target is accessed by the <constant> V4L2_SEL_TGT_COMPOSE_PADDED
</constant> identifier. It must contain all pixels from the <constant>
V4L2_SEL_TGT_COMPOSE_ACTIVE </constant> target.</para>
</section>
<section>
<title>Scaling control.</title>
<para>An application can detect if scaling is performed by comparing the width
and the height of rectangles obtained using <constant> V4L2_SEL_TGT_CROP_ACTIVE
</constant> and <constant> V4L2_SEL_TGT_COMPOSE_ACTIVE </constant> targets. If
these are not equal then the scaling is applied. The application can compute
the scaling ratios using these values.</para>
</section>
</section>
<section>
<title>Comparison with old cropping API.</title>
<para>The selection API was introduced to cope with deficiencies of previous
<link linkend="crop"> API </link>, that was designed to control simple capture
devices. Later the cropping API was adopted by video output drivers. The ioctls
are used to select a part of the display were the video signal is inserted. It
should be considered as an API abuse because the described operation is
actually the composing. The selection API makes a clear distinction between
composing and cropping operations by setting the appropriate targets. The V4L2
API lacks any support for composing to and cropping from an image inside a
memory buffer. The application could configure a capture device to fill only a
part of an image by abusing V4L2 API. Cropping a smaller image from a larger
one is achieved by setting the field <structfield>
&v4l2-pix-format;::bytesperline </structfield>. Introducing an image offsets
could be done by modifying field <structfield> &v4l2-buffer;::m:userptr
</structfield> before calling <constant> VIDIOC_QBUF </constant>. Those
operations should be avoided because they are not portable (endianness), and do
not work for macroblock and Bayer formats and mmap buffers. The selection API
deals with configuration of buffer cropping/composing in a clear, intuitive and
portable way. Next, with the selection API the concepts of the padded target
and constraints flags are introduced. Finally, <structname> &v4l2-crop;
</structname> and <structname> &v4l2-cropcap; </structname> have no reserved
fields. Therefore there is no way to extend their functionality. The new
<structname> &v4l2-selection; </structname> provides a lot of place for future
extensions. Driver developers are encouraged to implement only selection API.
The former cropping API would be simulated using the new one. </para>
</section>
<section>
<title>Examples</title>
<example>
<title>Resetting the cropping parameters</title>
<para>(A video capture device is assumed; change <constant>
V4L2_BUF_TYPE_VIDEO_CAPTURE </constant> for other devices; change target to
<constant> V4L2_SEL_TGT_COMPOSE_* </constant> family to configure composing
area)</para>
<programlisting>
&v4l2-selection; sel = {
.type = V4L2_BUF_TYPE_VIDEO_CAPTURE,
.target = V4L2_SEL_TGT_CROP_DEFAULT,
};
ret = ioctl(fd, &VIDIOC-G-SELECTION;, &amp;sel);
if (ret)
exit(-1);
sel.target = V4L2_SEL_TGT_CROP_ACTIVE;
ret = ioctl(fd, &VIDIOC-S-SELECTION;, &amp;sel);
if (ret)
exit(-1);
</programlisting>
</example>
<example>
<title>Simple downscaling</title>
<para>Setting a composing area on output of size of <emphasis> at most
</emphasis> half of limit placed at a center of a display.</para>
<programlisting>
&v4l2-selection; sel = {
.type = V4L2_BUF_TYPE_VIDEO_OUTPUT,
.target = V4L2_SEL_TGT_COMPOSE_BOUNDS,
};
struct v4l2_rect r;
ret = ioctl(fd, &VIDIOC-G-SELECTION;, &amp;sel);
if (ret)
exit(-1);
/* setting smaller compose rectangle */
r.width = sel.r.width / 2;
r.height = sel.r.height / 2;
r.left = sel.r.width / 4;
r.top = sel.r.height / 4;
sel.r = r;
sel.target = V4L2_SEL_TGT_COMPOSE_ACTIVE;
sel.flags = V4L2_SEL_FLAG_LE;
ret = ioctl(fd, &VIDIOC-S-SELECTION;, &amp;sel);
if (ret)
exit(-1);
</programlisting>
</example>
<example>
<title>Querying for scaling factors</title>
<para>A video output device is assumed; change <constant>
V4L2_BUF_TYPE_VIDEO_OUTPUT </constant> for other devices</para>
<programlisting>
&v4l2-selection; compose = {
.type = V4L2_BUF_TYPE_VIDEO_OUTPUT,
.target = V4L2_SEL_TGT_COMPOSE_ACTIVE,
};
&v4l2-selection; crop = {
.type = V4L2_BUF_TYPE_VIDEO_OUTPUT,
.target = V4L2_SEL_TGT_CROP_ACTIVE,
};
double hscale, vscale;
ret = ioctl(fd, &VIDIOC-G-SELECTION;, &amp;compose);
if (ret)
exit(-1);
ret = ioctl(fd, &VIDIOC-G-SELECTION;, &amp;crop);
if (ret)
exit(-1);
/* computing scaling factors */
hscale = (double)compose.r.width / crop.r.width;
vscale = (double)compose.r.height / crop.r.height;
</programlisting>
</example>
</section>
</section>

1
Documentation/DocBook/media/v4l/v4l2.xml
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@ -501,6 +501,7 @@ and discussions on the V4L mailing list.</revremark>
&sub-g-output;
&sub-g-parm;
&sub-g-priority;
&sub-g-selection;
&sub-g-sliced-vbi-cap;
&sub-g-std;
&sub-g-tuner;

304
Documentation/DocBook/media/v4l/vidioc-g-selection.xml Normal file
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@ -0,0 +1,304 @@
<refentry id="vidioc-g-selection">
<refmeta>
<refentrytitle>ioctl VIDIOC_G_SELECTION, VIDIOC_S_SELECTION</refentrytitle>
&manvol;
</refmeta>
<refnamediv>
<refname>VIDIOC_G_SELECTION</refname>
<refname>VIDIOC_S_SELECTION</refname>
<refpurpose>Get or set one of the selection rectangles</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>ioctl</function></funcdef>
<paramdef>int <parameter>fd</parameter></paramdef>
<paramdef>int <parameter>request</parameter></paramdef>
<paramdef>struct v4l2_selection *<parameter>argp</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Arguments</title>
<variablelist>
<varlistentry>
<term><parameter>fd</parameter></term>
<listitem>
<para>&fd;</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>request</parameter></term>
<listitem>
<para>VIDIOC_G_SELECTION, VIDIOC_S_SELECTION</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>argp</parameter></term>
<listitem>
<para></para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Description</title>
<note>
<title>Experimental</title>
<para>This is an <link linkend="experimental"> experimental </link>
interface and may change in the future.</para>
</note>
<para>The ioctls are used to query and configure selection rectangles.</para>
<para> To query the cropping (composing) rectangle set <structfield>
&v4l2-selection;::type </structfield> to the respective buffer type. Do not
use multiplanar buffers. Use <constant> V4L2_BUF_TYPE_VIDEO_CAPTURE
</constant> instead of <constant> V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE
</constant>. Use <constant> V4L2_BUF_TYPE_VIDEO_OUTPUT </constant> instead of
<constant> V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE </constant>. The next step is
setting <structfield> &v4l2-selection;::target </structfield> to value
<constant> V4L2_SEL_TGT_CROP_ACTIVE </constant> (<constant>
V4L2_SEL_TGT_COMPOSE_ACTIVE </constant>). Please refer to table <xref
linkend="v4l2-sel-target" /> or <xref linkend="selection-api" /> for additional
targets. Fields <structfield> &v4l2-selection;::flags </structfield> and
<structfield> &v4l2-selection;::reserved </structfield> are ignored and they
must be filled with zeros. The driver fills the rest of the structure or
returns &EINVAL; 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, structure <structfield>
&v4l2-selection;::r </structfield> 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. </para>
<para> To change the cropping (composing) rectangle set <structfield>
&v4l2-selection;::type </structfield> to the respective buffer type. Do not
use multiplanar buffers. Use <constant> V4L2_BUF_TYPE_VIDEO_CAPTURE
</constant> instead of <constant> V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE
</constant>. Use <constant> V4L2_BUF_TYPE_VIDEO_OUTPUT </constant> instead of
<constant> V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE </constant>. The next step is
setting <structfield> &v4l2-selection;::target </structfield> to value
<constant> V4L2_SEL_TGT_CROP_ACTIVE </constant> (<constant>
V4L2_SEL_TGT_COMPOSE_ACTIVE </constant>). Please refer to table <xref
linkend="v4l2-sel-target" /> or <xref linkend="selection-api" /> for additional
targets. Set desired active area into the field <structfield>
&v4l2-selection;::r </structfield>. Field <structfield>
&v4l2-selection;::reserved </structfield> is ignored and must be filled with
zeros. The driver may adjust the rectangle coordinates. An application may
introduce constraints to control rounding behaviour. Set the field
<structfield> &v4l2-selection;::flags </structfield> to one of values:
<itemizedlist>
<listitem>
<para><constant>0</constant> - The driver can adjust the rectangle size freely
and shall choose a crop/compose rectangle as close as possible to the requested
one.</para>
</listitem>
<listitem>
<para><constant>V4L2_SEL_FLAG_GE</constant> - The driver is not allowed to
shrink the rectangle. The original rectangle must lay inside the adjusted
one.</para>
</listitem>
<listitem>
<para><constant>V4L2_SEL_FLAG_LE</constant> - The driver is not allowed to
enlarge the rectangle. The adjusted rectangle must lay inside the original
one.</para>
</listitem>
<listitem>
<para><constant>V4L2_SEL_FLAG_GE | V4L2_SEL_FLAG_LE</constant> - The driver
must choose the size exactly the same as in the requested rectangle.</para>
</listitem>
</itemizedlist>
Please refer to <xref linkend="sel-const-adjust" />.
</para>
<para> 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:
<orderedlist>
<listitem>
<para>Satisfy constraints from <structfield>&v4l2-selection;::flags</structfield>.</para>
</listitem>
<listitem>
<para>Adjust width, height, left, and top to hardware limits and alignments.</para>
</listitem>
<listitem>
<para>Keep center of adjusted rectangle as close as possible to the original one.</para>
</listitem>
<listitem>
<para>Keep width and height as close as possible to original ones.</para>
</listitem>
<listitem>
<para>Keep horizontal and vertical offset as close as possible to original ones.</para>
</listitem>
</orderedlist>
On success the field <structfield> &v4l2-selection;::r </structfield> 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 <emphasis> there
exist no rectangle </emphasis> that satisfies the constraints.</para>
</refsect1>
<refsect1>
<table frame="none" pgwide="1" id="v4l2-sel-target">
<title>Selection targets.</title>
<tgroup cols="3">
&cs-def;
<tbody valign="top">
<row>
<entry><constant>V4L2_SEL_TGT_CROP_ACTIVE</constant></entry>
<entry>0</entry>
<entry>area that is currently cropped by hardware</entry>
</row>
<row>
<entry><constant>V4L2_SEL_TGT_CROP_DEFAULT</constant></entry>
<entry>1</entry>
<entry>suggested cropping rectangle that covers the "whole picture"</entry>
</row>
<row>
<entry><constant>V4L2_SEL_TGT_CROP_BOUNDS</constant></entry>
<entry>2</entry>
<entry>limits for the cropping rectangle</entry>
</row>
<row>
<entry><constant>V4L2_SEL_TGT_COMPOSE_ACTIVE</constant></entry>
<entry>256</entry>
<entry>area to which data are composed by hardware</entry>
</row>
<row>
<entry><constant>V4L2_SEL_TGT_COMPOSE_DEFAULT</constant></entry>
<entry>257</entry>
<entry>suggested composing rectangle that covers the "whole picture"</entry>
</row>
<row>
<entry><constant>V4L2_SEL_TGT_COMPOSE_BOUNDS</constant></entry>
<entry>258</entry>
<entry>limits for the composing rectangle</entry>
</row>
<row>
<entry><constant>V4L2_SEL_TGT_COMPOSE_PADDED</constant></entry>
<entry>259</entry>
<entry>the active area and all padding pixels that are inserted or modified by the hardware</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1>
<table frame="none" pgwide="1" id="v4l2-sel-flags">
<title>Selection constraint flags</title>
<tgroup cols="3">
&cs-def;
<tbody valign="top">
<row>
<entry><constant>V4L2_SEL_FLAG_GE</constant></entry>
<entry>0x00000001</entry>
<entry>indicate that adjusted rectangle must contain a rectangle from <structfield>&v4l2-selection;::r</structfield></entry>
</row>
<row>
<entry><constant>V4L2_SEL_FLAG_LE</constant></entry>
<entry>0x00000002</entry>
<entry>indicate that adjusted rectangle must be inside a rectangle from <structfield>&v4l2-selection;::r</structfield></entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<section>
<figure id="sel-const-adjust">
<title>Size adjustments with constraint flags.</title>
<mediaobject>
<imageobject>
<imagedata fileref="constraints.png" format="PNG" />
</imageobject>
<textobject>
<phrase>Behaviour of rectangle adjustment for different constraint
flags.</phrase>
</textobject>
</mediaobject>
</figure>
</section>
<refsect1>
<table pgwide="1" frame="none" id="v4l2-selection">
<title>struct <structname>v4l2_selection</structname></title>
<tgroup cols="3">
&cs-str;
<tbody valign="top">
<row>
<entry>__u32</entry>
<entry><structfield>type</structfield></entry>
<entry>Type of the buffer (from &v4l2-buf-type;)</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>target</structfield></entry>
<entry>used to select between <link linkend="v4l2-sel-target"> cropping and composing rectangles </link></entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>flags</structfield></entry>
<entry>control over coordinates adjustments, refer to <link linkend="v4l2-sel-flags">selection flags</link></entry>
</row>
<row>
<entry>&v4l2-rect;</entry>
<entry><structfield>r</structfield></entry>
<entry>selection rectangle</entry>
</row>
<row>
<entry>__u32</entry>
<entry><structfield>reserved[9]</structfield></entry>
<entry>Reserved fields for future use</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1>
&return-value;
<variablelist>
<varlistentry>
<term><errorcode>EINVAL</errorcode></term>
<listitem>
<para>The buffer <structfield> &v4l2-selection;::type </structfield>
or <structfield> &v4l2-selection;::target </structfield> is not supported, or
the <structfield> &v4l2-selection;::flags </structfield> are invalid.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><errorcode>ERANGE</errorcode></term>
<listitem>
<para>it is not possible to adjust a rectangle <structfield>
&v4l2-selection;::r </structfield> that satisfies all contraints from
<structfield> &v4l2-selection;::flags </structfield>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><errorcode>EBUSY</errorcode></term>
<listitem>
<para>it is not possible to apply change of selection rectangle at the moment.
Usually because streaming is in progress.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
</refentry>