<wordasword>format</wordasword> means the combination of media bus data
format, frame width and frame height.</para></note>
- <para>Image formats are typically negotiated on video capture and output
- devices using the <link linkend="crop">cropping and scaling</link> ioctls.
- The driver is responsible for configuring every block in the video pipeline
- according to the requested format at the pipeline input and/or
- output.</para>
+ <para>Image formats are typically negotiated on video capture and
+ output devices using the format and <link
+ linkend="vidioc-subdev-g-selection">selection</link> ioctls. The
+ driver is responsible for configuring every block in the video
+ pipeline according to the requested format at the pipeline input
+ and/or output.</para>
<para>For complex devices, such as often found in embedded systems,
identical image sizes at the output of a pipeline can be achieved using
</section>
<section>
- <title>Cropping and scaling</title>
+ <title>Selections: cropping, scaling and composition</title>
<para>Many sub-devices support cropping frames on their input or output
pads (or possible even on both). Cropping is used to select the area of
- interest in an image, typically on a video sensor or video decoder. It can
+ interest in an image, typically on an image sensor or a video decoder. It can
also be used as part of digital zoom implementations to select the area of
the image that will be scaled up.</para>
&v4l2-rect; by the coordinates of the top left corner and the rectangle
size. Both the coordinates and sizes are expressed in pixels.</para>
- <para>The crop rectangle is retrieved and set using the
- &VIDIOC-SUBDEV-G-CROP; and &VIDIOC-SUBDEV-S-CROP; ioctls. Like for pad
- formats, drivers store try and active crop rectangles. The format
- negotiation mechanism applies to crop settings as well.</para>
-
- <para>On input pads, cropping is applied relatively to the current pad
- format. The pad format represents the image size as received by the
- sub-device from the previous block in the pipeline, and the crop rectangle
- represents the sub-image that will be transmitted further inside the
- sub-device for processing. The crop rectangle be entirely containted
- inside the input image size.</para>
-
- <para>Input crop rectangle are reset to their default value when the input
- image format is modified. Drivers should use the input image size as the
- crop rectangle default value, but hardware requirements may prevent this.
- </para>
+ <para>As for pad formats, drivers store try and active
+ rectangles for the selection targets of ACTUAL type <xref
+ linkend="v4l2-subdev-selection-targets">.</xref></para>
+
+ <para>On sink pads, cropping is applied relative to the
+ current pad format. The pad format represents the image size as
+ received by the sub-device from the previous block in the
+ pipeline, and the crop rectangle represents the sub-image that
+ will be transmitted further inside the sub-device for
+ processing.</para>
+
+ <para>The scaling operation changes the size of the image by
+ scaling it to new dimensions. The scaling ratio isn't specified
+ explicitly, but is implied from the original and scaled image
+ sizes. Both sizes are represented by &v4l2-rect;.</para>
+
+ <para>Scaling support is optional. When supported by a subdev,
+ the crop rectangle on the subdev's sink pad is scaled to the
+ size configured using the &VIDIOC-SUBDEV-S-SELECTION; IOCTL
+ using <constant>V4L2_SUBDEV_SEL_COMPOSE_ACTUAL</constant>
+ selection target on the same pad. If the subdev supports scaling
+ but not composing, the top and left values are not used and must
+ always be set to zero.</para>
+
+ <para>On source pads, cropping is similar to sink pads, with the
+ exception that the source size from which the cropping is
+ performed, is the COMPOSE rectangle on the sink pad. In both
+ sink and source pads, the crop rectangle must be entirely
+ contained inside the source image size for the crop
+ operation.</para>
+
+ <para>The drivers should always use the closest possible
+ rectangle the user requests on all selection targets, unless
+ specifically told otherwise.
+ <constant>V4L2_SUBDEV_SEL_FLAG_SIZE_GE</constant> and
+ <constant>V4L2_SUBDEV_SEL_FLAG_SIZE_LE</constant> flags may be
+ used to round the image size either up or down. <xref
+ linkend="v4l2-subdev-selection-flags"></xref></para>
+ </section>
+
+ <section>
+ <title>Types of selection targets</title>
+
+ <section>
+ <title>ACTUAL targets</title>
+
+ <para>ACTUAL targets reflect the actual hardware configuration
+ at any point of time. There is a BOUNDS target
+ corresponding to every ACTUAL.</para>
+ </section>
+
+ <section>
+ <title>BOUNDS targets</title>
+
+ <para>BOUNDS targets is the smallest rectangle that contains
+ all valid ACTUAL rectangles. It may not be possible to set the
+ ACTUAL rectangle as large as the BOUNDS rectangle, however.
+ This may be because e.g. a sensor's pixel array is not
+ rectangular but cross-shaped or round. The maximum size may
+ also be smaller than the BOUNDS rectangle.</para>
+ </section>
- <para>Cropping behaviour on output pads is not defined.</para>
+ </section>
+
+ <section>
+ <title>Order of configuration and format propagation</title>
+
+ <para>Inside subdevs, the order of image processing steps will
+ always be from the sink pad towards the source pad. This is also
+ reflected in the order in which the configuration must be
+ performed by the user: the changes made will be propagated to
+ any subsequent stages. If this behaviour is not desired, the
+ user must set
+ <constant>V4L2_SUBDEV_SEL_FLAG_KEEP_CONFIG</constant> flag. This
+ flag causes no propagation of the changes are allowed in any
+ circumstances. This may also cause the accessed rectangle to be
+ adjusted by the driver, depending on the properties of the
+ underlying hardware.</para>
+
+ <para>The coordinates to a step always refer to the actual size
+ of the previous step. The exception to this rule is the source
+ compose rectangle, which refers to the sink compose bounds
+ rectangle --- if it is supported by the hardware.</para>
+
+ <orderedlist>
+ <listitem>Sink pad format. The user configures the sink pad
+ format. This format defines the parameters of the image the
+ entity receives through the pad for further processing.</listitem>
+
+ <listitem>Sink pad actual crop selection. The sink pad crop
+ defines the crop performed to the sink pad format.</listitem>
+
+ <listitem>Sink pad actual compose selection. The size of the
+ sink pad compose rectangle defines the scaling ratio compared
+ to the size of the sink pad crop rectangle. The location of
+ the compose rectangle specifies the location of the actual
+ sink compose rectangle in the sink compose bounds
+ rectangle.</listitem>
+
+ <listitem>Source pad actual crop selection. Crop on the source
+ pad defines crop performed to the image in the sink compose
+ bounds rectangle.</listitem>
+
+ <listitem>Source pad format. The source pad format defines the
+ output pixel format of the subdev, as well as the other
+ parameters with the exception of the image width and height.
+ Width and height are defined by the size of the source pad
+ actual crop selection.</listitem>
+ </orderedlist>
+
+ <para>Accessing any of the above rectangles not supported by the
+ subdev will return <constant>EINVAL</constant>. Any rectangle
+ referring to a previous unsupported rectangle coordinates will
+ instead refer to the previous supported rectangle. For example,
+ if sink crop is not supported, the compose selection will refer
+ to the sink pad format dimensions instead.</para>
+
+ <figure id="subdev-image-processing-crop">
+ <title>Image processing in subdevs: simple crop example</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="subdev-image-processing-crop.svg"
+ format="SVG" scale="200" />
+ </imageobject>
+ </mediaobject>
+ </figure>
+
+ <para>In the above example, the subdev supports cropping on its
+ sink pad. To configure it, the user sets the media bus format on
+ the subdev's sink pad. Now the actual crop rectangle can be set
+ on the sink pad --- the location and size of this rectangle
+ reflect the location and size of a rectangle to be cropped from
+ the sink format. The size of the sink crop rectangle will also
+ be the size of the format of the subdev's source pad.</para>
+
+ <figure id="subdev-image-processing-scaling-multi-source">
+ <title>Image processing in subdevs: scaling with multiple sources</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="subdev-image-processing-scaling-multi-source.svg"
+ format="SVG" scale="200" />
+ </imageobject>
+ </mediaobject>
+ </figure>
+
+ <para>In this example, the subdev is capable of first cropping,
+ then scaling and finally cropping for two source pads
+ individually from the resulting scaled image. The location of
+ the scaled image in the cropped image is ignored in sink compose
+ target. Both of the locations of the source crop rectangles
+ refer to the sink scaling rectangle, independently cropping an
+ area at location specified by the source crop rectangle from
+ it.</para>
+
+ <figure id="subdev-image-processing-full">
+ <title>Image processing in subdevs: scaling and composition
+ with multiple sinks and sources</title>
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="subdev-image-processing-full.svg"
+ format="SVG" scale="200" />
+ </imageobject>
+ </mediaobject>
+ </figure>
+
+ <para>The subdev driver supports two sink pads and two source
+ pads. The images from both of the sink pads are individually
+ cropped, then scaled and further composed on the composition
+ bounds rectangle. From that, two independent streams are cropped
+ and sent out of the subdev from the source pads.</para>
</section>
+
</section>
&sub-subdev-formats;
--- /dev/null
+<refentry id="vidioc-subdev-g-selection">
+ <refmeta>
+ <refentrytitle>ioctl VIDIOC_SUBDEV_G_SELECTION, VIDIOC_SUBDEV_S_SELECTION</refentrytitle>
+ &manvol;
+ </refmeta>
+
+ <refnamediv>
+ <refname>VIDIOC_SUBDEV_G_SELECTION</refname>
+ <refname>VIDIOC_SUBDEV_S_SELECTION</refname>
+ <refpurpose>Get or set selection rectangles on a subdev pad</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_subdev_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_SUBDEV_G_SELECTION, VIDIOC_SUBDEV_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 selections are used to configure various image
+ processing functionality performed by the subdevs which affect the
+ image size. This currently includes cropping, scaling and
+ composition.</para>
+
+ <para>The selection API replaces <link
+ linkend="vidioc-subdev-g-crop">the old subdev crop API</link>. All
+ the function of the crop API, and more, are supported by the
+ selections API.</para>
+
+ <para>See <xref linkend="subdev"></xref> for
+ more information on how each selection target affects the image
+ processing pipeline inside the subdevice.</para>
+
+ <section>
+ <title>Types of selection targets</title>
+
+ <para>There are two types of selection targets: actual and bounds.
+ The ACTUAL targets are the targets which configure the hardware.
+ The BOUNDS target will return a rectangle that contain all
+ possible ACTUAL rectangles.</para>
+ </section>
+
+ <section>
+ <title>Discovering supported features</title>
+
+ <para>To discover which targets are supported, the user can
+ perform <constant>VIDIOC_SUBDEV_G_SELECTION</constant> on them.
+ Any unsupported target will return
+ <constant>EINVAL</constant>.</para>
+ </section>
+
+ <table pgwide="1" frame="none" id="v4l2-subdev-selection-targets">
+ <title>V4L2 subdev selection targets</title>
+ <tgroup cols="3">
+ &cs-def;
+ <tbody valign="top">
+ <row>
+ <entry><constant>V4L2_SUBDEV_SEL_TGT_CROP_ACTUAL</constant></entry>
+ <entry>0x0000</entry>
+ <entry>Actual crop. Defines the cropping
+ performed by the processing step.</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_SUBDEV_SEL_TGT_CROP_BOUNDS</constant></entry>
+ <entry>0x0002</entry>
+ <entry>Bounds of the crop rectangle.</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_SUBDEV_SEL_TGT_COMPOSE_ACTUAL</constant></entry>
+ <entry>0x0100</entry>
+ <entry>Actual compose rectangle. Used to configure scaling
+ on sink pads and composition on source pads.</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_SUBDEV_SEL_TGT_COMPOSE_BOUNDS</constant></entry>
+ <entry>0x0102</entry>
+ <entry>Bounds of the compose rectangle.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ <table pgwide="1" frame="none" id="v4l2-subdev-selection-flags">
+ <title>V4L2 subdev selection flags</title>
+ <tgroup cols="3">
+ &cs-def;
+ <tbody valign="top">
+ <row>
+ <entry><constant>V4L2_SUBDEV_SEL_FLAG_SIZE_GE</constant></entry>
+ <entry>(1 << 0)</entry> <entry>Suggest the driver it
+ should choose greater or equal rectangle (in size) than
+ was requested. Albeit the driver may choose a lesser size,
+ it will only do so due to hardware limitations. Without
+ this flag (and
+ <constant>V4L2_SUBDEV_SEL_FLAG_SIZE_LE</constant>) the
+ behaviour is to choose the closest possible
+ rectangle.</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_SUBDEV_SEL_FLAG_SIZE_LE</constant></entry>
+ <entry>(1 << 1)</entry> <entry>Suggest the driver it
+ should choose lesser or equal rectangle (in size) than was
+ requested. Albeit the driver may choose a greater size, it
+ will only do so due to hardware limitations.</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_SUBDEV_SEL_FLAG_KEEP_CONFIG</constant></entry>
+ <entry>(1 << 2)</entry>
+ <entry>The configuration should not be propagated to any
+ further processing steps. If this flag is not given, the
+ configuration is propagated inside the subdevice to all
+ further processing steps.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ <table pgwide="1" frame="none" id="v4l2-subdev-selection">
+ <title>struct <structname>v4l2_subdev_selection</structname></title>
+ <tgroup cols="3">
+ &cs-str;
+ <tbody valign="top">
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>which</structfield></entry>
+ <entry>Active or try selection, from
+ &v4l2-subdev-format-whence;.</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>pad</structfield></entry>
+ <entry>Pad number as reported by the media framework.</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>target</structfield></entry>
+ <entry>Target selection rectangle. See
+ <xref linkend="v4l2-subdev-selection-targets">.</xref>.</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>flags</structfield></entry>
+ <entry>Flags. See
+ <xref linkend="v4l2-subdev-selection-flags">.</xref></entry>
+ </row>
+ <row>
+ <entry>&v4l2-rect;</entry>
+ <entry><structfield>rect</structfield></entry>
+ <entry>Selection rectangle, in pixels.</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>reserved</structfield>[8]</entry>
+ <entry>Reserved for future extensions. Applications and drivers must
+ set the array to zero.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ </refsect1>
+
+ <refsect1>
+ &return-value;
+
+ <variablelist>
+ <varlistentry>
+ <term><errorcode>EBUSY</errorcode></term>
+ <listitem>
+ <para>The selection rectangle can't be changed because the
+ pad is currently busy. This can be caused, for instance, by
+ an active video stream on the pad. The ioctl must not be
+ retried without performing another action to fix the problem
+ first. Only returned by
+ <constant>VIDIOC_SUBDEV_S_SELECTION</constant></para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><errorcode>EINVAL</errorcode></term>
+ <listitem>
+ <para>The &v4l2-subdev-selection;
+ <structfield>pad</structfield> references a non-existing
+ pad, the <structfield>which</structfield> field references a
+ non-existing format, or the selection target is not
+ supported on the given subdev pad.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+</refentry>
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