linux/Documentation/DocBook/media/v4l/vidioc-g-crop.xml

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<refentry id="vidioc-g-crop">
<refmeta>
<refentrytitle>ioctl VIDIOC_G_CROP, VIDIOC_S_CROP</refentrytitle>
&manvol;
</refmeta>
<refnamediv>
<refname>VIDIOC_G_CROP</refname>
<refname>VIDIOC_S_CROP</refname>
<refpurpose>Get or set the current cropping rectangle</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_crop *<parameter>argp</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<funcsynopsis>
<funcprototype>
<funcdef>int <function>ioctl</function></funcdef>
<paramdef>int <parameter>fd</parameter></paramdef>
<paramdef>int <parameter>request</parameter></paramdef>
<paramdef>const struct v4l2_crop *<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_CROP, VIDIOC_S_CROP</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>argp</parameter></term>
<listitem>
<para></para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Description</title>
<para>To query the cropping rectangle size and position
applications set the <structfield>type</structfield> field of a
<structname>v4l2_crop</structname> structure to the respective buffer
(stream) type and call the <constant>VIDIOC_G_CROP</constant> ioctl
with a pointer to this structure. The driver fills the rest of the
structure or returns the &EINVAL; if cropping is not supported.</para>
<para>To change the cropping rectangle applications initialize the
<structfield>type</structfield> and &v4l2-rect; substructure named
<structfield>c</structfield> of a v4l2_crop structure and call the
<constant>VIDIOC_S_CROP</constant> ioctl with a pointer to this
structure.</para>
<para>Do not use the multiplanar buffer types. Use <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>
instead of <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant>
and use <constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant> instead of
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE</constant>.</para>
<para>The driver first adjusts the requested dimensions against
hardware limits, &ie; the bounds given by the capture/output window,
and it rounds to the closest possible values of horizontal and
vertical offset, width and height. In particular the driver must round
the vertical offset of the cropping rectangle to frame lines modulo
two, such that the field order cannot be confused.</para>
<para>Second the driver adjusts the image size (the opposite
rectangle of the scaling process, source or target depending on the
data direction) to the closest size possible while maintaining the
current horizontal and vertical scaling factor.</para>
<para>Finally the driver programs the hardware with the actual
cropping and image parameters. <constant>VIDIOC_S_CROP</constant> is a
write-only ioctl, it does not return the actual parameters. To query
them applications must call <constant>VIDIOC_G_CROP</constant> and
&VIDIOC-G-FMT;. When the parameters are unsuitable the application may
modify the cropping or image parameters and repeat the cycle until
satisfactory parameters have been negotiated.</para>
<para>When cropping is not supported then no parameters are
changed and <constant>VIDIOC_S_CROP</constant> returns the
&EINVAL;.</para>
<table pgwide="1" frame="none" id="v4l2-crop">
<title>struct <structname>v4l2_crop</structname></title>
<tgroup cols="3">
&cs-str;
<tbody valign="top">
<row>
[media] v4l2: use __u32 rather than enums in ioctl() structs V4L2 uses the enum type in IOCTL arguments in IOCTLs that were defined until the use of enum was considered less than ideal. Recently Rémi Denis-Courmont brought up the issue by proposing a patch to convert the enums to unsigned: <URL:http://www.spinics.net/lists/linux-media/msg46167.html> This sparked a long discussion where another solution to the issue was proposed: two sets of IOCTL structures, one with __u32 and the other with enums, and conversion code between the two: <URL:http://www.spinics.net/lists/linux-media/msg47168.html> Both approaches implement a complete solution that resolves the problem. The first one is simple but requires assuming enums and __u32 are the same in size (so we won't break the ABI) while the second one is more complex and less clean but does not require making that assumption. The issue boils down to whether enums are fundamentally different from __u32 or not, and can the former be substituted by the latter. During the discussion it was concluded that the __u32 has the same size as enums on all archs Linux is supported: it has not been shown that replacing those enums in IOCTL arguments would break neither source or binary compatibility. If no such reason is found, just replacing the enums with __u32s is the way to go. This is what this patch does. This patch is slightly different from Remi's first RFC (link above): it uses __u32 instead of unsigned and also changes the arguments of VIDIOC_G_PRIORITY and VIDIOC_S_PRIORITY. Signed-off-by: Rémi Denis-Courmont <remi@remlab.net> Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi> Acked-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
2012-05-10 13:02:07 +08:00
<entry>__u32</entry>
<entry><structfield>type</structfield></entry>
<entry>Type of the data stream, set by the application.
Only these types are valid here: <constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>,
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant> and
<constant>V4L2_BUF_TYPE_VIDEO_OVERLAY</constant>. See <xref linkend="v4l2-buf-type" />.</entry>
</row>
<row>
<entry>&v4l2-rect;</entry>
<entry><structfield>c</structfield></entry>
<entry>Cropping rectangle. The same co-ordinate system as
for &v4l2-cropcap; <structfield>bounds</structfield> is used.</entry>
</row>
</tbody>
</tgroup>
</table>
</refsect1>
<refsect1>
&return-value;
</refsect1>
</refentry>