168 lines
5.5 KiB
XML
168 lines
5.5 KiB
XML
<refentry id="vidioc-cropcap">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_CROPCAP</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_CROPCAP</refname>
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<refpurpose>Information about the video cropping and scaling abilities</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_cropcap
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*<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_CROPCAP</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>Applications use this function to query the cropping
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limits, the pixel aspect of images and to calculate scale factors.
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They set the <structfield>type</structfield> field of a v4l2_cropcap
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structure to the respective buffer (stream) type and call the
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<constant>VIDIOC_CROPCAP</constant> ioctl with a pointer to this
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structure. Drivers fill the rest of the structure. The results are
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constant except when switching the video standard. Remember this
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switch can occur implicit when switching the video input or
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output.</para>
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<para>This ioctl must be implemented for video capture or output devices that
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support cropping and/or scaling and/or have non-square pixels, and for overlay devices.</para>
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<table pgwide="1" frame="none" id="v4l2-cropcap">
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<title>struct <structname>v4l2_cropcap</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>type</structfield></entry>
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<entry>Type of the data stream, set by the application.
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Only these types are valid here:
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<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>,
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<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant>,
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<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>,
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<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE</constant> and
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<constant>V4L2_BUF_TYPE_VIDEO_OVERLAY</constant>. See <xref linkend="v4l2-buf-type" />.</entry>
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</row>
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<row>
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<entry>struct <link linkend="v4l2-rect-crop">v4l2_rect</link></entry>
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<entry><structfield>bounds</structfield></entry>
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<entry>Defines the window within capturing or output is
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possible, this may exclude for example the horizontal and vertical
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blanking areas. The cropping rectangle cannot exceed these limits.
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Width and height are defined in pixels, the driver writer is free to
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choose origin and units of the coordinate system in the analog
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domain.</entry>
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</row>
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<row>
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<entry>struct <link linkend="v4l2-rect-crop">v4l2_rect</link></entry>
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<entry><structfield>defrect</structfield></entry>
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<entry>Default cropping rectangle, it shall cover the
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"whole picture". Assuming pixel aspect 1/1 this could be for example a
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640 × 480 rectangle for NTSC, a
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768 × 576 rectangle for PAL and SECAM centered over
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the active picture area. The same co-ordinate system as for
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<structfield>bounds</structfield> is used.</entry>
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</row>
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<row>
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<entry>&v4l2-fract;</entry>
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<entry><structfield>pixelaspect</structfield></entry>
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<entry><para>This is the pixel aspect (y / x) when no
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scaling is applied, the ratio of the actual sampling
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frequency and the frequency required to get square
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pixels.</para><para>When cropping coordinates refer to square pixels,
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the driver sets <structfield>pixelaspect</structfield> to 1/1. Other
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common values are 54/59 for PAL and SECAM, 11/10 for NTSC sampled
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according to [<xref linkend="itu601" />].</para></entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<!-- NB this table is duplicated in the overlay chapter. -->
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<table pgwide="1" frame="none" id="v4l2-rect-crop">
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<title>struct <structname>v4l2_rect</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__s32</entry>
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<entry><structfield>left</structfield></entry>
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<entry>Horizontal offset of the top, left corner of the
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rectangle, in pixels.</entry>
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</row>
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<row>
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<entry>__s32</entry>
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<entry><structfield>top</structfield></entry>
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<entry>Vertical offset of the top, left corner of the
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rectangle, in pixels.</entry>
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</row>
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<row>
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<entry>__s32</entry>
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<entry><structfield>width</structfield></entry>
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<entry>Width of the rectangle, in pixels.</entry>
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</row>
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<row>
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<entry>__s32</entry>
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<entry><structfield>height</structfield></entry>
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<entry>Height of the rectangle, in pixels. Width
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and height cannot be negative, the fields are signed for
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hysterical reasons. <!-- video4linux-list@redhat.com
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on 22 Oct 2002 subject "Re:[V4L][patches!] Re:v4l2/kernel-2.5" -->
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</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>The &v4l2-cropcap; <structfield>type</structfield> is
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invalid.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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