457 lines
17 KiB
XML
457 lines
17 KiB
XML
<refentry id="vidioc-g-fbuf">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_G_FBUF, VIDIOC_S_FBUF</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_G_FBUF</refname>
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<refname>VIDIOC_S_FBUF</refname>
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<refpurpose>Get or set frame buffer overlay parameters</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_framebuffer *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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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>const struct v4l2_framebuffer *<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_G_FBUF, VIDIOC_S_FBUF</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 can use the <constant>VIDIOC_G_FBUF</constant> and
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<constant>VIDIOC_S_FBUF</constant> ioctl to get and set the
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framebuffer parameters for a <link linkend="overlay">Video
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Overlay</link> or <link linkend="osd">Video Output Overlay</link>
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(OSD). The type of overlay is implied by the device type (capture or
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output device) and can be determined with the &VIDIOC-QUERYCAP; ioctl.
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One <filename>/dev/videoN</filename> device must not support both
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kinds of overlay.</para>
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<para>The V4L2 API distinguishes destructive and non-destructive
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overlays. A destructive overlay copies captured video images into the
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video memory of a graphics card. A non-destructive overlay blends
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video images into a VGA signal or graphics into a video signal.
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<wordasword>Video Output Overlays</wordasword> are always
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non-destructive.</para>
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<para>To get the current parameters applications call the
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<constant>VIDIOC_G_FBUF</constant> ioctl with a pointer to a
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<structname>v4l2_framebuffer</structname> structure. The driver fills
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all fields of the structure or returns an &EINVAL; when overlays are
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not supported.</para>
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<para>To set the parameters for a <wordasword>Video Output
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Overlay</wordasword>, applications must initialize the
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<structfield>flags</structfield> field of a struct
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<structname>v4l2_framebuffer</structname>. Since the framebuffer is
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implemented on the TV card all other parameters are determined by the
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driver. When an application calls <constant>VIDIOC_S_FBUF</constant>
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with a pointer to this structure, the driver prepares for the overlay
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and returns the framebuffer parameters as
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<constant>VIDIOC_G_FBUF</constant> does, or it returns an error
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code.</para>
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<para>To set the parameters for a <wordasword>non-destructive
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Video Overlay</wordasword>, applications must initialize the
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<structfield>flags</structfield> field, the
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<structfield>fmt</structfield> substructure, and call
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<constant>VIDIOC_S_FBUF</constant>. Again the driver prepares for the
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overlay and returns the framebuffer parameters as
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<constant>VIDIOC_G_FBUF</constant> does, or it returns an error
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code.</para>
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<para>For a <wordasword>destructive Video Overlay</wordasword>
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applications must additionally provide a
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<structfield>base</structfield> address. Setting up a DMA to a
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random memory location can jeopardize the system security, its
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stability or even damage the hardware, therefore only the superuser
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can set the parameters for a destructive video overlay.</para>
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<!-- NB v4l2_pix_format is also specified in pixfmt.sgml.-->
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<table pgwide="1" frame="none" id="v4l2-framebuffer">
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<title>struct <structname>v4l2_framebuffer</structname></title>
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<tgroup cols="4">
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&cs-ustr;
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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>capability</structfield></entry>
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<entry></entry>
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<entry>Overlay capability flags set by the driver, see
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<xref linkend="framebuffer-cap" />.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>flags</structfield></entry>
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<entry></entry>
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<entry>Overlay control flags set by application and
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driver, see <xref linkend="framebuffer-flags" /></entry>
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</row>
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<row>
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<entry>void *</entry>
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<entry><structfield>base</structfield></entry>
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<entry></entry>
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<entry>Physical base address of the framebuffer,
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that is the address of the pixel in the top left corner of the
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framebuffer.<footnote><para>A physical base address may not suit all
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platforms. GK notes in theory we should pass something like PCI device
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+ memory region + offset instead. If you encounter problems please
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discuss on the linux-media mailing list: &v4l-ml;.</para></footnote></entry>
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</row>
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<row>
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<entry></entry>
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<entry></entry>
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<entry></entry>
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<entry>This field is irrelevant to
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<wordasword>non-destructive Video Overlays</wordasword>. For
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<wordasword>destructive Video Overlays</wordasword> applications must
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provide a base address. The driver may accept only base addresses
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which are a multiple of two, four or eight bytes. For
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<wordasword>Video Output Overlays</wordasword> the driver must return
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a valid base address, so applications can find the corresponding Linux
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framebuffer device (see <xref linkend="osd" />).</entry>
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</row>
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<row>
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<entry>&v4l2-pix-format;</entry>
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<entry><structfield>fmt</structfield></entry>
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<entry></entry>
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<entry>Layout of the frame buffer. The
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<structname>v4l2_pix_format</structname> structure is defined in <xref
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linkend="pixfmt" />, for clarification the fields and acceptable values
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are listed below:</entry>
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</row>
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<row>
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<entry></entry>
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<entry>__u32</entry>
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<entry><structfield>width</structfield></entry>
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<entry>Width of the frame buffer in pixels.</entry>
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</row>
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<row>
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<entry></entry>
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<entry>__u32</entry>
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<entry><structfield>height</structfield></entry>
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<entry>Height of the frame buffer in pixels.</entry>
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</row>
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<row>
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<entry></entry>
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<entry>__u32</entry>
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<entry><structfield>pixelformat</structfield></entry>
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<entry>The pixel format of the
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framebuffer.</entry>
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</row>
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<row>
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<entry></entry>
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<entry></entry>
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<entry></entry>
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<entry>For <wordasword>non-destructive Video
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Overlays</wordasword> this field only defines a format for the
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&v4l2-window; <structfield>chromakey</structfield> field.</entry>
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</row>
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<row>
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<entry></entry>
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<entry></entry>
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<entry></entry>
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<entry>For <wordasword>destructive Video
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Overlays</wordasword> applications must initialize this field. For
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<wordasword>Video Output Overlays</wordasword> the driver must return
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a valid format.</entry>
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</row>
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<row>
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<entry></entry>
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<entry></entry>
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<entry></entry>
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<entry>Usually this is an RGB format (for example
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<link linkend="V4L2-PIX-FMT-RGB565"><constant>V4L2_PIX_FMT_RGB565</constant></link>)
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but YUV formats (only packed YUV formats when chroma keying is used,
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not including <constant>V4L2_PIX_FMT_YUYV</constant> and
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<constant>V4L2_PIX_FMT_UYVY</constant>) and the
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<constant>V4L2_PIX_FMT_PAL8</constant> format are also permitted. The
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behavior of the driver when an application requests a compressed
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format is undefined. See <xref linkend="pixfmt" /> for information on
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pixel formats.</entry>
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</row>
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<row>
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<entry></entry>
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<entry>&v4l2-field;</entry>
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<entry><structfield>field</structfield></entry>
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<entry>Drivers and applications shall ignore this field.
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If applicable, the field order is selected with the &VIDIOC-S-FMT;
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ioctl, using the <structfield>field</structfield> field of
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&v4l2-window;.</entry>
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</row>
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<row>
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<entry></entry>
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<entry>__u32</entry>
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<entry><structfield>bytesperline</structfield></entry>
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<entry>Distance in bytes between the leftmost pixels in
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two adjacent lines.</entry>
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</row>
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<row>
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<entry spanname="hspan"><para>This field is irrelevant to
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<wordasword>non-destructive Video
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Overlays</wordasword>.</para><para>For <wordasword>destructive Video
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Overlays</wordasword> both applications and drivers can set this field
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to request padding bytes at the end of each line. Drivers however may
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ignore the requested value, returning <structfield>width</structfield>
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times bytes-per-pixel or a larger value required by the hardware. That
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implies applications can just set this field to zero to get a
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reasonable default.</para><para>For <wordasword>Video Output
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Overlays</wordasword> the driver must return a valid
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value.</para><para>Video hardware may access padding bytes, therefore
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they must reside in accessible memory. Consider for example the case
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where padding bytes after the last line of an image cross a system
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page boundary. Capture devices may write padding bytes, the value is
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undefined. Output devices ignore the contents of padding
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bytes.</para><para>When the image format is planar the
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<structfield>bytesperline</structfield> value applies to the largest
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plane and is divided by the same factor as the
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<structfield>width</structfield> field for any smaller planes. For
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example the Cb and Cr planes of a YUV 4:2:0 image have half as many
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padding bytes following each line as the Y plane. To avoid ambiguities
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drivers must return a <structfield>bytesperline</structfield> value
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rounded up to a multiple of the scale factor.</para></entry>
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</row>
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<row>
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<entry></entry>
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<entry>__u32</entry>
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<entry><structfield>sizeimage</structfield></entry>
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<entry><para>This field is irrelevant to
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<wordasword>non-destructive Video Overlays</wordasword>. For
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<wordasword>destructive Video Overlays</wordasword> applications must
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initialize this field. For <wordasword>Video Output
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Overlays</wordasword> the driver must return a valid
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format.</para><para>Together with <structfield>base</structfield> it
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defines the framebuffer memory accessible by the
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driver.</para></entry>
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</row>
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<row>
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<entry></entry>
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<entry>&v4l2-colorspace;</entry>
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<entry><structfield>colorspace</structfield></entry>
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<entry>This information supplements the
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<structfield>pixelformat</structfield> and must be set by the driver,
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see <xref linkend="colorspaces" />.</entry>
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</row>
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<row>
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<entry></entry>
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<entry>__u32</entry>
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<entry><structfield>priv</structfield></entry>
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<entry>Reserved for additional information about custom
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(driver defined) formats. When not used drivers and applications must
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set this field to zero.</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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<table pgwide="1" frame="none" id="framebuffer-cap">
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<title>Frame Buffer Capability Flags</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_FBUF_CAP_EXTERNOVERLAY</constant></entry>
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<entry>0x0001</entry>
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<entry>The device is capable of non-destructive overlays.
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When the driver clears this flag, only destructive overlays are
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supported. There are no drivers yet which support both destructive and
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non-destructive overlays.</entry>
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</row>
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<row>
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<entry><constant>V4L2_FBUF_CAP_CHROMAKEY</constant></entry>
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<entry>0x0002</entry>
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<entry>The device supports clipping by chroma-keying the
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images. That is, image pixels replace pixels in the VGA or video
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signal only where the latter assume a certain color. Chroma-keying
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makes no sense for destructive overlays.</entry>
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</row>
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<row>
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<entry><constant>V4L2_FBUF_CAP_LIST_CLIPPING</constant></entry>
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<entry>0x0004</entry>
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<entry>The device supports clipping using a list of clip
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rectangles.</entry>
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</row>
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<row>
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<entry><constant>V4L2_FBUF_CAP_BITMAP_CLIPPING</constant></entry>
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<entry>0x0008</entry>
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<entry>The device supports clipping using a bit mask.</entry>
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</row>
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<row>
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<entry><constant>V4L2_FBUF_CAP_LOCAL_ALPHA</constant></entry>
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<entry>0x0010</entry>
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<entry>The device supports clipping/blending using the
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alpha channel of the framebuffer or VGA signal. Alpha blending makes
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no sense for destructive overlays.</entry>
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</row>
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<row>
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<entry><constant>V4L2_FBUF_CAP_GLOBAL_ALPHA</constant></entry>
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<entry>0x0020</entry>
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<entry>The device supports alpha blending using a global
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alpha value. Alpha blending makes no sense for destructive overlays.</entry>
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</row>
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<row>
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<entry><constant>V4L2_FBUF_CAP_LOCAL_INV_ALPHA</constant></entry>
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<entry>0x0040</entry>
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<entry>The device supports clipping/blending using the
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inverted alpha channel of the framebuffer or VGA signal. Alpha
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blending makes no sense for destructive overlays.</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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<table pgwide="1" frame="none" id="framebuffer-flags">
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<title>Frame Buffer Flags</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_FBUF_FLAG_PRIMARY</constant></entry>
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<entry>0x0001</entry>
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<entry>The framebuffer is the primary graphics surface.
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In other words, the overlay is destructive. [?]</entry>
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</row>
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<row>
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<entry><constant>V4L2_FBUF_FLAG_OVERLAY</constant></entry>
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<entry>0x0002</entry>
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<entry>The frame buffer is an overlay surface the same
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size as the capture. [?]</entry>
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</row>
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<row>
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<entry spanname="hspan">The purpose of
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<constant>V4L2_FBUF_FLAG_PRIMARY</constant> and
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<constant>V4L2_FBUF_FLAG_OVERLAY</constant> was never quite clear.
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Most drivers seem to ignore these flags. For compatibility with the
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<wordasword>bttv</wordasword> driver applications should set the
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<constant>V4L2_FBUF_FLAG_OVERLAY</constant> flag.</entry>
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</row>
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<row>
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<entry><constant>V4L2_FBUF_FLAG_CHROMAKEY</constant></entry>
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<entry>0x0004</entry>
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<entry>Use chroma-keying. The chroma-key color is
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determined by the <structfield>chromakey</structfield> field of
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&v4l2-window; and negotiated with the &VIDIOC-S-FMT; ioctl, see <xref
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linkend="overlay" />
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and
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<xref linkend="osd" />.</entry>
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</row>
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<row>
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<entry spanname="hspan">There are no flags to enable
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clipping using a list of clip rectangles or a bitmap. These methods
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are negotiated with the &VIDIOC-S-FMT; ioctl, see <xref
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linkend="overlay" /> and <xref linkend="osd" />.</entry>
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</row>
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<row>
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<entry><constant>V4L2_FBUF_FLAG_LOCAL_ALPHA</constant></entry>
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<entry>0x0008</entry>
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<entry>Use the alpha channel of the framebuffer to clip or
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blend framebuffer pixels with video images. The blend
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function is: output = framebuffer pixel * alpha + video pixel * (1 -
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alpha). The actual alpha depth depends on the framebuffer pixel
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format.</entry>
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</row>
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<row>
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<entry><constant>V4L2_FBUF_FLAG_GLOBAL_ALPHA</constant></entry>
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<entry>0x0010</entry>
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<entry>Use a global alpha value to blend the framebuffer
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with video images. The blend function is: output = (framebuffer pixel
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* alpha + video pixel * (255 - alpha)) / 255. The alpha value is
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determined by the <structfield>global_alpha</structfield> field of
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&v4l2-window; and negotiated with the &VIDIOC-S-FMT; ioctl, see <xref
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linkend="overlay" />
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and <xref linkend="osd" />.</entry>
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</row>
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<row>
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<entry><constant>V4L2_FBUF_FLAG_LOCAL_INV_ALPHA</constant></entry>
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<entry>0x0020</entry>
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<entry>Like
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<constant>V4L2_FBUF_FLAG_LOCAL_ALPHA</constant>, use the alpha channel
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of the framebuffer to clip or blend framebuffer pixels with video
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images, but with an inverted alpha value. The blend function is:
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output = framebuffer pixel * (1 - alpha) + video pixel * alpha. The
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actual alpha depth depends on the framebuffer pixel format.</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>EPERM</errorcode></term>
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<listitem>
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<para><constant>VIDIOC_S_FBUF</constant> can only be called
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by a privileged user to negotiate the parameters for a destructive
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overlay.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EBUSY</errorcode></term>
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<listitem>
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<para>The framebuffer parameters cannot be changed at this
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time because overlay is already enabled, or capturing is enabled
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and the hardware cannot capture and overlay simultaneously.</para>
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</listitem>
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</varlistentry>
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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 ioctl is not supported or the
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<constant>VIDIOC_S_FBUF</constant> parameters are unsuitable.</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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<!--
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Local Variables:
|
|
mode: sgml
|
|
sgml-parent-document: "v4l2.sgml"
|
|
indent-tabs-mode: nil
|
|
End:
|
|
-->
|