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Based on kernel version 3.0.4. Page generated on 2011-10-03 22:07 EST.

	<refentry id="vidioc-g-fbuf">
	  <refmeta>
	    <refentrytitle>ioctl VIDIOC_G_FBUF, VIDIOC_S_FBUF</refentrytitle>
	    &manvol;
	  </refmeta>
	
	  <refnamediv>
	    <refname>VIDIOC_G_FBUF</refname>
	    <refname>VIDIOC_S_FBUF</refname>
	    <refpurpose>Get or set frame buffer overlay parameters</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_framebuffer *<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_framebuffer *<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_FBUF, VIDIOC_S_FBUF</para>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><parameter>argp</parameter></term>
		<listitem>
		  <para></para>
		</listitem>
	      </varlistentry>
	    </variablelist>
	  </refsect1>
	
	  <refsect1>
	    <title>Description</title>
	
	    <para>Applications can use the <constant>VIDIOC_G_FBUF</constant> and
	<constant>VIDIOC_S_FBUF</constant> ioctl to get and set the
	framebuffer parameters for a <link linkend="overlay">Video
	Overlay</link> or <link linkend="osd">Video Output Overlay</link>
	(OSD). The type of overlay is implied by the device type (capture or
	output device) and can be determined with the &VIDIOC-QUERYCAP; ioctl.
	One <filename>/dev/videoN</filename> device must not support both
	kinds of overlay.</para>
	
	    <para>The V4L2 API distinguishes destructive and non-destructive
	overlays. A destructive overlay copies captured video images into the
	video memory of a graphics card. A non-destructive overlay blends
	video images into a VGA signal or graphics into a video signal.
	<wordasword>Video Output Overlays</wordasword> are always
	non-destructive.</para>
	
	    <para>To get the current parameters applications call the
	<constant>VIDIOC_G_FBUF</constant> ioctl with a pointer to a
	<structname>v4l2_framebuffer</structname> structure. The driver fills
	all fields of the structure or returns an &EINVAL; when overlays are
	not supported.</para>
	
	    <para>To set the parameters for a <wordasword>Video Output
	Overlay</wordasword>, applications must initialize the
	<structfield>flags</structfield> field of a struct
	<structname>v4l2_framebuffer</structname>. Since the framebuffer is
	implemented on the TV card all other parameters are determined by the
	driver. When an application calls <constant>VIDIOC_S_FBUF</constant>
	with a pointer to this structure, the driver prepares for the overlay
	and returns the framebuffer parameters as
	<constant>VIDIOC_G_FBUF</constant> does, or it returns an error
	code.</para>
	
	    <para>To set the parameters for a <wordasword>non-destructive
	Video Overlay</wordasword>, applications must initialize the
	<structfield>flags</structfield> field, the
	<structfield>fmt</structfield> substructure, and call
	<constant>VIDIOC_S_FBUF</constant>. Again the driver prepares for the
	overlay and returns the framebuffer parameters as
	<constant>VIDIOC_G_FBUF</constant> does, or it returns an error
	code.</para>
	
	    <para>For a <wordasword>destructive Video Overlay</wordasword>
	applications must additionally provide a
	<structfield>base</structfield> address. Setting up a DMA to a
	random memory location can jeopardize the system security, its
	stability or even damage the hardware, therefore only the superuser
	can set the parameters for a destructive video overlay.</para>
	
	    <!-- NB v4l2_pix_format is also specified in pixfmt.sgml.-->
	
	    <table pgwide="1" frame="none" id="v4l2-framebuffer">
	      <title>struct <structname>v4l2_framebuffer</structname></title>
	      <tgroup cols="4">
		&cs-ustr;
		<tbody valign="top">
		  <row>
		    <entry>__u32</entry>
		    <entry><structfield>capability</structfield></entry>
		    <entry></entry>
		    <entry>Overlay capability flags set by the driver, see
	<xref linkend="framebuffer-cap" />.</entry>
		  </row>
		  <row>
		    <entry>__u32</entry>
		    <entry><structfield>flags</structfield></entry>
		    <entry></entry>
		    <entry>Overlay control flags set by application and
	driver, see <xref linkend="framebuffer-flags" /></entry>
		  </row>
		  <row>
		    <entry>void *</entry>
		    <entry><structfield>base</structfield></entry>
		    <entry></entry>
		    <entry>Physical base address of the framebuffer,
	that is the address of the pixel in the top left corner of the
	framebuffer.<footnote><para>A physical base address may not suit all
	platforms. GK notes in theory we should pass something like PCI device
	+ memory region + offset instead. If you encounter problems please
	discuss on the linux-media mailing list: &v4l-ml;.</para></footnote></entry>
		  </row>
		  <row>
		    <entry></entry>
		    <entry></entry>
		    <entry></entry>
		    <entry>This field is irrelevant to
	<wordasword>non-destructive Video Overlays</wordasword>. For
	<wordasword>destructive Video Overlays</wordasword> applications must
	provide a base address. The driver may accept only base addresses
	which are a multiple of two, four or eight bytes. For
	<wordasword>Video Output Overlays</wordasword> the driver must return
	a valid base address, so applications can find the corresponding Linux
	framebuffer device (see <xref linkend="osd" />).</entry>
		  </row>
		  <row>
		    <entry>&v4l2-pix-format;</entry>
		    <entry><structfield>fmt</structfield></entry>
		    <entry></entry>
		    <entry>Layout of the frame buffer. The
	<structname>v4l2_pix_format</structname> structure is defined in <xref
	linkend="pixfmt" />, for clarification the fields and acceptable values
		    are listed below:</entry>
		  </row>
		  <row>
		    <entry></entry>
		    <entry>__u32</entry>
		    <entry><structfield>width</structfield></entry>
		    <entry>Width of the frame buffer in pixels.</entry>
		  </row>
		  <row>
		    <entry></entry>
		    <entry>__u32</entry>
		    <entry><structfield>height</structfield></entry>
		    <entry>Height of the frame buffer in pixels.</entry>
		  </row>
		  <row>
		    <entry></entry>
		    <entry>__u32</entry>
		    <entry><structfield>pixelformat</structfield></entry>
		    <entry>The pixel format of the
	framebuffer.</entry>
		  </row>
		  <row>
		    <entry></entry>
		    <entry></entry>
		    <entry></entry>
		    <entry>For <wordasword>non-destructive Video
	Overlays</wordasword> this field only defines a format for the
	&v4l2-window; <structfield>chromakey</structfield> field.</entry>
		  </row>
		  <row>
		    <entry></entry>
		    <entry></entry>
		    <entry></entry>
		    <entry>For <wordasword>destructive Video
	Overlays</wordasword> applications must initialize this field. For
	<wordasword>Video Output Overlays</wordasword> the driver must return
	a valid format.</entry>
		  </row>
		  <row>
		    <entry></entry>
		    <entry></entry>
		    <entry></entry>
		    <entry>Usually this is an RGB format (for example
	<link linkend="V4L2-PIX-FMT-RGB565"><constant>V4L2_PIX_FMT_RGB565</constant></link>)
	but YUV formats (only packed YUV formats when chroma keying is used,
	not including <constant>V4L2_PIX_FMT_YUYV</constant> and
	<constant>V4L2_PIX_FMT_UYVY</constant>) and the
	<constant>V4L2_PIX_FMT_PAL8</constant> format are also permitted. The
	behavior of the driver when an application requests a compressed
	format is undefined. See <xref linkend="pixfmt" /> for information on
	pixel formats.</entry>
		  </row>
		  <row>
		    <entry></entry>
		    <entry>&v4l2-field;</entry>
		    <entry><structfield>field</structfield></entry>
		    <entry>Drivers and applications shall ignore this field.
	If applicable, the field order is selected with the &VIDIOC-S-FMT;
	ioctl, using the <structfield>field</structfield> field of
	&v4l2-window;.</entry>
		  </row>
		  <row>
		    <entry></entry>
		    <entry>__u32</entry>
		    <entry><structfield>bytesperline</structfield></entry>
		    <entry>Distance in bytes between the leftmost pixels in
	two adjacent lines.</entry>
		  </row>
		  <row>
		    <entry spanname="hspan"><para>This field is irrelevant to
	<wordasword>non-destructive Video
	Overlays</wordasword>.</para><para>For <wordasword>destructive Video
	Overlays</wordasword> both applications and drivers can set this field
	to request padding bytes at the end of each line. Drivers however may
	ignore the requested value, returning <structfield>width</structfield>
	times bytes-per-pixel or a larger value required by the hardware. That
	implies applications can just set this field to zero to get a
	reasonable default.</para><para>For <wordasword>Video Output
	Overlays</wordasword> the driver must return a valid
	value.</para><para>Video hardware may access padding bytes, therefore
	they must reside in accessible memory. Consider for example the case
	where padding bytes after the last line of an image cross a system
	page boundary. Capture devices may write padding bytes, the value is
	undefined. Output devices ignore the contents of padding
	bytes.</para><para>When the image format is planar the
	<structfield>bytesperline</structfield> value applies to the largest
	plane and is divided by the same factor as the
	<structfield>width</structfield> field for any smaller planes. For
	example the Cb and Cr planes of a YUV 4:2:0 image have half as many
	padding bytes following each line as the Y plane. To avoid ambiguities
	drivers must return a <structfield>bytesperline</structfield> value
	rounded up to a multiple of the scale factor.</para></entry>
		  </row>
		  <row>
		    <entry></entry>
		    <entry>__u32</entry>
		    <entry><structfield>sizeimage</structfield></entry>
		    <entry><para>This field is irrelevant to
	<wordasword>non-destructive Video Overlays</wordasword>. For
	<wordasword>destructive Video Overlays</wordasword> applications must
	initialize this field. For <wordasword>Video Output
	Overlays</wordasword> the driver must return a valid
	format.</para><para>Together with <structfield>base</structfield> it
	defines the framebuffer memory accessible by the
	driver.</para></entry>
		  </row>
		  <row>
		    <entry></entry>
		    <entry>&v4l2-colorspace;</entry>
		    <entry><structfield>colorspace</structfield></entry>
		    <entry>This information supplements the
	<structfield>pixelformat</structfield> and must be set by the driver,
	see <xref linkend="colorspaces" />.</entry>
		  </row>
		  <row>
		    <entry></entry>
		    <entry>__u32</entry>
		    <entry><structfield>priv</structfield></entry>
		    <entry>Reserved for additional information about custom
	(driver defined) formats. When not used drivers and applications must
	set this field to zero.</entry>
		  </row>
		</tbody>
	      </tgroup>
	    </table>
	
	    <table pgwide="1" frame="none" id="framebuffer-cap">
	      <title>Frame Buffer Capability Flags</title>
	      <tgroup cols="3">
		&cs-def;
		<tbody valign="top">
		  <row>
		    <entry><constant>V4L2_FBUF_CAP_EXTERNOVERLAY</constant></entry>
		    <entry>0x0001</entry>
		    <entry>The device is capable of non-destructive overlays.
	When the driver clears this flag, only destructive overlays are
	supported. There are no drivers yet which support both destructive and
	non-destructive overlays.</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_CAP_CHROMAKEY</constant></entry>
		    <entry>0x0002</entry>
		    <entry>The device supports clipping by chroma-keying the
	images. That is, image pixels replace pixels in the VGA or video
	signal only where the latter assume a certain color. Chroma-keying
	makes no sense for destructive overlays.</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_CAP_LIST_CLIPPING</constant></entry>
		    <entry>0x0004</entry>
		    <entry>The device supports clipping using a list of clip
	rectangles.</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_CAP_BITMAP_CLIPPING</constant></entry>
		    <entry>0x0008</entry>
		    <entry>The device supports clipping using a bit mask.</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_CAP_LOCAL_ALPHA</constant></entry>
		    <entry>0x0010</entry>
		    <entry>The device supports clipping/blending using the
	alpha channel of the framebuffer or VGA signal. Alpha blending makes
	no sense for destructive overlays.</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_CAP_GLOBAL_ALPHA</constant></entry>
		    <entry>0x0020</entry>
		    <entry>The device supports alpha blending using a global
	alpha value. Alpha blending makes no sense for destructive overlays.</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_CAP_LOCAL_INV_ALPHA</constant></entry>
		    <entry>0x0040</entry>
		    <entry>The device supports clipping/blending using the
	inverted alpha channel of the framebuffer or VGA signal. Alpha
	blending makes no sense for destructive overlays.</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_CAP_SRC_CHROMAKEY</constant></entry>
		    <entry>0x0080</entry>
		    <entry>The device supports Source Chroma-keying. Framebuffer pixels
	with the chroma-key colors are replaced by video pixels, which is exactly opposite of
	<constant>V4L2_FBUF_CAP_CHROMAKEY</constant></entry>
		  </row>
		</tbody>
	      </tgroup>
	    </table>
	
	    <table pgwide="1" frame="none" id="framebuffer-flags">
	      <title>Frame Buffer Flags</title>
	      <tgroup cols="3">
		&cs-def;
		<tbody valign="top">
		  <row>
		    <entry><constant>V4L2_FBUF_FLAG_PRIMARY</constant></entry>
		    <entry>0x0001</entry>
		    <entry>The framebuffer is the primary graphics surface.
	In other words, the overlay is destructive. [?]</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_FLAG_OVERLAY</constant></entry>
		    <entry>0x0002</entry>
		    <entry>The frame buffer is an overlay surface the same
	size as the capture. [?]</entry>
		  </row>
		  <row>
		    <entry spanname="hspan">The purpose of
	<constant>V4L2_FBUF_FLAG_PRIMARY</constant> and
	<constant>V4L2_FBUF_FLAG_OVERLAY</constant> was never quite clear.
	Most drivers seem to ignore these flags. For compatibility with the
	<wordasword>bttv</wordasword> driver applications should set the
	<constant>V4L2_FBUF_FLAG_OVERLAY</constant> flag.</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_FLAG_CHROMAKEY</constant></entry>
		    <entry>0x0004</entry>
		    <entry>Use chroma-keying. The chroma-key color is
	determined by the <structfield>chromakey</structfield> field of
	&v4l2-window; and negotiated with the &VIDIOC-S-FMT; ioctl, see <xref
			linkend="overlay" />
	and
		    <xref linkend="osd" />.</entry>
		  </row>
		  <row>
		    <entry spanname="hspan">There are no flags to enable
	clipping using a list of clip rectangles or a bitmap. These methods
	are negotiated with the &VIDIOC-S-FMT; ioctl, see <xref
			linkend="overlay" /> and <xref linkend="osd" />.</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_FLAG_LOCAL_ALPHA</constant></entry>
		    <entry>0x0008</entry>
		    <entry>Use the alpha channel of the framebuffer to clip or
	blend framebuffer pixels with video images. The blend
	function is: output = framebuffer pixel * alpha + video pixel * (1 -
	alpha). The actual alpha depth depends on the framebuffer pixel
	format.</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_FLAG_GLOBAL_ALPHA</constant></entry>
		    <entry>0x0010</entry>
		    <entry>Use a global alpha value to blend the framebuffer
	with video images. The blend function is: output = (framebuffer pixel
	* alpha + video pixel * (255 - alpha)) / 255. The alpha value is
	determined by the <structfield>global_alpha</structfield> field of
	&v4l2-window; and negotiated with the &VIDIOC-S-FMT; ioctl, see <xref
			linkend="overlay" />
	and <xref linkend="osd" />.</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_FLAG_LOCAL_INV_ALPHA</constant></entry>
		    <entry>0x0020</entry>
		    <entry>Like
	<constant>V4L2_FBUF_FLAG_LOCAL_ALPHA</constant>, use the alpha channel
	of the framebuffer to clip or blend framebuffer pixels with video
	images, but with an inverted alpha value. The blend function is:
	output = framebuffer pixel * (1 - alpha) + video pixel * alpha. The
	actual alpha depth depends on the framebuffer pixel format.</entry>
		  </row>
		  <row>
		    <entry><constant>V4L2_FBUF_FLAG_SRC_CHROMAKEY</constant></entry>
		    <entry>0x0040</entry>
		    <entry>Use source chroma-keying. The source chroma-key color is
	determined by the <structfield>chromakey</structfield> field of
	&v4l2-window; and negotiated with the &VIDIOC-S-FMT; ioctl, see <xref
	linkend="overlay" /> and <xref linkend="osd" />.
	Both chroma-keying are mutual exclusive to each other, so same
	<structfield>chromakey</structfield> field of &v4l2-window; is being used.</entry>
		  </row>
		</tbody>
	      </tgroup>
	    </table>
	  </refsect1>
	
	  <refsect1>
	    &return-value;
	
	    <variablelist>
	      <varlistentry>
		<term><errorcode>EPERM</errorcode></term>
		<listitem>
		  <para><constant>VIDIOC_S_FBUF</constant> can only be called
	by a privileged user to negotiate the parameters for a destructive
	overlay.</para>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><errorcode>EBUSY</errorcode></term>
		<listitem>
		  <para>The framebuffer parameters cannot be changed at this
	time because overlay is already enabled, or capturing is enabled
	and the hardware cannot capture and overlay simultaneously.</para>
		</listitem>
	      </varlistentry>
	      <varlistentry>
		<term><errorcode>EINVAL</errorcode></term>
		<listitem>
		  <para>The ioctl is not supported or the
	<constant>VIDIOC_S_FBUF</constant> parameters are unsuitable.</para>
		</listitem>
	      </varlistentry>
	    </variablelist>
	  </refsect1>
	</refentry>
	
	<!--
	Local Variables:
	mode: sgml
	sgml-parent-document: "v4l2.sgml"
	indent-tabs-mode: nil
	End:
	-->

• [ v4l ]
• bayer.pdf
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• crop.pdf
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• vidioc-subdev-g-fmt.xml
• vidioc-subdev-g-frame-interval.xml
• vidioc-subscribe-event.xml
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