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+<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>struct</entry>
+	    <entry><structfield>fmt</structfield></entry>
+	    <entry></entry>
+	    <entry>Layout of the frame buffer.</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 first
+plane and is divided by the same factor as the
+<structfield>width</structfield> field for the other 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. 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. Video Output Overlays are in practice always
+non-destructive.</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. Video pixels
+with the chroma-key colors are replaced by framebuffer 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. This flag is typically set by any
+driver that doesn't have the <constant>V4L2_FBUF_CAP_EXTERNOVERLAY</constant>
+capability and it is cleared otherwise.</entry>
+	  </row>
+	  <row>
+	    <entry><constant>V4L2_FBUF_FLAG_OVERLAY</constant></entry>
+	    <entry>0x0002</entry>
+	    <entry>If this flag is set for a video capture device, then the
+driver will set the initial overlay size to cover the full framebuffer size,
+otherwise the existing overlay size (as set by &VIDIOC-S-FMT;) will be used.
+
+Only one video capture driver (bttv) supports this flag. The use of this flag
+for capture devices is deprecated. There is no way to detect which drivers
+support this flag, so the only reliable method of setting the overlay size is
+through &VIDIOC-S-FMT;.
+
+If this flag is set for a video output device, then the video output overlay
+window is relative to the top-left corner of the framebuffer and restricted
+to the size of the framebuffer. If it is cleared, then the video output
+overlay window is relative to the video output display.
+            </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>EINVAL</errorcode></term>
+	<listitem>
+	  <para>The <constant>VIDIOC_S_FBUF</constant> parameters are unsuitable.</para>
+	</listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+</refentry>