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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>