doc/spec/r10595.htm

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>Video for Linux Two API Specification: Revision 0.24</TH
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><H1
><A
NAME="VIDIOC-G-FBUF"
></A
>ioctl VIDIOC_G_FBUF, VIDIOC_S_FBUF</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN10599"
></A
><H2
>Name</H2
>VIDIOC_G_FBUF, VIDIOC_S_FBUF&nbsp;--&nbsp;Get or set frame buffer overlay parameters</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN10603"
></A
><H2
>Synopsis</H2
><DIV
CLASS="FUNCSYNOPSIS"
><P
></P
><A
NAME="AEN10604"
></A
><P
><CODE
><CODE
CLASS="FUNCDEF"
>int ioctl</CODE
>(int fd, int request, struct v4l2_framebuffer *argp);</CODE
></P
><P
></P
></DIV
><DIV
CLASS="FUNCSYNOPSIS"
><P
></P
><A
NAME="AEN10614"
></A
><P
><CODE
><CODE
CLASS="FUNCDEF"
>int ioctl</CODE
>(int fd, int request, const struct v4l2_framebuffer *argp);</CODE
></P
><P
></P
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN10624"
></A
><H2
>Arguments</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="PARAMETER"
>fd</CODE
></DT
><DD
><P
>File descriptor returned by <A
HREF="r14090.htm"
><CODE
CLASS="FUNCTION"
>open()</CODE
></A
>.</P
></DD
><DT
><CODE
CLASS="PARAMETER"
>request</CODE
></DT
><DD
><P
>VIDIOC_G_FBUF, VIDIOC_S_FBUF</P
></DD
><DT
><CODE
CLASS="PARAMETER"
>argp</CODE
></DT
><DD
><P
></P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN10644"
></A
><H2
>Description</H2
><P
>Applications can use the <CODE
CLASS="CONSTANT"
>VIDIOC_G_FBUF</CODE
> and
<CODE
CLASS="CONSTANT"
>VIDIOC_S_FBUF</CODE
> ioctl to get and set the
framebuffer parameters for a <A
HREF="x6570.htm"
>Video
Overlay</A
> or <A
HREF="x6909.htm"
>Video Output Overlay</A
>
(OSD). The type of overlay is implied by the device type (capture or
output device) and can be determined with the <A
HREF="r13105.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_QUERYCAP</CODE
></A
> ioctl.
One <TT
CLASS="FILENAME"
>/dev/videoN</TT
> device must not support both
kinds of overlay.</P
><P
>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.
<I
CLASS="WORDASWORD"
>Video Output Overlays</I
> are always
non-destructive.</P
><P
>To get the current parameters applications call the
<CODE
CLASS="CONSTANT"
>VIDIOC_G_FBUF</CODE
> ioctl with a pointer to a
<CODE
CLASS="STRUCTNAME"
>v4l2_framebuffer</CODE
> structure. The driver fills
all fields of the structure or returns an <SPAN
CLASS="ERRORCODE"
>EINVAL</SPAN
> error code when overlays are
not supported.</P
><P
>To set the parameters for a <I
CLASS="WORDASWORD"
>Video Output
Overlay</I
>, applications must initialize the
<CODE
CLASS="STRUCTFIELD"
>flags</CODE
> field of a struct
<CODE
CLASS="STRUCTNAME"
>v4l2_framebuffer</CODE
>. Since the framebuffer is
implemented on the TV card all other parameters are determined by the
driver. When an application calls <CODE
CLASS="CONSTANT"
>VIDIOC_S_FBUF</CODE
>
with a pointer to this structure, the driver prepares for the overlay
and returns the framebuffer parameters as
<CODE
CLASS="CONSTANT"
>VIDIOC_G_FBUF</CODE
> does, or it returns an error
code.</P
><P
>To set the parameters for a <I
CLASS="WORDASWORD"
>non-destructive
Video Overlay</I
>, applications must initialize the
<CODE
CLASS="STRUCTFIELD"
>flags</CODE
> field, the
<CODE
CLASS="STRUCTFIELD"
>fmt</CODE
> substructure, and call
<CODE
CLASS="CONSTANT"
>VIDIOC_S_FBUF</CODE
>. Again the driver prepares for the
overlay and returns the framebuffer parameters as
<CODE
CLASS="CONSTANT"
>VIDIOC_G_FBUF</CODE
> does, or it returns an error
code.</P
><P
>For a <I
CLASS="WORDASWORD"
>destructive Video Overlay</I
>
applications must additionally provide a
<CODE
CLASS="STRUCTFIELD"
>base</CODE
> 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.</P
><DIV
CLASS="TABLE"
><A
NAME="V4L2-FRAMEBUFFER"
></A
><P
><B
>Table 1. struct <CODE
CLASS="STRUCTNAME"
>v4l2_framebuffer</CODE
></B
></P
><TABLE
BORDER="0"
FRAME="void"
WIDTH="100%"
CLASS="CALSTABLE"
><COL
WIDTH="20%"
TITLE="C1"><COL
WIDTH="20%"
TITLE="C2"><COL
WIDTH="20%"
TITLE="C3"><COL
WIDTH="40%"
TITLE="C4"><TBODY
VALIGN="TOP"
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>capability</CODE
></TD
><TD
>&nbsp;</TD
><TD
>Overlay capability flags set by the driver, see
<A
HREF="r10595.htm#FRAMEBUFFER-CAP"
>Table 2</A
>.</TD
></TR
><TR
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>flags</CODE
></TD
><TD
>&nbsp;</TD
><TD
>Overlay control flags set by application and
driver, see <A
HREF="r10595.htm#FRAMEBUFFER-FLAGS"
>Table 3</A
></TD
></TR
><TR
><TD
>void *</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>base</CODE
></TD
><TD
>&nbsp;</TD
><TD
><P
>Physical base address of the framebuffer,
that is the address of the pixel in the top left corner of the
framebuffer.<SUP
>a</SUP
></P
><P
>This field is irrelevant to
<I
CLASS="WORDASWORD"
>non-destructive Video Overlays</I
>. For
<I
CLASS="WORDASWORD"
>destructive Video Overlays</I
> applications must
provide a base address. The driver may accept only base addresses
which are a multiple of two, four or eight bytes. For
<I
CLASS="WORDASWORD"
>Video Output Overlays</I
> the driver must return
a valid base address, so applications can find the corresponding Linux
framebuffer device (see <A
HREF="x6909.htm"
>Section 4.4</A
>).</P
></TD
></TR
><TR
><TD
>struct&nbsp;<A
HREF="c2030.htm#V4L2-PIX-FORMAT"
>v4l2_pix_format</A
></TD
><TD
><CODE
CLASS="STRUCTFIELD"
>fmt</CODE
></TD
><TD
>&nbsp;</TD
><TD
>Layout of the frame buffer. The
<CODE
CLASS="STRUCTNAME"
>v4l2_pix_format</CODE
> structure is defined in <A
HREF="c2030.htm"
>Chapter 2</A
>, for clarification the fields and acceptable values
            are listed below:</TD
></TR
><TR
><TD
>&nbsp;</TD
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>width</CODE
></TD
><TD
>Width of the frame buffer in pixels.</TD
></TR
><TR
><TD
>&nbsp;</TD
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>height</CODE
></TD
><TD
>Height of the frame buffer in pixels.</TD
></TR
><TR
><TD
>&nbsp;</TD
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>pixelformat</CODE
></TD
><TD
><P
>The pixel format of the
framebuffer.</P
><P
>For <I
CLASS="WORDASWORD"
>non-destructive Video
Overlays</I
> this field only defines a format for the
struct&nbsp;<A
HREF="x6570.htm#V4L2-WINDOW"
>v4l2_window</A
> <CODE
CLASS="STRUCTFIELD"
>chromakey</CODE
>
field.</P
><P
>For <I
CLASS="WORDASWORD"
>destructive Video
Overlays</I
> applications must initialize this field. For
<I
CLASS="WORDASWORD"
>Video Output Overlays</I
> the driver must return
a valid format.</P
><P
>Usually this is an RGB format (for example
<A
HREF="r2492.htm#V4L2-PIX-FMT-RGB565"
><CODE
CLASS="CONSTANT"
>V4L2_PIX_FMT_RGB565</CODE
></A
>)
but YUV formats (only packed YUV formats when chroma keying is used,
not including <CODE
CLASS="CONSTANT"
>V4L2_PIX_FMT_YUYV</CODE
> and
<CODE
CLASS="CONSTANT"
>V4L2_PIX_FMT_UYVY</CODE
>) and the
<CODE
CLASS="CONSTANT"
>V4L2_PIX_FMT_PAL8</CODE
> format are also permitted. The
behavior of the driver when an application requests a compressed
format is undefined. See <A
HREF="c2030.htm"
>Chapter 2</A
> for information on
pixel formats.</P
></TD
></TR
><TR
><TD
>&nbsp;</TD
><TD
>enum&nbsp;<A
HREF="x6386.htm#V4L2-FIELD"
>v4l2_field</A
></TD
><TD
><CODE
CLASS="STRUCTFIELD"
>field</CODE
></TD
><TD
>Drivers and applications shall ignore this field.
If applicable, the field order is selected with the <A
HREF="r10944.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_S_FMT</CODE
></A
>
ioctl, using the <CODE
CLASS="STRUCTFIELD"
>field</CODE
> field of
struct&nbsp;<A
HREF="x6570.htm#V4L2-WINDOW"
>v4l2_window</A
>.</TD
></TR
><TR
><TD
>&nbsp;</TD
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>bytesperline</CODE
></TD
><TD
>Distance in bytes between the leftmost pixels in
two adjacent lines.</TD
></TR
><TR
><TD
COLSPAN="4"
><P
>This field is irrelevant to
<I
CLASS="WORDASWORD"
>non-destructive Video
Overlays</I
>.</P
><P
>For <I
CLASS="WORDASWORD"
>destructive Video
Overlays</I
> 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 <CODE
CLASS="STRUCTFIELD"
>width</CODE
>
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.</P
><P
>For <I
CLASS="WORDASWORD"
>Video Output
Overlays</I
> the driver must return a valid
value.</P
><P
>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.</P
><P
>When the image format is planar the
<CODE
CLASS="STRUCTFIELD"
>bytesperline</CODE
> value applies to the largest
plane and is divided by the same factor as the
<CODE
CLASS="STRUCTFIELD"
>width</CODE
> 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 <CODE
CLASS="STRUCTFIELD"
>bytesperline</CODE
> value
rounded up to a multiple of the scale factor.</P
></TD
></TR
><TR
><TD
>&nbsp;</TD
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>sizeimage</CODE
></TD
><TD
><P
>This field is irrelevant to
<I
CLASS="WORDASWORD"
>non-destructive Video Overlays</I
>. For
<I
CLASS="WORDASWORD"
>destructive Video Overlays</I
> applications must
initialize this field. For <I
CLASS="WORDASWORD"
>Video Output
Overlays</I
> the driver must return a valid
format.</P
><P
>Together with <CODE
CLASS="STRUCTFIELD"
>base</CODE
> it
defines the framebuffer memory accessible by the
driver.</P
></TD
></TR
><TR
><TD
>&nbsp;</TD
><TD
>enum&nbsp;<A
HREF="x2123.htm#V4L2-COLORSPACE"
>v4l2_colorspace</A
></TD
><TD
><CODE
CLASS="STRUCTFIELD"
>colorspace</CODE
></TD
><TD
>This information supplements the
<CODE
CLASS="STRUCTFIELD"
>pixelformat</CODE
> and must be set by the driver,
see <A
HREF="x2123.htm"
>Section 2.2</A
>.</TD
></TR
><TR
><TD
>&nbsp;</TD
><TD
>__u32</TD
><TD
><CODE
CLASS="STRUCTFIELD"
>priv</CODE
></TD
><TD
>Reserved for additional information about custom
(driver defined) formats. When not used drivers and applications must
set this field to zero.</TD
></TR
></TBODY
><TR
><TD
COLSPAN="4"
>Notes:<BR><A
NAME="FTN.AEN10706"
>a. </A
>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 Video4Linux mailing list:
<A
HREF="https://listman.redhat.com/mailman/listinfo/video4linux-list"
TARGET="_top"
>https://listman.redhat.com/mailman/listinfo/video4linux-list</A
>.<BR></TD
></TR
></TABLE
></DIV
><DIV
CLASS="TABLE"
><A
NAME="FRAMEBUFFER-CAP"
></A
><P
><B
>Table 2. Frame Buffer Capability Flags</B
></P
><TABLE
BORDER="0"
FRAME="void"
WIDTH="100%"
CLASS="CALSTABLE"
><COL
WIDTH="38%"
TITLE="C1"><COL
WIDTH="12%"
TITLE="C2"><COL
WIDTH="50%"
TITLE="C3"><TBODY
VALIGN="TOP"
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_CAP_EXTERNOVERLAY</CODE
></TD
><TD
>0x0001</TD
><TD
>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.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_CAP_CHROMAKEY</CODE
></TD
><TD
>0x0002</TD
><TD
>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.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_CAP_LIST_CLIPPING</CODE
></TD
><TD
>0x0004</TD
><TD
>The device supports clipping using a list of clip
rectangles.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_CAP_BITMAP_CLIPPING</CODE
></TD
><TD
>0x0008</TD
><TD
>The device supports clipping using a bit mask.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_CAP_LOCAL_ALPHA</CODE
></TD
><TD
>0x0010</TD
><TD
>The device supports clipping/blending using the
alpha channel of the framebuffer or VGA signal. Alpha blending makes
no sense for destructive overlays.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_CAP_GLOBAL_ALPHA</CODE
></TD
><TD
>0x0020</TD
><TD
>The device supports alpha blending using a global
alpha value. Alpha blending makes no sense for destructive overlays.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_CAP_LOCAL_INV_ALPHA</CODE
></TD
><TD
>0x0040</TD
><TD
>The device supports clipping/blending using the
inverted alpha channel of the framebuffer or VGA signal. Alpha
blending makes no sense for destructive overlays.</TD
></TR
></TBODY
></TABLE
></DIV
><DIV
CLASS="TABLE"
><A
NAME="FRAMEBUFFER-FLAGS"
></A
><P
><B
>Table 3. Frame Buffer Flags</B
></P
><TABLE
BORDER="0"
FRAME="void"
WIDTH="100%"
CLASS="CALSTABLE"
><COL
WIDTH="38%"
TITLE="C1"><COL
WIDTH="12%"
TITLE="C2"><COL
WIDTH="50%"
TITLE="C3"><TBODY
VALIGN="TOP"
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_FLAG_PRIMARY</CODE
></TD
><TD
>0x0001</TD
><TD
>The framebuffer is the primary graphics surface.
In other words, the overlay is destructive. [?]</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_FLAG_OVERLAY</CODE
></TD
><TD
>0x0002</TD
><TD
>The frame buffer is an overlay surface the same
size as the capture. [?]</TD
></TR
><TR
><TD
COLSPAN="3"
>The purpose of
<CODE
CLASS="CONSTANT"
>V4L2_FBUF_FLAG_PRIMARY</CODE
> and
<CODE
CLASS="CONSTANT"
>V4L2_FBUF_FLAG_OVERLAY</CODE
> was never quite clear.
Most drivers seem to ignore these flags. For compatibility with the
<I
CLASS="WORDASWORD"
>bttv</I
> driver applications should set the
<CODE
CLASS="CONSTANT"
>V4L2_FBUF_FLAG_OVERLAY</CODE
> flag.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_FLAG_CHROMAKEY</CODE
></TD
><TD
>0x0004</TD
><TD
>Use chroma-keying. The chroma-key color is
determined by the <CODE
CLASS="STRUCTFIELD"
>chromakey</CODE
> field of
struct&nbsp;<A
HREF="x6570.htm#V4L2-WINDOW"
>v4l2_window</A
> and negotiated with the <A
HREF="r10944.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_S_FMT</CODE
></A
> ioctl, see <A
HREF="x6570.htm"
>Section 4.2</A
>
and
            <A
HREF="x6909.htm"
>Section 4.4</A
>.</TD
></TR
><TR
><TD
COLSPAN="3"
>There are no flags to enable
clipping using a list of clip rectangles or a bitmap. These methods
are negotiated with the <A
HREF="r10944.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_S_FMT</CODE
></A
> ioctl, see <A
HREF="x6570.htm"
>Section 4.2</A
> and <A
HREF="x6909.htm"
>Section 4.4</A
>.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_FLAG_LOCAL_ALPHA</CODE
></TD
><TD
>0x0008</TD
><TD
>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.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_FLAG_GLOBAL_ALPHA</CODE
></TD
><TD
>0x0010</TD
><TD
>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 <CODE
CLASS="STRUCTFIELD"
>global_alpha</CODE
> field of
struct&nbsp;<A
HREF="x6570.htm#V4L2-WINDOW"
>v4l2_window</A
> and negotiated with the <A
HREF="r10944.htm"
><CODE
CLASS="CONSTANT"
>VIDIOC_S_FMT</CODE
></A
> ioctl, see <A
HREF="x6570.htm"
>Section 4.2</A
>
and <A
HREF="x6909.htm"
>Section 4.4</A
>.</TD
></TR
><TR
><TD
><CODE
CLASS="CONSTANT"
>V4L2_FBUF_FLAG_LOCAL_INV_ALPHA</CODE
></TD
><TD
>0x0020</TD
><TD
>Like
<CODE
CLASS="CONSTANT"
>V4L2_FBUF_FLAG_LOCAL_ALPHA</CODE
>, 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.</TD
></TR
></TBODY
></TABLE
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN10920"
></A
><H2
>Return Value</H2
><P
>On success <SPAN
CLASS="RETURNVALUE"
>0</SPAN
> is returned, on error <SPAN
CLASS="RETURNVALUE"
>-1</SPAN
> and the <CODE
CLASS="VARNAME"
>errno</CODE
> variable is set appropriately:</P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><SPAN
CLASS="ERRORCODE"
>EPERM</SPAN
></DT
><DD
><P
><CODE
CLASS="CONSTANT"
>VIDIOC_S_FBUF</CODE
> can only be called
by a privileged user to negotiate the parameters for a destructive
overlay.</P
></DD
><DT
><SPAN
CLASS="ERRORCODE"
>EBUSY</SPAN
></DT
><DD
><P
>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.</P
></DD
><DT
><SPAN
CLASS="ERRORCODE"
>EINVAL</SPAN
></DT
><DD
><P
>The ioctl is not supported or the
<CODE
CLASS="CONSTANT"
>VIDIOC_S_FBUF</CODE
> parameters are unsuitable.</P
></DD
></DL
></DIV
></DIV
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ALIGN="center"
VALIGN="top"
><A
HREF="book1.htm"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="r10944.htm"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
VIDIOC_TRY_EXT_CTRLS</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="r7624.htm"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>ioctl VIDIOC_G_FMT, VIDIOC_S_FMT,
VIDIOC_TRY_FMT</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>