mirror of https://gitee.com/openkylin/linux.git
464 lines
18 KiB
XML
464 lines
18 KiB
XML
<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. 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>
|