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[media] v4l2 spec: clarify usage of V4L2_FBUF_FLAG_OVERLAY

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Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
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Hans Verkuil 2011-11-22 08:59:34 -03:00 committed by Mauro Carvalho Chehab
parent 0cb64f02b8
commit 05834fcf58
1 changed files with 14 additions and 9 deletions
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23
Documentation/DocBook/media/v4l/vidioc-g-fbuf.xml
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@ -364,15 +364,20 @@ capability and it is cleared otherwise.</entry>
<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_OVERLAY</constant> was never quite clear.
Most drivers seem to ignore this flag. For compatibility with the
<wordasword>bttv</wordasword> driver applications should set the
<constant>V4L2_FBUF_FLAG_OVERLAY</constant> flag.</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>