On Thursday, November 24, 2011 12:39:54 Sylwester Nawrocki wrote:
> Hi Laurent,
>
> On 11/24/2011 12:09 PM, Laurent Pinchart wrote:
> > Hi Sylwester and Hans,
> >
> > On Thursday 24 November 2011 12:00:45 Hans Verkuil wrote:
> >> On Thursday, November 24, 2011 11:53:16 Sylwester Nawrocki wrote:
> >>> This control is intended for video capture or memory-to-memory
> >>> devices that are capable of setting up the alpha conponent to
> >>> some arbitrary value.
> >>> The V4L2_CID_COLOR_ALPHA control allows to set the alpha channel
> >>> globally to a value in range from 0 to 255.
> >>>
> >>> Signed-off-by: Sylwester Nawrocki <[email protected]>
> >>> Signed-off-by: Kyungmin Park <[email protected]>
> >>> ---
> >>>
> >>> Documentation/DocBook/media/v4l/controls.xml | 20
> >>> ++++++++++++++------ .../DocBook/media/v4l/pixfmt-packed-rgb.xml
> >>> | 7 +++++-- drivers/media/video/v4l2-ctrls.c |
> >>> 7 +++++++ include/linux/videodev2.h | 6
> >>> +++--- 4 files changed, 29 insertions(+), 11 deletions(-)
> >>>
> >>> diff --git a/Documentation/DocBook/media/v4l/controls.xml
> >>> b/Documentation/DocBook/media/v4l/controls.xml index 3bc5ee8..7f99222
> >>> 100644
> >>> --- a/Documentation/DocBook/media/v4l/controls.xml
> >>> +++ b/Documentation/DocBook/media/v4l/controls.xml
> >>> @@ -324,12 +324,6 @@ minimum value disables backlight
> >>> compensation.</entry>
> >>>
> >>> (usually a microscope).</entry>
> >>>
> >>> </row>
> >>> <row>
> >>>
> >>> - <entry><constant>V4L2_CID_LASTP1</constant></entry>
> >>> - <entry></entry>
> >>> - <entry>End of the predefined control IDs (currently
> >>> -<constant>V4L2_CID_ILLUMINATORS_2</constant> + 1).</entry>
> >>> - </row>
> >>> - <row>
> >>>
> >>> <entry><constant>V4L2_CID_MIN_BUFFERS_FOR_CAPTURE</constant></entry
> >>> > <entry>integer</entry>
> >>> <entry>This is a read-only control that can be read by the
> >>> application
> >>>
> >>> @@ -345,6 +339,20 @@ and used as a hint to determine the number of OUTPUT
> >>> buffers to pass to REQBUFS.
> >>>
> >>> The value is the minimum number of OUTPUT buffers that is necessary for
> >>> hardware to work.</entry>
> >>>
> >>> </row>
> >>>
> >>> + <row id="v4l2-color-alpha">
> >>> + <entry><constant>V4L2_CID_COLOR_ALPHA</constant></entry>
> >>> + <entry>integer</entry>
> >>> + <entry> Sets the color alpha component on the capture device. It is
> >>> + applicable to any pixel formats that contain the alpha component,
> >>> + e.g. <link linkend="rgb-formats">packed RGB image formats</link>.
> >>> + </entry>
> >
> > As the alpha value is global, isn't it applicable to formats with no alpha
> > component as well ?
>
> Hmm, I can't say no.. The control was intended as a means of setting up
> the alpha value for packed RGB formats:
> http://linuxtv.org/downloads/v4l-dvb-apis/packed-rgb.html#rgb-formats
>
> However it could well be used for formats with no alpha. Do you think
> the second sentence above should be removed or should something else be
> added to indicate it doesn't necessarily have to have a connection
> with ARGB color formats ?
Huh? How can this be used for formats without an alpha channel?
>
> >
> >>> + </row>
> >>> + <row>
> >>> + <entry><constant>V4L2_CID_LASTP1</constant></entry>
> >>> + <entry></entry>
> >>> + <entry>End of the predefined control IDs (currently
> >>> + <constant>V4L2_CID_COLOR_ALPHA</constant> + 1).</entry>
> >>> + </row>
> >>>
> >>> <row>
> >>>
> >>> <entry><constant>V4L2_CID_PRIVATE_BASE</constant></entry>
> >>> <entry></entry>
> >>>
> >>> diff --git a/Documentation/DocBook/media/v4l/pixfmt-packed-rgb.xml
> >>> b/Documentation/DocBook/media/v4l/pixfmt-packed-rgb.xml index
> >>> 4db272b..da4c360 100644
> >>> --- a/Documentation/DocBook/media/v4l/pixfmt-packed-rgb.xml
> >>> +++ b/Documentation/DocBook/media/v4l/pixfmt-packed-rgb.xml
> >>> @@ -428,8 +428,11 @@ colorspace
> >>> <constant>V4L2_COLORSPACE_SRGB</constant>.</para>
> >>>
> >>> <para>Bit 7 is the most significant bit. The value of a = alpha
> >>>
> >>> bits is undefined when reading from the driver, ignored when writing
> >>> to the driver, except when alpha blending has been negotiated for a
> >>>
> >>> -<link linkend="overlay">Video Overlay</link> or <link
> >>> -linkend="osd">Video Output Overlay</link>.</para>
> >>> +<link linkend="overlay">Video Overlay</link> or <link linkend="osd">
> >>> +Video Output Overlay</link> or when global alpha has been configured
> >>> +for a <link linkend="capture">Video Capture</link> by means of
> >>> +<link linkend="v4l2-color-alpha"> <constant>V4L2_CID_COLOR_ALPHA
> >>> +</constant> </link> control.</para>
> >>>
> >>> <example>
> >>>
> >>> <title><constant>V4L2_PIX_FMT_BGR24</constant> 4 × 4 pixel
> >>>
> >>> diff --git a/drivers/media/video/v4l2-ctrls.c
> >>> b/drivers/media/video/v4l2-ctrls.c index 5552f81..bd90955 100644
> >>> --- a/drivers/media/video/v4l2-ctrls.c
> >>> +++ b/drivers/media/video/v4l2-ctrls.c
> >>> @@ -466,6 +466,7 @@ const char *v4l2_ctrl_get_name(u32 id)
> >>>
> >>> case V4L2_CID_ILLUMINATORS_2: return "Illuminator 2";
> >>> case V4L2_CID_MIN_BUFFERS_FOR_CAPTURE: return "Minimum Number of
> >>> Capture Buffers"; case V4L2_CID_MIN_BUFFERS_FOR_OUTPUT: return
> >>> "Minimum Number of Output Buffers";
> >>>
> >>> + case V4L2_CID_COLOR_ALPHA: return "Color Alpha";
> >>
> >> I prefer CID_ALPHA_COLOR and string "Alpha Color". I think it is more
> >> natural than the other way around.
>
> OK, I guess you're right. And Google returns about twice as many hits for
> "alpha color" than for "color alpha"...
>
> >
> > I'm not too found of "color" in the name. Is the alpha value considered as
> > a
> > color ?
>
> Certainly it isn't, but Alpha alone looks a bit odd. It's too generic IMHO.
How about V4L2_CID_ALPHA_COMPONENT?
Regards,
Hans
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