Hi, On Thursday 24 November 2011 13:22:10 Hans Verkuil wrote: > On Thursday, November 24, 2011 13:06:09 Laurent Pinchart wrote: > > On Thursday 24 November 2011 12:49:00 Hans Verkuil wrote: > > > On Thursday, November 24, 2011 12:39:54 Sylwester Nawrocki wrote: > > > > On 11/24/2011 12:09 PM, Laurent Pinchart wrote: > > > > > 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 <s.nawrocki@xxxxxxxxxxx> > > > > >>> Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx> > > > > >>> --- > > > > >>> > > > > >>> 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 > > > > >>> ></e ntry > > > > >>> > > > > >>> > <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 ? > > > > I think we should make it explicit that this global alpha value is > > applied in addition to a possibly per-pixel alpha value (if available in > > the selected format). > > > > > Huh? How can this be used for formats without an alpha channel? > > > > If my understanding is correct, this control sets a global alpha value > > for the whole overlay. For instance, with V4L2_CID_COLOR_ALPHA set to > > 0.5, an overlay using a non-alpha format (such as YUYV), or an overlay > > using an alpha format with the alpha value set to 1 for every pixel, > > would be half transparent. > > > > In other words, the resulting alpha value is the product of the global > > alpha value and the per-pixel alpha value. Non-alpha formats have an > > implicit per- pixel alpha value equal to 1 for every pixel. > > Well, if that's the case, then we already have an API for that > (http://hverkuil.home.xs4all.nl/spec/media.html#v4l2-window, field > global_alpha). > > It was my understanding that this is used with a mem2mem device where you > just want to fill in the alpha channel to the desired value. It's not used > inside the device at all (that happens later in the pipeline). OK, now I understand. Maybe the documentation should describe this a bit more explicitly ? -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
