[FFmpeg-devel] [PATCH] swscale: Implement alphablendaway for planar 4:4:4 formats

[Michael Niedermayer]

On Thu, Aug 06, 2015 at 10:24:52PM -0400, Ronald S. Bultje wrote:
> Hi,
> 
> On Thu, Aug 6, 2015 at 4:27 PM, Michael Niedermayer <michaelni at gmx.at>
> wrote:
> 
> > From: Michael Niedermayer <michael at niedermayer.cc>
> >
> > Fixes Ticket4746
> >
> > TODO: implement packed formats and subsampled formats
> >
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > ---
> >  doc/scaler.texi               |   13 ++++++
> >  libswscale/Makefile           |    3 +-
> >  libswscale/alphablend.c       |   55 +++++++++++++++++++++++
> >  libswscale/options.c          |    3 ++
> >  libswscale/swscale_internal.h |   12 +++++
> >  libswscale/utils.c            |   97
> > +++++++++++++++++++++++++++++++++++++++++
> >  6 files changed, 182 insertions(+), 1 deletion(-)
> >  create mode 100644 libswscale/alphablend.c
> >
> > diff --git a/doc/scaler.texi b/doc/scaler.texi
> > index 23d6393..4c55334 100644
> > --- a/doc/scaler.texi
> > +++ b/doc/scaler.texi
> > @@ -122,6 +122,19 @@ a_dither).
> >
> >  @end table
> >
> > + at item alphablend
> > +Set the alpha blending to use when the input has alpha but the output
> > does not.
> > +Default value is @samp{black}.
> > +
> > + at table @samp
> > + at item black
> > +Blend onto black
> > +
> > + at item none
> > +No blending
> > +
> > + at end table
> > +
> >  @end table
> 
> 
> I must admit I'm not a fan of having just two values for something like
> this. It seems to me you want 2 options, "blendmode", being "none" or
> "background" (or a float/alpha between 1.0/0.0), and the actual background
> color (black, white, blue, r=a,g=b,c=d). "black" vs. "none" seems like a
> future compat nightmare. Is it that hard to implement a proper rgb/yuv
> value solution?

The color value convertion support is in drawutils which is in
libavfilter. also drawutils lacks support for >8bit formats
so to get arbitrary color support with a clean non duplicated
implementation it would require moving drawutils
or the color related code from it to libavutil and extending it to
support all pixel formats. Unless iam missing something

Also i wanted to implement support for a checkerboard background
(which some applications use as default and it shows what
is transparent much better than black would)

So i would suggest that we implement ATM a "none" + "solidcolor" or
"background" or what name is preferred
and ill add a black/white checkerboard mode later and once drawutils
exist in libavutil we can then easily add a "blendcolor" AVOption
to specify the exact color

If noone objects then ill work on that (except drawutils moving and
extending)

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Freedom in capitalist society always remains about the same as it was in
ancient Greek republics: Freedom for slave owners. -- Vladimir Lenin
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