[FFmpeg-devel] [PATCH] swscale: Make sws_alloc_set_opts() public

[Ronald S. Bultje]

Hi,

On Sat, Aug 8, 2015 at 12:58 PM, Paul B Mahol <onemda at gmail.com> wrote:

> On 8/8/15, wm4 <nfxjfg at googlemail.com> wrote:
> > On Sat, 8 Aug 2015 18:17:37 +0200
> > Michael Niedermayer <michael at niedermayer.cc> wrote:
> >
> >> On Sat, Aug 08, 2015 at 05:58:29PM +0200, wm4 wrote:
> >> > On Sat,  8 Aug 2015 17:14:58 +0200
> >> > Michael Niedermayer <michaelni at gmx.at> wrote:
> >> >
> >> > > From: Michael Niedermayer <michael at niedermayer.cc>
> >> > >
> >> > > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> >> > > ---
> >> > >  libswscale/swscale.h          |   11 +++++++++++
> >> > >  libswscale/swscale_internal.h |   11 -----------
> >> > >  libswscale/version.h          |    4 ++--
> >> > >  3 files changed, 13 insertions(+), 13 deletions(-)
> >> > >
> >> > > diff --git a/libswscale/swscale.h b/libswscale/swscale.h
> >> > > index 903e120..055c9fc 100644
> >> > > --- a/libswscale/swscale.h
> >> > > +++ b/libswscale/swscale.h
> >> > > @@ -161,6 +161,17 @@ int sws_isSupportedEndiannessConversion(enum
> >> > > AVPixelFormat pix_fmt);
> >> > >  struct SwsContext *sws_alloc_context(void);
> >> > >
> >> > >  /**
> >> > > + * Allocate and return an SwsContext.
> >> > > + * This is like sws_getContext() but does not perform the init
> step,
> >> > > allowing
> >> > > + * the user to set additional AVOptions.
> >> > > + *
> >> > > + * @see sws_getContext()
> >> > > + */
> >> > > +struct SwsContext *sws_alloc_set_opts(int srcW, int srcH, enum
> >> > > AVPixelFormat srcFormat,
> >> > > +                                      int dstW, int dstH, enum
> >> > > AVPixelFormat dstFormat,
> >> > > +                                      int flags, const double
> >> > > *param);
> >> > > +
> >> >
> >> > This looks excessively useless and un-nice to use.
> >>
> >> what do you suggest ?
> >>
> >> The function is intended to replace:
> >>
> >> context = sws_alloc_context()
> >> if (!context)
> >>     handle error
> >>
> >> ret0 = av_opt_set_int(context, "sws_flags",  flags, 0);
> >> ret1 = av_opt_set_int(context, "srcw",       srcW, 0);
> >> ret2 = av_opt_set_int(context, "srch",       srcH, 0);
> >> ret3 = av_opt_set_int(context, "dstw",       dstW, 0);
> >> ret4 = av_opt_set_int(context, "dsth",       dstH, 0);
> >> ret5 = av_opt_set_int(context, "src_format", srcFormat, 0);
> >> ret6 = av_opt_set_int(context, "dst_format", dstFormat, 0);
> >> ret7 = av_opt_set(context, "alphablend", "none", 0);
> >
> > This does look better to me than a function which has some required
> > parameters (and at least 1 optional one!), but not all parameters which
> > are reasonably needed for general pixfmt conversion. Where are the
> > input and output colorspaces and ranges set?
> >
> > The "param" parameter is the worst part if this proposed function. What
> > does it even mean? I don't know because I didn't read the
> > implementation.
> >
> >> if (ret0 <0)
> >>     handle error, free context, return ret0
> >> if (ret1 <0)
> >>     handle error, free context, return ret1
> >> if (ret2 <0)
> >>     handle error, free context, return ret2
> >> if (ret3 <0)
> >>     handle error, free context, return ret3
> >> if (ret4 <0)
> >>     handle error, free context, return ret4
> >> if (ret5 <0)
> >>     handle error, free context, return ret5
> >> if (ret6 <0)
> >>     handle error, free context, return ret6
> >> if (ret7 <0)
> >>     handle error, free context, return ret7
> >
> > Oh come on, why would you need to check av_opt_set calls for options
> > that are guaranteed to exist? The codebase has hundreds of such
> > "unchecked" calls.
> >
> > And even if you insist that's it's necessary, you wrote it in a way
> > that makes it look like such error handling is more code. E.g. you
> > could write:
> >
> > if ((ret = av_opt_set_int(...)) < 0) goto error;
> >
> > (Or even put all av_opt_set calls into one if condition; it's not like
> > the error code will be useful anyway.)
> >
> >> by this:
> >>
> >> context = sws_alloc_set_opts(srcW, srcH,  srcFormat, dstW, dstH,
> >> dstFormat, flags, NULL);
> >> if (!context)
> >>     handle error
> >>
> >> ret = av_opt_set(context, "alphablend", "none", 0);
> >>
> >> if (ret <0)
> >>     handle error, free context, return ret
> >>
> >> and that looks alot nicer to me,
> >> but if someone has a even better idea?
> >>
> >>
> >
> > There's my very old patch, which made libswscale transparently set the
> > parameters of an input AVFrame. This would actually be the simplest API.
>
> +1


More +1 from me. The current sws API is a bloody pain (the double param
joke is just one of several terrible examples).

Ronald