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

[Paul B Mahol]

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