Re: [FFmpeg-devel] [PATCH] lsws/swscale.h: introduce sws_get_gaussian_vec

[Stefano Sabatini <stefasab@gmail.com>]

On date Friday 2023-09-01 18:54:40 +0200, Michael Niedermayer wrote:
> On Thu, Aug 31, 2023 at 07:16:20PM +0200, Stefano Sabatini wrote:
[...]
> > +/**
> > + * Compute and return a normalized Gaussian vector.
> > + *
> > + * @param vecp: pointer where the computed vector is put in case of
> > + *        success
> > + * @param standard_deviation the standard deviation used to generate
> > + *        the Gaussian vector, must be a non-negative value
> > + * @param quality the quality of the generated Gaussian vector, must
> > + *        be a non-negative value. It affects the lenght of the generated
> > + *        vector. A value equal to 3 corresponds to high quality.
> > + * @param log_ctx a pointer to an arbitrary struct of which the first
> > + *        field is a pointer to an AVClass struct (used for av_log)
> > + *        used for logging, can be NULL
> > + *
> > + * @return a negative error code on error, non negative otherwise
> > + */
> > +int sws_get_gaussian_vec(SwsVector **vecp,
> > +                         double standard_deviation, double quality,
> > +                         void *log_ctx);
> 
> which of the two do you consider better?
> 
> First, here the central part we return is the vector
> 
> SwsVector *gaus_vec = sws_getGaussianVec(NULL, 1, 2);
> SwsVector *temp_vec = sws_ConvolveVec(NULL, in_vec, gaus_vec);
> sws_averageVec(temp_vec, temp_vec, in_vec);
> 
> av_free(gaus_vec);
> return temp_vec; // Error checking here happens by temp_vec being NULL in all cases of error
> 
> vs.
> 
> Second, here the central part we return is the error code
> 
> SwsVector *gaus_vec = NULL;
> SwsVector *temp_vec = NULL;
> int err = sws_getGaussianVec(&gaus_vec, 1, 2);
> if (err<0)
>     goto fail;
> 
> err = sws_ConvolveVec(&temp_vec, in_vec, gaus_vec);
> if (err<0)
>     goto fail;
> 
> err = sws_averageVec(&temp_vec, temp_vec, in_vec);
> if (err<0)
>     goto fail;

The latter pattern enables differentiation between error codes (ENOMEM
or EINVAL) and provides feedback in the log message. With the former
you only know if it fails, but you don't know why (relevant in case
e.g. we make the parameter tunable by a filter and we don't want to
add additional validation and logging at the filter level).
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