[FFmpeg-devel] [PATCH] lavfi: Add support to process_command in vf_eq.c

[Stefano Sabatini]

On date Tuesday 2015-03-10 00:27:52 +0530, Arwa Arif encoded:
> On Fri, Feb 20, 2015 at 5:41 AM, Stefano Sabatini <stefasab at gmail.com>
> wrote:
> 
> > On date Thursday 2015-02-19 17:13:15 +0530, Arwa Arif encoded:
> > > Updated the patch.
> >
> > > From 66a8c9d03995c9e7c6ccc05fb9b20756f51c17f4 Mon Sep 17 00:00:00 2001
> > > From: Arwa Arif <arwaarif1994 at gmail.com>
> > > Date: Thu, 19 Feb 2015 01:26:44 +0530
> > > Subject: [PATCH] Add process_command to eq.
> > >
> > > ---
> > >  doc/filters.texi    |   35 +++++++++++
> > >  libavfilter/vf_eq.c |  171
> > +++++++++++++++++++++++++++++++++++++--------------
> > >  libavfilter/vf_eq.h |   56 +++++++++++++++--
> > >  3 files changed, 210 insertions(+), 52 deletions(-)
> > >
> > > diff --git a/doc/filters.texi b/doc/filters.texi
> > > index 191b52f..e5bf3a2 100644
> > > --- a/doc/filters.texi
> > > +++ b/doc/filters.texi
> > > @@ -4402,6 +4402,41 @@ Default is @code{1.0}.
> > >
> > >  @end table
> > >
> > > + at subsection Commands
> > > +The filter supports the following commands:
> > > +
> > > + at table @option
> > > + at item contrast
> > > +Set the contrast expression.
> > > +
> > > + at item brightness
> > > +Set the brightness expression.
> > > +
> > > + at item saturation
> > > +Set the saturation expression.
> > > +
> > > + at item gamma
> > > +Set the gamma expression.
> > > +
> > > + at item gamma_r
> > > +Set the gamma_r expression.
> > > +
> > > + at item gamma_g
> > > +Set gamma_g expression.
> > > +
> > > + at item gamma_b
> > > +Set gamma_b expression.
> > > +
> > > + at item gamma_weight
> > > +Set gamma_weight expression.
> > > +
> > > +The command accepts the same syntax of the corresponding option.
> >
> > What parameters do the expressions accept? Can you suggest some useful
> > use-case? (And add useful examples in the docs?)
> >
> >

> There are no parameters accepted by the expressions. I will add some
> examples in the doc.

Look how it is done in hue. In general an expression is useful if you
want to express something in function of the time or the number of
frame or something else.

[...]
> > > +    if (!strcmp(cmd, "contrast")) {
> > > +        ret = set_expr(&eq->contrast_pexpr, args, cmd, ctx);
> > > +        set_contrast(eq);
> > > +        return ret;
> > > +    }
> > > +    else if (!strcmp(cmd, "brightness")) {
> > > +        ret = set_expr(&eq->brightness_pexpr, args, cmd, ctx);
> > > +        set_brightness(eq);
> > > +        return ret;
> > > +    }
> > > +    else if (!strcmp(cmd, "saturation")) {
> > > +        ret = set_expr(&eq->saturation_pexpr, args, cmd, ctx);
> > > +        set_saturation(eq);
> > > +        return ret;
> > > +    }
> > > +    else if (!strcmp(cmd, "gamma")) {
> > > +        ret = set_expr(&eq->gamma_pexpr, args, cmd, ctx);
> > > +        set_gamma(eq);
> > > +        return ret;
> > > +    }
> > > +    else if (!strcmp(cmd, "gamma_r")) {
> > > +        ret = set_expr(&eq->gamma_r_pexpr, args, cmd, ctx);
> > > +        set_gamma(eq);
> > > +        return ret;
> > > +    }
> > > +    else if (!strcmp(cmd, "gamma_g")) {
> > > +        ret = set_expr(&eq->gamma_g_pexpr, args, cmd, ctx);
> > > +        set_gamma(eq);
> > > +        return ret;
> > > +    }
> > > +    else if (!strcmp(cmd, "gamma_b")) {
> > > +        ret = set_expr(&eq->gamma_b_pexpr, args, cmd, ctx);
> > > +        set_gamma(eq);
> > > +        return ret;
> > > +    }
> > > +    else if (!strcmp(cmd, "gamma_weight")) {
> > > +        ret = set_expr(&eq->gamma_weight_pexpr, args, cmd, ctx);
> > > +        set_gamma(eq);
> > > +        return ret;
> >
> > this can be probably factorized using a macro
> >
> >

> Okay. I was going through other filters which use macros, can you explain
> me the what is meant by the symbol ## in statement no.2 of the following
> code snippet:

## is the concatenation operator. See for example:
https://gcc.gnu.org/onlinedocs/cpp/Concatenation.html

> #define SET_SIZE_EXPR(name, opt_name) do {
>         \
>     ret = av_expr_parse_and_eval(&res, expr = rot->name##_expr_str,
>        \
>                                  var_names, rot->var_values,
>         \
>                                  func1_names, func1, NULL, NULL, rot, 0,
> ctx);     \
>     if (ret < 0 || isnan(res) || isinf(res) || res <= 0) {
>         \
>         av_log(ctx, AV_LOG_ERROR,
>        \
>                "Error parsing or evaluating expression for option %s: "
>        \
>                "invalid expression '%s' or non-positive or indefinite value
> %f\n", \
>                opt_name, expr, res);
>         \
>         return ret;
>        \
>     }

Something like:

#define SET_PARAM(param_name) \
   if (!strcmp(cmd, param_name)) { \
       ret = set_expr(&eq->param_name##_pexpr, args, cmd, ctx); \
       set_##param_name(eq); \
       return ret; \
   }

SET_PARAM(contrast);
SET_PARAM(brightness);
...

should probably work.

[...]
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