[FFmpeg-devel] [PATCH] lavfi/drawtext: add support to expansion of generic expressions

[Nicolas George]

Le septidi 7 frimaire, an CCXXI, Stefano Sabatini a écrit :
> TODO: bump micro
> ---
>  doc/filters.texi          |    8 ++++++++
>  libavfilter/vf_drawtext.c |   24 ++++++++++++++++++++++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/doc/filters.texi b/doc/filters.texi
> index 99654eb..5c8bc6f 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -2075,6 +2075,14 @@ The following functions are available:
>  
>  @table @command
>  
> + at item expr, e
> +The expression evaluation result.
> +It must take one argument specifying the expression to be evaluated,
> +which accepts the same constants and functions as the @var{x} and
> + at var{y} values. Note that not all constants should be used, for
> +example the text size is not known at this point, so the constants
> + at var{text_w} and @var{text_h} will have an undefined value.
> +
>  @item gmtime
>  The time at which the filter is running, expressed in UTC.
>  It can accept an argument: a strftime() format string.
> diff --git a/libavfilter/vf_drawtext.c b/libavfilter/vf_drawtext.c
> index 96512ab..cb23555 100644
> --- a/libavfilter/vf_drawtext.c
> +++ b/libavfilter/vf_drawtext.c
> @@ -167,6 +167,7 @@ typedef struct {
>      AVTimecode  tc;                 ///< timecode context
>      int tc24hmax;                   ///< 1 if timecode is wrapped to 24 hours, 0 otherwise
>      int frame_id;
> +    int expr_func_warning_done;
>  } DrawTextContext;
>  
>  #define OFFSET(x) offsetof(DrawTextContext, x)
> @@ -643,12 +644,35 @@ static int func_strftime(AVFilterContext *ctx, AVBPrint *bp,
>      return 0;
>  }
>  
> +static int func_eval_expr(AVFilterContext *ctx, AVBPrint *bp,
> +                          char *fct, unsigned argc, char **argv, int tag)
> +{
> +    DrawTextContext *dtext = ctx->priv;
> +    double res;
> +    int ret;
> +
> +    ret = av_expr_parse_and_eval(&res, argv[0], var_names, dtext->var_values,
> +                                 NULL, NULL, fun2_names, fun2,
> +                                 &dtext->prng, 0, ctx);
> +    if (ret < 0 && !dtext->expr_func_warning_done) {
> +        av_log(ctx, AV_LOG_WARNING,
> +               "Expression '%s' for the expr text expansion function is not valid\n",
> +               argv[0]);
> +        dtext->expr_func_warning_done = 1;

Any reason not just return an error? Most of the time, I rather dislike
programs that continue running when the user made a stupid typo that will
make their output useless.

> +    } else {
> +        av_bprintf(bp, "%f", res);
> +    }
> +    return ret;
> +}
> +
>  static const struct drawtext_function {
>      const char *name;
>      unsigned argc_min, argc_max;
>      int tag; /** opaque argument to func */
>      int (*func)(AVFilterContext *, AVBPrint *, char *, unsigned, char **, int);
>  } functions[] = {
> +    { "expr",      1, 1, 0,   func_eval_expr },
> +    { "e",         1, 1, 0,   func_eval_expr },
>      { "pts",       0, 0, 0,   func_pts      },
>      { "gmtime",    0, 1, 'G', func_strftime },
>      { "localtime", 0, 1, 'L', func_strftime },

Apart from the remark above, looks good, and a very good idea too, thanks.

Regards,

-- 
  Nicolas George
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