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

[Stefano Sabatini]

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;
+    } 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 },
-- 
1.7.9.5