[FFmpeg-devel] avfilter/vf_overlay: add show property/command

diff --git a/doc/filters.texi b/doc/filters.texi
index bd93e0a..f9b623c 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -11615,11 +11615,16 @@  on the main video. Default value is "0" for both expressions. In case
 the expression is invalid, it is set to a huge value (meaning that the
 overlay will not be displayed within the output visible area).
 
+@item show
+Set the expression for controlling to show or hide the overlaid video.
+Default value is "1". Expression evaluating to 0 means to hide,
+any other value means to show. Internally the result normalized to 0 or 1.
+
 @item eof_action
 See @ref{framesync}.
 
 @item eval
-Set when the expressions for @option{x}, and @option{y} are evaluated.
+Set when the expressions for @option{x}, @option{y} and @option{show} are evaluated.
 
 It accepts the following values:
 @table @samp
@@ -11670,7 +11675,7 @@  Set format of alpha of the overlaid video, it can be @var{straight} or
 @var{premultiplied}. Default is @var{straight}.
 @end table
 
-The @option{x}, and @option{y} expressions can contain the following
+The @option{x}, @option{y} and @option{show} expressions can contain the following
 parameters.
 
 @table @option
@@ -11702,6 +11707,9 @@  the position in the file of the input frame, NAN if unknown
 @item t
 The timestamp, expressed in seconds. It's NAN if the input timestamp is unknown.
 
+@item show
+the computed value of @var{show} normalized to 0 or 1 according to wether overlaid video shown or hidden.
+
 @end table
 
 This filter also supports the @ref{framesync} options.
@@ -11730,6 +11738,10 @@  The command accepts the same syntax of the corresponding option.
 
 If the specified expression is not valid, it is kept at its current
 value.
+
+@item show
+Modify the expression to show or to hide the overlaid video.
+
 @end table
 
 @subsection Examples
diff --git a/libavfilter/vf_overlay.c b/libavfilter/vf_overlay.c
index c6a6ac8..891db9e 100644
--- a/libavfilter/vf_overlay.c
+++ b/libavfilter/vf_overlay.c
@@ -52,6 +52,7 @@  static const char *const var_names[] = {
     "n",            ///< number of frame
     "pos",          ///< position in the file
     "t",            ///< timestamp expressed in seconds
+    "show",         ///< show/hide overlay
     NULL
 };
 
@@ -67,6 +68,7 @@  enum var_name {
     VAR_N,
     VAR_POS,
     VAR_T,
+    VAR_SHOW,
     VAR_VARS_NB
 };
 
@@ -111,6 +113,7 @@  typedef struct OverlayContext {
     int format;                 ///< OverlayFormat
     int alpha_format;
     int eval_mode;              ///< EvalMode
+    int show;                   ///< show or hide overlay
 
     FFFrameSync fs;
 
@@ -120,9 +123,9 @@  typedef struct OverlayContext {
     const AVPixFmtDescriptor *main_desc; ///< format descriptor for main input
 
     double var_values[VAR_VARS_NB];
-    char *x_expr, *y_expr;
+    char *x_expr, *y_expr, *show_expr;
 
-    AVExpr *x_pexpr, *y_pexpr;
+    AVExpr *x_pexpr, *y_pexpr, *show_pexpr;
 
     void (*blend_image)(AVFilterContext *ctx, AVFrame *dst, const AVFrame *src, int x, int y);
 } OverlayContext;
@@ -134,6 +137,7 @@  static av_cold void uninit(AVFilterContext *ctx)
     ff_framesync_uninit(&s->fs);
     av_expr_free(s->x_pexpr); s->x_pexpr = NULL;
     av_expr_free(s->y_pexpr); s->y_pexpr = NULL;
+    av_expr_free(s->show_pexpr); s->show_pexpr = NULL;
 }
 
 static inline int normalize_xy(double d, int chroma_sub)
@@ -153,6 +157,8 @@  static void eval_expr(AVFilterContext *ctx)
     s->var_values[VAR_X] = av_expr_eval(s->x_pexpr, s->var_values, NULL);
     s->x = normalize_xy(s->var_values[VAR_X], s->hsub);
     s->y = normalize_xy(s->var_values[VAR_Y], s->vsub);
+    s->var_values[VAR_SHOW] = av_expr_eval(s->show_pexpr, s->var_values, NULL);
+    s->show = s->var_values[VAR_SHOW]?1:0; // normalizing to fix value set
 }
 
 static int set_expr(AVExpr **pexpr, const char *expr, const char *option, void *log_ctx)
@@ -186,6 +192,8 @@  static int process_command(AVFilterContext *ctx, const char *cmd, const char *ar
         ret = set_expr(&s->x_pexpr, args, cmd, ctx);
     else if (!strcmp(cmd, "y"))
         ret = set_expr(&s->y_pexpr, args, cmd, ctx);
+    else if (!strcmp(cmd, "show"))
+        ret = set_expr(&s->show_pexpr, args, cmd, ctx);
     else
         ret = AVERROR(ENOSYS);
 
@@ -194,9 +202,11 @@  static int process_command(AVFilterContext *ctx, const char *cmd, const char *ar
 
     if (s->eval_mode == EVAL_MODE_INIT) {
         eval_expr(ctx);
-        av_log(ctx, AV_LOG_VERBOSE, "x:%f xi:%d y:%f yi:%d\n",
+        av_log(ctx, AV_LOG_VERBOSE, "x:%f xi:%d y:%f yi:%d show:%f showi:%d\n",
                s->var_values[VAR_X], s->x,
-               s->var_values[VAR_Y], s->y);
+               s->var_values[VAR_Y], s->y,
+               s->var_values[VAR_SHOW], s->show
+               );
     }
     return ret;
 }
@@ -348,9 +358,11 @@  static int config_input_overlay(AVFilterLink *inlink)
     s->var_values[VAR_N]     = 0;
     s->var_values[VAR_T]     = NAN;
     s->var_values[VAR_POS]   = NAN;
+    s->var_values[VAR_SHOW] = NAN;
 
     if ((ret = set_expr(&s->x_pexpr,      s->x_expr,      "x",      ctx)) < 0 ||
-        (ret = set_expr(&s->y_pexpr,      s->y_expr,      "y",      ctx)) < 0)
+        (ret = set_expr(&s->y_pexpr,      s->y_expr,      "y",      ctx)) < 0 ||
+        (ret = set_expr(&s->show_pexpr,   s->show_expr,   "show",   ctx)) < 0)
         return ret;
 
     s->overlay_is_packed_rgb =
@@ -359,9 +371,10 @@  static int config_input_overlay(AVFilterLink *inlink)
 
     if (s->eval_mode == EVAL_MODE_INIT) {
         eval_expr(ctx);
-        av_log(ctx, AV_LOG_VERBOSE, "x:%f xi:%d y:%f yi:%d\n",
+        av_log(ctx, AV_LOG_VERBOSE, "x:%f xi:%d y:%f yi:%d show:%f showi:%d\n",
                s->var_values[VAR_X], s->x,
-               s->var_values[VAR_Y], s->y);
+               s->var_values[VAR_Y], s->y,
+               s->var_values[VAR_SHOW], s->show);
     }
 
     av_log(ctx, AV_LOG_VERBOSE,
@@ -898,14 +911,15 @@  static int do_blend(FFFrameSync *fs)
         s->var_values[VAR_MAIN_H   ] = s->var_values[VAR_MH] = mainpic->height;
 
         eval_expr(ctx);
-        av_log(ctx, AV_LOG_DEBUG, "n:%f t:%f pos:%f x:%f xi:%d y:%f yi:%d\n",
+        av_log(ctx, AV_LOG_DEBUG, "n:%f t:%f pos:%f x:%f xi:%d y:%f yi:%d show:%f showi:%d\n",
                s->var_values[VAR_N], s->var_values[VAR_T], s->var_values[VAR_POS],
                s->var_values[VAR_X], s->x,
-               s->var_values[VAR_Y], s->y);
+               s->var_values[VAR_Y], s->y,
+               s->var_values[VAR_SHOW], s->show);
     }
 
-    if (s->x < mainpic->width  && s->x + second->width  >= 0 ||
-        s->y < mainpic->height && s->y + second->height >= 0)
+    if ((s->x < mainpic->width  && s->x + second->width  >= 0 ||
+        s->y < mainpic->height && s->y + second->height >= 0) && s->show)
         s->blend_image(ctx, mainpic, second, s->x, s->y);
     return ff_filter_frame(ctx->outputs[0], mainpic);
 }
@@ -951,6 +965,7 @@  static const AVOption overlay_options[] = {
     { "alpha", "alpha format", OFFSET(alpha_format), AV_OPT_TYPE_INT, {.i64=0}, 0, 1, FLAGS, "alpha_format" },
         { "straight",      "", 0, AV_OPT_TYPE_CONST, {.i64=0}, .flags = FLAGS, .unit = "alpha_format" },
         { "premultiplied", "", 0, AV_OPT_TYPE_CONST, {.i64=1}, .flags = FLAGS, .unit = "alpha_format" },
+    { "show", "set the show/hide overlay expression", OFFSET(show_expr), AV_OPT_TYPE_STRING, {.str = "1"}, CHAR_MIN, CHAR_MAX, FLAGS },
     { NULL }
 };