lavfi/tile: make color of blank/unused area configurable

Signed-off-by: Paul B Mahol <onemda@gmail.com>

doc/filters.texi

@@ -7119,6 +7119,10 @@ Set the inner border thickness (i.e. the number of pixels between frames). For
 more advanced padding options (such as having different values for the edges),
 refer to the pad video filter.
 
+@item color
+Specify the color of the unused area, it can be the name of a color
+(case insensitive match) or a 0xRRGGBB[AA] sequence.
+The default value of @var{color} is "black".
 @end table
 
 @subsection Examples

libavfilter/vf_tile.c

@@ -41,6 +41,7 @@ typedef struct {
     FFDrawContext draw;
     FFDrawColor blank;
     AVFrame *out_ref;
+    uint8_t rgba_color[4];
 } TileContext;
 
 #define REASONABLE_SIZE 1024
@@ -57,6 +58,7 @@ static const AVOption tile_options[] = {
         AV_OPT_TYPE_INT, {.i64 = 0}, 0, 1024, FLAGS },
     { "padding", "set inner border thickness in pixels", OFFSET(padding),
         AV_OPT_TYPE_INT, {.i64 = 0}, 0, 1024, FLAGS },
+    { "color",   "set the color of the unused area", OFFSET(rgba_color), AV_OPT_TYPE_COLOR, {.str = "black"}, .flags = FLAGS },
     {NULL},
 };
 
@@ -113,8 +115,7 @@ static int config_props(AVFilterLink *outlink)
     outlink->frame_rate = av_mul_q(inlink->frame_rate,
                                    (AVRational){ 1, tile->nb_frames });
     ff_draw_init(&tile->draw, inlink->format, 0);
-    /* TODO make the color an option, or find an unified way of choosing it */
-    ff_draw_color(&tile->draw, &tile->blank, (uint8_t[]){ 0, 0, 0, -1 });
+    ff_draw_color(&tile->draw, &tile->blank, tile->rgba_color);
 
     outlink->flags |= FF_LINK_FLAG_REQUEST_LOOP;