sub: add --sub-gray option to display image subs in grayscale

MPlayer/mplayer2 still show DVD subtitles in gray. Depending on who you
ask, this can be considered a bug or a feature. Include rendering in
gray as explicit feature, so the user can decide what is better.

This affects all indexed sub bitmaps entering the OSD rendering path.
Currently, this means all image subs are affected by this option, but
nothing else.

7 files changed, 51 insertions, 3 deletions

diff --git a/DOCS/man/en/changes.rst b/DOCS/man/en/changes.rst
index b46691c888..eeafd537a9 100644
--- a/DOCS/man/en/changes.rst
+++ b/DOCS/man/en/changes.rst
@@ -64,7 +64,7 @@ General changes for mplayer2 to mpv
   handle these use cases. For yuv4mpeg, for example, use:
   ``mpv input.mkv -o output.y4m --no-audio``.
 * Image subtitles (DVDs etc.) are rendered in color and use more correct
-  positioning
+  positioning (color can be disabled with ``--sub-gray``)
 * General code cleanups
 * Many more changes
 
diff --git a/DOCS/man/en/options.rst b/DOCS/man/en/options.rst
index f0d9ddb57b..15007e03fc 100644
--- a/DOCS/man/en/options.rst
+++ b/DOCS/man/en/options.rst
@@ -1889,6 +1889,12 @@
 
     *NOTE*: never applied to text subtitles.
 
+--sub-gray
+    Convert image subtitles to grayscale. Can help making yellow DVD/Vobsubs
+    look nicer.
+
+    *NOTE*: never affects text subtitles.
+
 --sub-pos=<0-100>
     Specify the position of subtitles on the screen. The value is the vertical
     position of the subtitle in % of the screen height.
diff --git a/core/cfg-mplayer.h b/core/cfg-mplayer.h
index ded7245f83..23b937f91a 100644
--- a/core/cfg-mplayer.h
+++ b/core/cfg-mplayer.h
@@ -507,6 +507,7 @@ const m_option_t common_opts[] = {
      M_CHOICES(({"exact", 0}, {"fuzzy", 1}, {"all", 2}))},
     {"sub-pos", &sub_pos, CONF_TYPE_INT, CONF_RANGE, 0, 100, NULL},
     OPT_FLOATRANGE("sub-gauss", sub_gauss, 0, 0.0, 3.0),
+    OPT_MAKE_FLAGS("sub-gray", sub_gray, 0),
     OPT_MAKE_FLAGS("ass", ass_enabled, 0),
     OPT_FLOATRANGE("sub-scale", sub_scale, 0, 0, 100),
     OPT_FLOATRANGE("ass-line-spacing", ass_line_spacing, 0, -1000, 1000),
diff --git a/core/options.h b/core/options.h
index 58d6a64e70..47f4593b9b 100644
--- a/core/options.h
+++ b/core/options.h
@@ -114,6 +114,7 @@ typedef struct MPOpts {
     struct osd_style_opts *osd_style;
     float sub_scale;
     float sub_gauss;
+    int sub_gray;
     int ass_enabled;
     float ass_line_spacing;
     int ass_top_margin;
diff --git a/sub/img_convert.c b/sub/img_convert.c
index 274a83d833..578a20b646 100644
--- a/sub/img_convert.c
+++ b/sub/img_convert.c
@@ -128,3 +128,38 @@ bool osd_conv_blur_rgba(struct osd_conv_cache *c, struct sub_bitmaps *imgs,
     }
     return true;
 }
+
+static void rgba_to_gray(uint32_t *colors, size_t count)
+{
+    for (int n = 0; n < count; n++) {
+        uint32_t c = colors[n];
+        int b = c & 0xFF;
+        int g = (c >> 8) & 0xFF;
+        int r = (c >> 16) & 0xFF;
+        int a = (c >> 24) & 0xFF;
+        r = g = b = (r + g + b) / 3;
+        colors[n] = b | (g << 8) | (r << 16) | (a << 24);
+    }
+}
+
+bool osd_conv_idx_to_gray(struct osd_conv_cache *c, struct sub_bitmaps *imgs)
+{
+    struct sub_bitmaps src = *imgs;
+    if (src.format != SUBBITMAP_INDEXED)
+        return false;
+
+    talloc_free(c->parts);
+    imgs->parts = c->parts = talloc_array(c, struct sub_bitmap, src.num_parts);
+
+    for (int n = 0; n < src.num_parts; n++) {
+        struct sub_bitmap *d = &imgs->parts[n];
+        struct sub_bitmap *s = &src.parts[n];
+        struct osd_bmp_indexed sb = *(struct osd_bmp_indexed *)s->bitmap;
+
+        rgba_to_gray(sb.palette, 256);
+
+        *d = *s;
+        d->bitmap = talloc_memdup(c->parts, &sb, sizeof(sb));
+    }
+    return true;
+}
diff --git a/sub/img_convert.h b/sub/img_convert.h
index eab543051c..2ea17ef889 100644
--- a/sub/img_convert.h
+++ b/sub/img_convert.h
@@ -11,7 +11,9 @@ struct osd_conv_cache *osd_conv_cache_new(void);
 // These functions convert from one OSD format to another. On success, they copy
 // the converted image data into c, and change imgs to point to the data.
 bool osd_conv_idx_to_rgba(struct osd_conv_cache *c, struct sub_bitmaps *imgs);
+// Sub postprocessing
 bool osd_conv_blur_rgba(struct osd_conv_cache *c, struct sub_bitmaps *imgs,
                         double gblur);
+bool osd_conv_idx_to_gray(struct osd_conv_cache *c, struct sub_bitmaps *imgs);
 
 #endif
diff --git a/sub/sub.c b/sub/sub.c
index 66ee6ea42c..0dae442aee 100644
--- a/sub/sub.c
+++ b/sub/sub.c
@@ -221,11 +221,14 @@ static void render_object(struct osd_state *osd, struct osd_object *obj,
 
     bool cached = false; // do we have a copy of all the image data?
 
+    if (out_imgs->format == SUBBITMAP_INDEXED && opts->sub_gray)
+        cached |= osd_conv_idx_to_gray(obj->cache[0], out_imgs);
+
     if (formats[SUBBITMAP_RGBA] && out_imgs->format == SUBBITMAP_INDEXED)
-        cached |= osd_conv_idx_to_rgba(obj->cache[0], out_imgs);
+        cached |= osd_conv_idx_to_rgba(obj->cache[1], out_imgs);
 
     if (out_imgs->format == SUBBITMAP_RGBA && opts->sub_gauss != 0.0f)
-        cached |= osd_conv_blur_rgba(obj->cache[1], out_imgs, opts->sub_gauss);
+        cached |= osd_conv_blur_rgba(obj->cache[2], out_imgs, opts->sub_gauss);
 
     if (cached)
         obj->cached = *out_imgs;