video: make OSD/subtitle bitmaps refcounted (sort of)

Making OSD/subtitle bitmaps refcounted was planend a longer time ago,
e.g. the sub_bitmaps.packed field (which refcounts the subtitle bitmap
data) was added in 2016. But nothing benefited much from it, because
struct sub_bitmaps was usually stack allocated, and there was this weird
callback stuff through osd_draw().

Make it possible to get actually refcounted subtitle bitmaps on the OSD
API level. For this, we just copy all subtitle data other than the
bitmaps with sub_bitmaps_copy(). At first, I had planned some fancy
refcount shit, but when that was a big mess and hard to debug and just
boiled to emulating malloc(), I made it a full allocation+copy. This
affects mostly the parts array. With crazy ASS subtitles, this parts
array can get pretty big (thousands of elements or more), in which case
the extra alloc/copy could become performance relevant. But then again
this is just pure bullshit, and I see no need to care. In practice, this
extra work most likely gets drowned out by libass murdering a single
core (while mpv is waiting for it) anyway. So fuck it.

I just wanted this so draw_bmp.c requires only a single call to render
everything. VOs also can benefit from this, because the weird callback
shit isn't necessary anymore (simpler code), but I haven't done anything
about it yet. In general I'd hope this will work towards simplifying the
OSD layer, which is prerequisite for making actual further improvements.

I haven't tested some cases such as the "overlay-add" command. Maybe it
crashes now? Who knows, who cares.

In addition, it might be worthwhile to reduce the code duplication
between all the things that output subtitle bitmaps (with repacking,
image allocation, etc.), but that's orthogonal.

1 files changed, 12 insertions, 10 deletions

diff --git a/sub/sd_ass.c b/sub/sd_ass.c
index 40e5093d8e..d51f892dd4 100644
--- a/sub/sd_ass.c
+++ b/sub/sd_ass.c
@@ -50,7 +50,7 @@ struct sd_ass_priv {
     bool clear_once;
     bool on_top;
     struct mp_ass_packer *packer;
-    struct sub_bitmap *bs;
+    struct sub_bitmap_copy_cache *copy_cache;
     char last_text[500];
     struct mp_image_params video_params;
     struct mp_image_params last_params;
@@ -498,8 +498,8 @@ static long long find_timestamp(struct sd *sd, double pts)
 
 #undef END
 
-static void get_bitmaps(struct sd *sd, struct mp_osd_res dim, int format,
-                        double pts, struct sub_bitmaps *res)
+static struct sub_bitmaps *get_bitmaps(struct sd *sd, struct mp_osd_res dim,
+                                       int format, double pts)
 {
     struct sd_ass_priv *ctx = sd->priv;
     struct mp_subtitle_opts *opts = sd->opts;
@@ -508,9 +508,10 @@ static void get_bitmaps(struct sd *sd, struct mp_osd_res dim, int format,
     bool converted = ctx->is_converted || no_ass;
     ASS_Track *track = no_ass ? ctx->shadow_track : ctx->ass_track;
     ASS_Renderer *renderer = ctx->ass_renderer;
+    struct sub_bitmaps *res = &(struct sub_bitmaps){0};
 
     if (pts == MP_NOPTS_VALUE || !renderer)
-        return;
+        goto done;
 
     double scale = dim.display_par;
     if (!converted && (!opts->ass_style_override ||
@@ -544,14 +545,14 @@ static void get_bitmaps(struct sd *sd, struct mp_osd_res dim, int format,
     ASS_Image *imgs = ass_render_frame(renderer, track, ts, &changed);
     mp_ass_packer_pack(ctx->packer, &imgs, 1, changed, format, res);
 
-    if (!converted && res->num_parts > 0) {
-        // mangle_colors() modifies the color field, so copy the thing.
-        MP_TARRAY_GROW(ctx, ctx->bs, res->num_parts);
-        memcpy(ctx->bs, res->parts, sizeof(ctx->bs[0]) * res->num_parts);
-        res->parts = ctx->bs;
+done:
+    // mangle_colors() modifies the color field, so copy the thing _before_.
+    res = sub_bitmaps_copy(&ctx->copy_cache, res);
 
+    if (!converted && res)
         mangle_colors(sd, res);
-    }
+
+    return res;
 }
 
 struct buf {
@@ -752,6 +753,7 @@ static void uninit(struct sd *sd)
     ass_free_track(ctx->shadow_track);
     enable_output(sd, false);
     ass_library_done(ctx->ass_library);
+    talloc_free(ctx->copy_cache);
 }
 
 static int control(struct sd *sd, enum sd_ctrl cmd, void *arg)