player/sub: avoid wasteful subtitle redraws

This only affects two special cases: printing subtitles to the terminal
and printing subtitles on a still picture. Previously, mpv was very dumb
here and spammed this logic on every single loop. For terminal
subtitles, this isn't as big of a deal, but for the image case this is
pretty bad. The entire VO constantly redrew even when there was no need
to which can be very expensive depending on user settings.

Instead, let's rework sub_read_packets so that it also tells us whether
or not the subtitle packets update in some way in addition to telling us
whether or not to read more. Since we cache all packets thanks to the
previous commit, we can leverage this information to make a guess
whether or not the current subtitle packet is supposed to be visible on
the screen. Because the redraw now only happens when it is needed, the
mp_set_timeout_hack can be removed.

1 files changed, 4 insertions, 0 deletions

diff --git a/player/core.h b/player/core.h
index 8a49585cdf..9d9c4e8307 100644
--- a/player/core.h
+++ b/player/core.h
@@ -402,6 +402,9 @@ typedef struct MPContext {
     int last_chapter_seek;
     bool last_chapter_flag;
 
+    /* Heuristic for potentially redrawing subs. */
+    bool redraw_subs;
+
     bool paused;            // internal pause state
     bool playback_active;   // not paused, restarting, loading, unloading
     bool in_playloop;
@@ -621,6 +624,7 @@ void mp_load_builtin_scripts(struct MPContext *mpctx);
 int64_t mp_load_user_script(struct MPContext *mpctx, const char *fname);
 
 // sub.c
+void redraw_subs(struct MPContext *mpctx);
 void reset_subtitle_state(struct MPContext *mpctx);
 void reinit_sub(struct MPContext *mpctx, struct track *track);
 void reinit_sub_all(struct MPContext *mpctx);