osd_libass: fix displaying empty text, fix API usage

If empty text is rendered, the bounding box is empty. Instead of
continuing with a bogus bounding box that would result in garbage
being rendered on screen, make the OSD image invisible.

This happened when playing demuxer SRT subtitles (e.g. SRT embedded in
MKV) with -no-ass at the moment a subtitle line disappeared.

Unrelated to this issue, fix libass API usage. Delete the event with
libass_flush_events(), instead of trying to reuse the previous event.

Based on a patch by uau.

1 files changed, 6 insertions, 11 deletions

diff --git a/sub/osd_libass.c b/sub/osd_libass.c
index 3e6c9a872a..9f15173442 100644
--- a/sub/osd_libass.c
+++ b/sub/osd_libass.c
@@ -149,7 +149,10 @@ static void draw_ass_osd(struct osd_state *osd, mp_osd_obj_t *obj)
                                        NULL);
 
     int x1, y1, x2, y2;
-    ass_bb(imgs, &x1, &y1, &x2, &y2);
+    if (!ass_bb(imgs, &x1, &y1, &x2, &y2)) {
+        obj->flags &= ~OSDFLAG_VISIBLE;
+        return;
+    }
 
     obj->bbox.x1 = x1;
     obj->bbox.y1 = y1;
@@ -200,22 +203,14 @@ static ASS_Track *create_osd_ass_track(struct osd_state *osd)
     return track;
 }
 
-// xxx extremely evil hack to get rid of '[ass] Event height has changed'
-static void reset_ass_event(ASS_Event *event)
-{
-    free(event->render_priv);
-    event->render_priv = NULL;
-}
-
 static ASS_Event *get_osd_ass_event(ASS_Track *track)
 {
-    if (!track->n_events)
-        ass_alloc_event(track);
+    ass_flush_events(track);
+    ass_alloc_event(track);
     ASS_Event *event = track->events + 0;
     event->Start = 0;
     event->Duration = 100;
     event->Style = track->default_style;
-    reset_ass_event(event);
     return event;
 }