Add events garbage collection system and API.

libass/Makefile_library.am

@@ -1,6 +1,6 @@
-LIBASS_LT_CURRENT = 12
-LIBASS_LT_REVISION = 1
-LIBASS_LT_AGE = 3
+LIBASS_LT_CURRENT = 13
+LIBASS_LT_REVISION = 0
+LIBASS_LT_AGE = 4
 
 .asm.lo:
 	$(nasm_verbose)$(LIBTOOL) $(AM_V_lt) --tag=CC --mode=compile $(top_srcdir)/ltnasm.sh $(AS) $(ASFLAGS) -I$(top_srcdir)/libass/ -Dprivate_prefix=ass -o $@ $<

libass/ass.c

@@ -190,14 +190,29 @@ static int test_and_set_read_order_bit(ASS_Track *track, int id)
 {
     if (resize_read_order_bitmap(track, id) < 0)
         return -1;
-    int index = id / 32;
-    uint32_t bit = 1u << (id % 32);
+    int index = id >> 5;
+    uint32_t bit = 1u << (id & 0x1F);
     if (track->parser_priv->read_order_bitmap[index] & bit)
         return 1;
     track->parser_priv->read_order_bitmap[index] |= bit;
     return 0;
 }
 
+static inline void clear_read_order_bit(ASS_Track *track, int id)
+{
+    int index = id >> 5;
+    if (index < track->parser_priv->read_order_elems) {
+        uint32_t mask = ~(1u << (id & 0x1F));
+        track->parser_priv->read_order_bitmap[index] &= mask;
+    }
+}
+
+static inline void update_prune_ts(ASS_Track *track, const long long ts)
+{
+    if (ts < track->parser_priv->prune_next_ts)
+        track->parser_priv->prune_next_ts = ts;
+}
+
 // ==============================================================================================
 
 /**
@@ -1015,8 +1030,10 @@ static int process_events_line(ASS_Track *track, char *str)
         event = track->events + eid;
 
         int ret = process_event_tail(track, event, str, 0);
-        if (!ret)
+        if (!ret) {
+            update_prune_ts(track, event->Start + event->Duration);
             return 0;
+        }
         // If something went wrong, discard the useless Event
         ass_free_event(track, eid);
         track->n_events--;
@@ -1330,7 +1347,7 @@ void ass_process_chunk(ASS_Track *track, const char *data, int size,
 
         event->Start = timecode;
         event->Duration = duration;
-
+        update_prune_ts(track, event->Start + event->Duration);
         goto cleanup;
 //              dump_events(tid);
     } while (0);
@@ -1359,6 +1376,46 @@ void ass_flush_events(ASS_Track *track)
     track->parser_priv->read_order_elems = 0;
 }
 
+void ass_configure_prune(ASS_Track *track, long long delay)
+{
+    track->parser_priv->prune_delay = delay;
+}
+
+void ass_prune_events(ASS_Track *track, long long deadline)
+{
+    if (deadline < track->parser_priv->prune_next_ts)
+        return;
+
+    const bool check_readorder = track->parser_priv->check_readorder;
+    const int old_n_events = track->n_events;
+
+    int n_kept = 0;
+    ASS_Event *events = track->events;
+
+    track->parser_priv->prune_next_ts = LLONG_MAX;
+    for (int k = 0; k < old_n_events;) {
+        // discardable sequence
+        for (; k < old_n_events && events[k].Start + events[k].Duration < deadline; k++) {
+            if (check_readorder)
+                clear_read_order_bit(track, events[k].ReadOrder);
+            ass_free_event(track, k);
+        }
+
+        // to-be-kept sequence
+        int move_from = k;
+        for (long long ts; k < old_n_events && (ts = events[k].Start + events[k].Duration) >= deadline; k++)
+            update_prune_ts(track, ts);
+
+        // Relocate kept events
+        if (move_from < k) {
+            int cnt = k - move_from;
+            memmove(events + n_kept, events + move_from, cnt * sizeof(*track->events));
+            n_kept += cnt;
+        }
+    }
+    track->n_events = n_kept;
+}
+
 #ifdef CONFIG_ICONV
 /** \brief recode buffer to utf-8
  * constraint: codepage != 0
@@ -1725,6 +1782,8 @@ ASS_Track *ass_new_track(ASS_Library *library)
     if (!track->styles[def_sid].Name || !track->styles[def_sid].FontName)
         goto fail;
     track->parser_priv->check_readorder = 1;
+    track->parser_priv->prune_delay = -1;
+    track->parser_priv->prune_next_ts = LLONG_MAX;
     return track;
 
 fail:

libass/ass.h

@@ -24,7 +24,7 @@
 #include <stdarg.h>
 #include "ass_types.h"
 
-#define LIBASS_VERSION 0x01703000
+#define LIBASS_VERSION 0x01703010
 
 #ifdef __cplusplus
 extern "C" {
@@ -734,6 +734,24 @@ void ass_process_chunk(ASS_Track *track, const char *data, int size,
  */
 void ass_set_check_readorder(ASS_Track *track, int check_readorder);
 
+/**
+ * \brief Prune events that preceed deadline.
+ * \param track track
+ * \param deadline cut-off timestamp in milliseconds.
+*/
+void ass_prune_events(ASS_Track *track, long long deadline);
+
+/**
+ * \brief Configure automatic pruning of events.
+ * \param track track
+ * \param delay delay from "now" (ass_render_frame) in milliseconds.
+ * After every render, events whose undisplay timestamp predate
+ * "now - delay" will be deleted. A delay of 0 prunes aggressively.
+ * Negative delays disable automatic pruning.
+ * Disabled by default (no removal of events from memory).
+ */
+void ass_configure_prune(ASS_Track *track, long long delay);
+
 /**
  * \brief Flush buffered events.
  * \param track track

libass/ass_priv.h

@@ -65,6 +65,9 @@ struct parser_priv {
     uint32_t header_flags;
 
     uint32_t feature_flags;
+
+    long long prune_delay;
+    long long prune_next_ts;
 };
 
 #endif /* LIBASS_PRIV_H */

libass/ass_render.c

@@ -3428,6 +3428,9 @@ ASS_Image *ass_render_frame(ASS_Renderer *priv, ASS_Track *track,
     ass_frame_unref(priv->prev_images_root);
     priv->prev_images_root = NULL;
 
+    if (track->parser_priv->prune_delay >= 0)
+        ass_prune_events(track, now - track->parser_priv->prune_delay);
+
     return priv->images_root;
 }