Fix T70612: Sequencer Crash on enabling Prefetch

Disable (skip) preftching scene strips if they target 3D scene.
Try to continue prefetching complete frame if disk cache images are found.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D7514

3 files changed, 75 insertions, 3 deletions

diff --git a/source/blender/blenkernel/BKE_sequencer.h b/source/blender/blenkernel/BKE_sequencer.h
index 5f0c10c9a5f..42032348370 100644
--- a/source/blender/blenkernel/BKE_sequencer.h
+++ b/source/blender/blenkernel/BKE_sequencer.h
@@ -277,6 +277,10 @@ void BKE_sequence_reload_new_file(struct Main *bmain,
                                   struct Sequence *seq,
                                   const bool lock_range);
 int BKE_sequencer_evaluate_frame(struct Scene *scene, int cfra);
+int BKE_sequencer_get_shown_sequences(struct ListBase *seqbasep,
+                                      int cfra,
+                                      int chanshown,
+                                      struct Sequence **seq_arr_out);
 
 struct StripElem *BKE_sequencer_give_stripelem(struct Sequence *seq, int cfra);
 
diff --git a/source/blender/blenkernel/intern/seqprefetch.c b/source/blender/blenkernel/intern/seqprefetch.c
index dabfd26f5b0..5eff6aaac90 100644
--- a/source/blender/blenkernel/intern/seqprefetch.c
+++ b/source/blender/blenkernel/intern/seqprefetch.c
@@ -334,6 +334,66 @@ void BKE_sequencer_prefetch_free(Scene *scene)
   scene->ed->prefetch_job = NULL;
 }
 
+static bool seq_prefetch_do_skip_frame(Scene *scene)
+{
+  Editing *ed = scene->ed;
+  PrefetchJob *pfjob = seq_prefetch_job_get(scene);
+  float cfra = pfjob->cfra + pfjob->num_frames_prefetched;
+  Sequence *seq_arr[MAXSEQ + 1];
+  int count = BKE_sequencer_get_shown_sequences(ed->seqbasep, cfra, 0, seq_arr);
+  SeqRenderData *ctx = &pfjob->context_cpy;
+  ImBuf *ibuf = NULL;
+
+  /* Disable prefetching 3D scene strips, but check for disk cache. */
+  for (int i = 0; i < count; i++) {
+    if (seq_arr[i]->type == SEQ_TYPE_SCENE && (seq_arr[i]->flag & SEQ_SCENE_STRIPS) == 0) {
+      int cached_types = 0;
+
+      ibuf = BKE_sequencer_cache_get(ctx, seq_arr[i], cfra, SEQ_CACHE_STORE_FINAL_OUT, false);
+      if (ibuf != NULL) {
+        cached_types |= SEQ_CACHE_STORE_FINAL_OUT;
+        IMB_freeImBuf(ibuf);
+        ibuf = NULL;
+      }
+
+      ibuf = BKE_sequencer_cache_get(ctx, seq_arr[i], cfra, SEQ_CACHE_STORE_FINAL_OUT, false);
+      if (ibuf != NULL) {
+        cached_types |= SEQ_CACHE_STORE_COMPOSITE;
+        IMB_freeImBuf(ibuf);
+        ibuf = NULL;
+      }
+
+      ibuf = BKE_sequencer_cache_get(ctx, seq_arr[i], cfra, SEQ_CACHE_STORE_PREPROCESSED, false);
+      if (ibuf != NULL) {
+        cached_types |= SEQ_CACHE_STORE_PREPROCESSED;
+        IMB_freeImBuf(ibuf);
+        ibuf = NULL;
+      }
+
+      ibuf = BKE_sequencer_cache_get(ctx, seq_arr[i], cfra, SEQ_CACHE_STORE_RAW, false);
+      if (ibuf != NULL) {
+        cached_types |= SEQ_CACHE_STORE_RAW;
+        IMB_freeImBuf(ibuf);
+        ibuf = NULL;
+      }
+
+      if ((cached_types & (SEQ_CACHE_STORE_RAW | SEQ_CACHE_STORE_PREPROCESSED)) != 0) {
+        continue;
+      }
+
+      /* It is only safe to use these cache types if strip is last in stack. */
+      if (i == count - 1 &&
+          (cached_types & (SEQ_CACHE_STORE_PREPROCESSED | SEQ_CACHE_STORE_RAW)) != 0) {
+        continue;
+      }
+
+      return true;
+    }
+  }
+
+  return false;
+}
+
 static void *seq_prefetch_frames(void *job)
 {
   PrefetchJob *pfjob = (PrefetchJob *)job;
@@ -358,6 +418,11 @@ static void *seq_prefetch_frames(void *job)
      */
     pfjob->scene_eval->ed->prefetch_job = pfjob;
 
+    if (seq_prefetch_do_skip_frame(pfjob->scene)) {
+      pfjob->num_frames_prefetched++;
+      continue;
+    }
+
     ImBuf *ibuf = BKE_sequencer_give_ibuf(
         &pfjob->context_cpy, pfjob->cfra + pfjob->num_frames_prefetched, 0);
     BKE_sequencer_cache_free_temp_cache(
diff --git a/source/blender/blenkernel/intern/sequencer.c b/source/blender/blenkernel/intern/sequencer.c
index 6791424694a..53357546669 100644
--- a/source/blender/blenkernel/intern/sequencer.c
+++ b/source/blender/blenkernel/intern/sequencer.c
@@ -1538,7 +1538,10 @@ static bool video_seq_is_rendered(Sequence *seq)
   return (seq && !(seq->flag & SEQ_MUTE) && seq->type != SEQ_TYPE_SOUND_RAM);
 }
 
-static int get_shown_sequences(ListBase *seqbasep, int cfra, int chanshown, Sequence **seq_arr_out)
+int BKE_sequencer_get_shown_sequences(ListBase *seqbasep,
+                                      int cfra,
+                                      int chanshown,
+                                      Sequence **seq_arr_out)
 {
   Sequence *seq_arr[MAXSEQ + 1];
   int b = chanshown;
@@ -3973,7 +3976,7 @@ static ImBuf *seq_render_strip_stack(const SeqRenderData *context,
   ImBuf *out = NULL;
   clock_t begin;
 
-  count = get_shown_sequences(seqbasep, cfra, chanshown, (Sequence **)&seq_arr);
+  count = BKE_sequencer_get_shown_sequences(seqbasep, cfra, chanshown, (Sequence **)&seq_arr);
 
   if (count == 0) {
     return NULL;
@@ -4081,7 +4084,7 @@ ImBuf *BKE_sequencer_give_ibuf(const SeqRenderData *context, float cfra, int cha
   Sequence *seq_arr[MAXSEQ + 1];
   int count;
 
-  count = get_shown_sequences(seqbasep, cfra, chanshown, seq_arr);
+  count = BKE_sequencer_get_shown_sequences(seqbasep, cfra, chanshown, seq_arr);
 
   if (count) {
     out = BKE_sequencer_cache_get(