VSE: Make cache eviction a bit smarter when wrapping.

Also fix some minor cache and prefetch bugs that became more noticeable
with these changes.

Pull Request: https://projects.blender.org/blender/blender/pulls/139635

source/blender/sequencer/intern/cache/final_image_cache.cc

@@ -200,17 +200,20 @@ bool final_image_cache_evict(Scene *scene)
     /* Only activate the prefetch guards if the cache is active. */
     seq_prefetch_get_time_range(scene, &cur_prefetch_start, &cur_prefetch_end);
   }
-  bool prefetch_loops_around = cur_prefetch_start > cur_prefetch_end;
+  const bool prefetch_loops_around = cur_prefetch_start > cur_prefetch_end;
+
+  const int timeline_start = PSFRA;
+  const int timeline_end = PEFRA;
+  /* If we wrap around, treat the timeline start as the playback head position.
+   * This is to try to mitigate un-needed cache evictions. */
+  const int cur_frame = prefetch_loops_around ? timeline_start : scene->r.cfra;
 
-  const int cur_frame = scene->r.cfra;
   std::pair<int, int> best_key = {};
   ImBuf *best_item = nullptr;
   int best_score = 0;
   for (const auto &item : cache->map_.items()) {
     const int item_frame = item.key.first;
     if (prefetch_loops_around) {
-      int timeline_start = PSFRA;
-      int timeline_end = PEFRA;
       if (item_frame >= timeline_start && item_frame <= cur_prefetch_end) {
         continue; /* Within active prefetch range, do not try to remove it. */
       }

source/blender/sequencer/intern/cache/source_image_cache.cc

@@ -268,9 +268,14 @@ bool source_image_cache_evict(Scene *scene)
     /* Only activate the prefetch guards if the cache is active. */
     seq_prefetch_get_time_range(scene, &cur_prefetch_start, &cur_prefetch_end);
   }
-  bool prefetch_loops_around = cur_prefetch_start > cur_prefetch_end;
+  const bool prefetch_loops_around = cur_prefetch_start > cur_prefetch_end;
+
+  const int timeline_start = PSFRA;
+  const int timeline_end = PEFRA;
+  /* If we wrap around, treat the timeline start as the playback head position.
+   * This is to try to mitigate un-needed cache evictions. */
+  const int cur_frame = prefetch_loops_around ? timeline_start : scene->r.cfra;
 
-  const int cur_frame = scene->r.cfra;
   SourceImageCache::StripEntry *best_strip = nullptr;
   std::pair<int, int> best_key = {};
   int best_score = 0;
@@ -278,8 +283,6 @@ bool source_image_cache_evict(Scene *scene)
     for (const auto &entry : strip.value.frames.items()) {
       const int item_frame = int(strip.key->start + entry.value.strip_frame);
       if (prefetch_loops_around) {
-        int timeline_start = PSFRA;
-        int timeline_end = PEFRA;
         if (item_frame >= timeline_start && item_frame <= cur_prefetch_end) {
           continue; /* Within active prefetch range, do not try to remove it. */
         }

source/blender/sequencer/intern/prefetch.cc

@@ -76,7 +76,7 @@ struct PrefetchJob {
   int timeline_end = 0;
   int timeline_length = 0;
   int num_frames_prefetched = 0;
-  int cache_flags = 0;
+  int cache_flags = 0; /* Only used to detect cache flag changes. */
 
   /* Control: */
   /* Set by prefetch. */
@@ -544,6 +544,7 @@ static void *seq_prefetch_frames(void *job)
     }
 
     ImBuf *ibuf = render_give_ibuf(&pfjob->context_cpy, seq_prefetch_cfra(pfjob), 0);
+    pfjob->num_frames_prefetched++;
     IMB_freeImBuf(ibuf);
 
     /* Suspend thread if there is nothing to be prefetched. */
@@ -556,7 +557,6 @@ static void *seq_prefetch_frames(void *job)
     }
 
     seq_prefetch_update_area(pfjob);
-    pfjob->num_frames_prefetched++;
   }
 
   pfjob->running = false;

source/blender/sequencer/intern/render.cc

@@ -2004,10 +2004,12 @@ ImBuf *render_give_ibuf(const RenderData *context, float timeline_frame, int cha
 
   if (!strips.is_empty() && !out) {
     std::scoped_lock lock(seq_render_mutex);
-    out = seq_render_strip_stack(context, &state, channels, seqbasep, timeline_frame, chanshown);
-
+    /* Try to make space before we add any new frames to the cache if it is full.
+     * If we do this after we have added the new cache, we risk removing what we just added.*/
     evict_caches_if_full(orig_scene);
 
+    out = seq_render_strip_stack(context, &state, channels, seqbasep, timeline_frame, chanshown);
+
     if (out && (orig_scene->ed->cache_flag & SEQ_CACHE_STORE_FINAL_OUT) && !context->skip_cache &&
         !context->is_proxy_render)
     {

source/blender/sequencer/intern/strip_relations.cc

@@ -94,11 +94,12 @@ bool evict_caches_if_full(Scene *scene)
   bool evicted_source = false;
   if (count_source != 0) {
     evicted_source = source_image_cache_evict(scene);
+    /* Only try to enforce the final frame and raw cache ratio when the final cache is active. */
     if (evicted_source && scene->ed->cache_flag & SEQ_CACHE_STORE_FINAL_OUT) {
-      /* Only try to enforce the final frame and raw cache ratio when the final cache is active. */
-      const size_t source_per_final = divide_ceil_ul(count_source - 1,
+      const size_t source_per_final = divide_ceil_ul(count_source,
                                                      std::max<size_t>(count_final, 1));
-      for (size_t i = 0; i < source_per_final; i++) {
+      /* Start at "1" to make sure we only try to evict more frames if the ratio is above 1:1. */
+      for (size_t i = 1; i < source_per_final; i++) {
         if (!source_image_cache_evict(scene)) {
           /* Can't evict any more frames, stop. */
           break;