Outliner: Refactor outliner tree-hash interfaces with C++

- Turn storage into an object with "automatic" memory management (RAII)
  so freeing is implicit and reliable.
- Turn functions into member functions, to have the data and its
  functions close together with controlled access that increases
  encapsulation and hiding implementation details.
- Use references to indicate null is not an expected value.
- Related minor cleanup (comments, use const etc.)

Couldn't spot any changes in performance.

4 files changed, 23 insertions, 33 deletions

diff --git a/source/blender/editors/space_outliner/outliner_intern.hh b/source/blender/editors/space_outliner/outliner_intern.hh
index 5362782dd84..80254a5cb88 100644
--- a/source/blender/editors/space_outliner/outliner_intern.hh
+++ b/source/blender/editors/space_outliner/outliner_intern.hh
@@ -42,21 +42,25 @@ class AbstractTreeDisplay;
 class AbstractTreeElement;
 }  // namespace blender::ed::outliner
 
+namespace blender::bke::outliner::treehash {
+class TreeHash;
+}
+
 namespace outliner = blender::ed::outliner;
+namespace treehash = blender::bke::outliner::treehash;
 
 struct SpaceOutliner_Runtime {
   /** Object to create and manage the tree for a specific display type (View Layers, Scenes,
    * Blender File, etc.). */
   std::unique_ptr<outliner::AbstractTreeDisplay> tree_display;
 
-  /** Pointers to tree-store elements, grouped by `(id, type, nr)`
-   *  in hash-table for faster searching. */
-  struct GHash *treehash;
+  /* Hash table for tree-store elements, using `(id, type, index)` as key. */
+  std::unique_ptr<treehash::TreeHash> tree_hash;
 
   SpaceOutliner_Runtime() = default;
   /** Used for copying runtime data to a duplicated space. */
   SpaceOutliner_Runtime(const SpaceOutliner_Runtime &);
-  ~SpaceOutliner_Runtime();
+  ~SpaceOutliner_Runtime() = default;
 };
 
 typedef enum TreeElementInsertType {
diff --git a/source/blender/editors/space_outliner/outliner_tree.cc b/source/blender/editors/space_outliner/outliner_tree.cc
index b3b2bb59e20..05df3f9cb8f 100644
--- a/source/blender/editors/space_outliner/outliner_tree.cc
+++ b/source/blender/editors/space_outliner/outliner_tree.cc
@@ -111,10 +111,7 @@ static void outliner_storage_cleanup(SpaceOutliner *space_outliner)
         if (BLI_mempool_len(ts) == unused) {
           BLI_mempool_destroy(ts);
           space_outliner->treestore = nullptr;
-          if (space_outliner->runtime->treehash) {
-            BKE_outliner_treehash_free(space_outliner->runtime->treehash);
-            space_outliner->runtime->treehash = nullptr;
-          }
+          space_outliner->runtime->tree_hash = nullptr;
         }
         else {
           TreeStoreElem *tsenew;
@@ -129,16 +126,15 @@ static void outliner_storage_cleanup(SpaceOutliner *space_outliner)
           }
           BLI_mempool_destroy(ts);
           space_outliner->treestore = new_ts;
-          if (space_outliner->runtime->treehash) {
+          if (space_outliner->runtime->tree_hash) {
             /* update hash table to fix broken pointers */
-            BKE_outliner_treehash_rebuild_from_treestore(space_outliner->runtime->treehash,
-                                                         space_outliner->treestore);
+            space_outliner->runtime->tree_hash->rebuild_from_treestore(*space_outliner->treestore);
           }
         }
       }
     }
-    else if (space_outliner->runtime->treehash) {
-      BKE_outliner_treehash_clear_used(space_outliner->runtime->treehash);
+    else if (space_outliner->runtime->tree_hash) {
+      space_outliner->runtime->tree_hash->clear_used();
     }
   }
 }
@@ -151,15 +147,14 @@ static void check_persistent(
     space_outliner->treestore = BLI_mempool_create(
         sizeof(TreeStoreElem), 1, 512, BLI_MEMPOOL_ALLOW_ITER);
   }
-  if (space_outliner->runtime->treehash == nullptr) {
-    space_outliner->runtime->treehash = static_cast<GHash *>(
-        BKE_outliner_treehash_create_from_treestore(space_outliner->treestore));
+  if (space_outliner->runtime->tree_hash == nullptr) {
+    space_outliner->runtime->tree_hash = treehash::TreeHash::create_from_treestore(
+        *space_outliner->treestore);
   }
 
   /* find any unused tree element in treestore and mark it as used
    * (note that there may be multiple unused elements in case of linked objects) */
-  TreeStoreElem *tselem = BKE_outliner_treehash_lookup_unused(
-      space_outliner->runtime->treehash, type, nr, id);
+  TreeStoreElem *tselem = space_outliner->runtime->tree_hash->lookup_unused(type, nr, id);
   if (tselem) {
     te->store_elem = tselem;
     tselem->used = 1;
@@ -174,7 +169,7 @@ static void check_persistent(
   tselem->used = 0;
   tselem->flag = TSE_CLOSED;
   te->store_elem = tselem;
-  BKE_outliner_treehash_add_element(space_outliner->runtime->treehash, tselem);
+  space_outliner->runtime->tree_hash->add_element(*tselem);
 }
 
 /** \} */
@@ -1685,10 +1680,9 @@ void outliner_build_tree(Main *mainvar,
     space_outliner->search_flags &= ~SO_SEARCH_RECURSIVE;
   }
 
-  if (space_outliner->runtime->treehash && (space_outliner->storeflag & SO_TREESTORE_REBUILD) &&
+  if (space_outliner->runtime->tree_hash && (space_outliner->storeflag & SO_TREESTORE_REBUILD) &&
       space_outliner->treestore) {
-    BKE_outliner_treehash_rebuild_from_treestore(space_outliner->runtime->treehash,
-                                                 space_outliner->treestore);
+    space_outliner->runtime->tree_hash->rebuild_from_treestore(*space_outliner->treestore);
   }
   space_outliner->storeflag &= ~SO_TREESTORE_REBUILD;
 
diff --git a/source/blender/editors/space_outliner/outliner_utils.cc b/source/blender/editors/space_outliner/outliner_utils.cc
index 9c1425befdd..2ce017f4f64 100644
--- a/source/blender/editors/space_outliner/outliner_utils.cc
+++ b/source/blender/editors/space_outliner/outliner_utils.cc
@@ -184,8 +184,7 @@ TreeElement *outliner_find_tse(SpaceOutliner *space_outliner, const TreeStoreEle
   }
 
   /* Check if 'tse' is in tree-store. */
-  tselem = BKE_outliner_treehash_lookup_any(
-      space_outliner->runtime->treehash, tse->type, tse->nr, tse->id);
+  tselem = space_outliner->runtime->tree_hash->lookup_any(tse->type, tse->nr, tse->id);
   if (tselem) {
     return outliner_find_tree_element(&space_outliner->tree, tselem);
   }
diff --git a/source/blender/editors/space_outliner/space_outliner.cc b/source/blender/editors/space_outliner/space_outliner.cc
index 2435e804ed5..66ee0f4f3af 100644
--- a/source/blender/editors/space_outliner/space_outliner.cc
+++ b/source/blender/editors/space_outliner/space_outliner.cc
@@ -38,17 +38,10 @@
 #include "tree/tree_display.hh"
 
 SpaceOutliner_Runtime::SpaceOutliner_Runtime(const SpaceOutliner_Runtime & /*other*/)
-    : tree_display(nullptr), treehash(nullptr)
+    : tree_display(nullptr), tree_hash(nullptr)
 {
 }
 
-SpaceOutliner_Runtime::~SpaceOutliner_Runtime()
-{
-  if (treehash) {
-    BKE_outliner_treehash_free(treehash);
-  }
-}
-
 static void outliner_main_region_init(wmWindowManager *wm, ARegion *region)
 {
   ListBase *lb;
@@ -418,7 +411,7 @@ static void outliner_id_remap(ScrArea *area, SpaceLink *slink, const struct IDRe
 
   /* Note that the Outliner may not be the active editor of the area, and hence not initialized.
    * So runtime data might not have been created yet. */
-  if (space_outliner->runtime && space_outliner->runtime->treehash && changed) {
+  if (space_outliner->runtime && space_outliner->runtime->tree_hash && changed) {
     /* rebuild hash table, because it depends on ids too */
     /* postpone a full rebuild because this can be called many times on-free */
     space_outliner->storeflag |= SO_TREESTORE_REBUILD;