1 files changed, 82 insertions, 10 deletions

diff --git a/intern/cycles/render/alembic.h b/intern/cycles/render/alembic.h
index 6552336e6ab..0fc02f1da23 100644
--- a/intern/cycles/render/alembic.h
+++ b/intern/cycles/render/alembic.h
@@ -50,6 +50,78 @@ template<typename> struct is_array : public std::false_type {
 template<typename T> struct is_array<array<T>> : public std::true_type {
 };
 
+/* Holds the data for a cache lookup at a given time, as well as informations to
+ * help disambiguate successes or failures to get data from the cache. */
+template<typename T> class CacheLookupResult {
+  enum class State {
+    NEW_DATA,
+    ALREADY_LOADED,
+    NO_DATA_FOR_TIME,
+  };
+
+  T *data;
+  State state;
+
+ protected:
+  /* Prevent default construction outside of the class: for a valid result, we
+   * should use the static functions below. */
+  CacheLookupResult() = default;
+
+ public:
+  static CacheLookupResult new_data(T *data_)
+  {
+    CacheLookupResult result;
+    result.data = data_;
+    result.state = State::NEW_DATA;
+    return result;
+  }
+
+  static CacheLookupResult no_data_found_for_time()
+  {
+    CacheLookupResult result;
+    result.data = nullptr;
+    result.state = State::NO_DATA_FOR_TIME;
+    return result;
+  }
+
+  static CacheLookupResult already_loaded()
+  {
+    CacheLookupResult result;
+    result.data = nullptr;
+    result.state = State::ALREADY_LOADED;
+    return result;
+  }
+
+  /* This should only be call if new data is available. */
+  const T &get_data() const
+  {
+    assert(state == State::NEW_DATA);
+    assert(data != nullptr);
+    return *data;
+  }
+
+  T *get_data_or_null() const
+  {
+    // data_ should already be null if there is no new data so no need to check
+    return data;
+  }
+
+  bool has_new_data() const
+  {
+    return state == State::NEW_DATA;
+  }
+
+  bool has_already_loaded() const
+  {
+    return state == State::ALREADY_LOADED;
+  }
+
+  bool has_no_data_for_time() const
+  {
+    return state == State::NO_DATA_FOR_TIME;
+  }
+};
+
 /* Store the data set for an animation at every time points, or at the beginning of the animation
  * for constant data.
  *
@@ -79,10 +151,10 @@ template<typename T> class DataStore {
 
   /* Get the data for the specified time.
    * Return nullptr if there is no data or if the data for this time was already loaded. */
-  T *data_for_time(double time)
+  CacheLookupResult<T> data_for_time(double time)
   {
     if (size() == 0) {
-      return nullptr;
+      return CacheLookupResult<T>::no_data_found_for_time();
     }
 
     std::pair<size_t, Alembic::Abc::chrono_t> index_pair;
@@ -90,26 +162,26 @@ template<typename T> class DataStore {
     DataTimePair &data_pair = data[index_pair.first];
 
     if (last_loaded_time == data_pair.time) {
-      return nullptr;
+      return CacheLookupResult<T>::already_loaded();
     }
 
     last_loaded_time = data_pair.time;
 
-    return &data_pair.data;
+    return CacheLookupResult<T>::new_data(&data_pair.data);
   }
 
   /* get the data for the specified time, but do not check if the data was already loaded for this
    * time return nullptr if there is no data */
-  T *data_for_time_no_check(double time)
+  CacheLookupResult<T> data_for_time_no_check(double time)
   {
     if (size() == 0) {
-      return nullptr;
+      return CacheLookupResult<T>::no_data_found_for_time();
     }
 
     std::pair<size_t, Alembic::Abc::chrono_t> index_pair;
     index_pair = time_sampling.getNearIndex(time, data.size());
     DataTimePair &data_pair = data[index_pair.first];
-    return &data_pair.data;
+    return CacheLookupResult<T>::new_data(&data_pair.data);
   }
 
   void add_data(T &data_, double time)
@@ -149,15 +221,15 @@ template<typename T> class DataStore {
    * data for this time or it was already loaded, do nothing. */
   void copy_to_socket(double time, Node *node, const SocketType *socket)
   {
-    T *data_ = data_for_time(time);
+    CacheLookupResult<T> result = data_for_time(time);
 
-    if (data_ == nullptr) {
+    if (!result.has_new_data()) {
       return;
     }
 
     /* TODO(kevindietrich): arrays are emptied when passed to the sockets, so for now we copy the
      * arrays to avoid reloading the data */
-    T value = *data_;
+    T value = result.get_data();
     node->set(*socket, value);
   }
 };