1 files changed, 85 insertions, 0 deletions
diff --git a/source/blender/blenlib/BLI_virtual_list_list_ref.h b/source/blender/blenlib/BLI_virtual_list_list_ref.h
new file mode 100644
index 00000000000..ebcda7eb438
--- /dev/null
+++ b/source/blender/blenlib/BLI_virtual_list_list_ref.h
@@ -0,0 +1,85 @@
+#ifndef __BLI_VIRTUAL_ARRAY_LIST_REF_H__
+#define __BLI_VIRTUAL_ARRAY_LIST_REF_H__
+
+#include "BLI_virtual_list_ref.h"
+
+namespace BLI {
+
+template<typename T> class VirtualListListRef {
+ private:
+  enum Category {
+    SingleArray,
+    ListOfStartPointers,
+  };
+
+  uint m_virtual_size;
+  Category m_category;
+
+  union {
+    struct {
+      const T *start;
+      uint size;
+    } single_array;
+    struct {
+      const T *const *starts;
+      const uint *sizes;
+    } list_of_start_pointers;
+  } m_data;
+
+ public:
+  VirtualListListRef()
+  {
+    m_virtual_size = 0;
+    m_category = ListOfStartPointers;
+    m_data.list_of_start_pointers.starts = nullptr;
+    m_data.list_of_start_pointers.sizes = nullptr;
+  }
+
+  static VirtualListListRef FromSingleArray(ArrayRef<T> array, uint virtual_list_size)
+  {
+    VirtualListListRef list;
+    list.m_virtual_size = virtual_list_size;
+    list.m_category = Category::SingleArray;
+    list.m_data.single_array.start = array.begin();
+    list.m_data.single_array.size = array.size();
+    return list;
+  }
+
+  static VirtualListListRef FromListOfStartPointers(ArrayRef<const T *> starts,
+                                                    ArrayRef<uint> sizes)
+  {
+    assert_same_size(starts, sizes);
+    VirtualListListRef list;
+    list.m_virtual_size = starts.size();
+    list.m_category = Category::ListOfStartPointers;
+    list.m_data.list_of_start_pointers.starts = starts.begin();
+    list.m_data.list_of_start_pointers.sizes = sizes.begin();
+    return list;
+  }
+
+  uint size() const
+  {
+    return m_virtual_size;
+  }
+
+  VirtualListRef<T> operator[](uint index) const
+  {
+    BLI_assert(index < m_virtual_size);
+
+    switch (m_category) {
+      case Category::SingleArray:
+        return VirtualListRef<T>::FromFullArray(
+            ArrayRef<T>(m_data.single_array.start, m_data.single_array.size));
+      case Category::ListOfStartPointers:
+        return VirtualListRef<T>::FromFullArray(m_data.list_of_start_pointers.starts[index],
+                                                m_data.list_of_start_pointers.sizes[index]);
+    }
+
+    BLI_assert(false);
+    return {};
+  }
+};
+
+}  // namespace BLI
+
+#endif /* __BLI_VIRTUAL_ARRAY_LIST_REF_H__ */