1 files changed, 21 insertions, 2 deletions
diff --git a/source/blender/blenlib/BLI_index_mask.hh b/source/blender/blenlib/BLI_index_mask.hh
index ad030e127fe..2dca3689cb1 100644
--- a/source/blender/blenlib/BLI_index_mask.hh
+++ b/source/blender/blenlib/BLI_index_mask.hh
@@ -45,11 +45,11 @@ namespace blender {
 
 class IndexMask {
  private:
-  /* The underlying reference to sorted integers. */
+  /** The underlying reference to sorted integers. */
   Span<int64_t> indices_;
 
  public:
-  /* Creates an IndexMask that contains no indices. */
+  /** Creates an IndexMask that contains no indices. */
   IndexMask() = default;
 
   /**
@@ -223,6 +223,25 @@ class IndexMask {
     return indices_.is_empty();
   }
 
+  IndexMask slice(IndexRange slice) const;
+  /**
+   * Create a sub-mask that is also shifted to the beginning.
+   * The shifting to the beginning allows code to work with smaller indices,
+   * which is more memory efficient.
+   *
+   * \return New index mask with the size of #slice. It is either empty or starts with 0.
+   * It might reference indices that have been appended to #r_new_indices.
+   *
+   * Example:
+   * \code{.unparsed}
+   * this:   [2, 3, 5, 7, 8, 9, 10]
+   * slice:      ^--------^
+   * output: [0, 2, 4, 5]
+   * \endcode
+   *
+   * All the indices in the sub-mask are shifted by 3 towards zero,
+   * so that the first index in the output is zero.
+   */
   IndexMask slice_and_offset(IndexRange slice, Vector<int64_t> &r_new_indices) const;
 };