BLI: add slice method to index mask and generic span

source/blender/blenlib/BLI_index_mask.hh

@@ -223,6 +223,7 @@ class IndexMask {
     return indices_.is_empty();
   }
 
+  IndexMask slice(IndexRange slice) const;
   IndexMask slice_and_offset(IndexRange slice, Vector<int64_t> &r_new_indices) const;
 };
 

source/blender/blenlib/intern/index_mask.cc

@@ -18,6 +18,11 @@
 
 namespace blender {
 
+IndexMask IndexMask::slice(IndexRange slice) const
+{
+  return IndexMask(indices_.slice(slice));
+}
+
 /**
  * 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.

source/blender/functions/FN_generic_span.hh

@@ -93,6 +93,11 @@ class GSpan {
     const int64_t new_size = std::max<int64_t>(0, std::min(size, size_ - start));
     return GSpan(*type_, POINTER_OFFSET(data_, type_->size() * start), new_size);
   }
+
+  GSpan slice(const IndexRange range) const
+  {
+    return this->slice(range.start(), range.size());
+  }
 };
 
 /**
@@ -169,6 +174,11 @@ class GMutableSpan {
     const int64_t new_size = std::max<int64_t>(0, std::min(size, size_ - start));
     return GMutableSpan(*type_, POINTER_OFFSET(data_, type_->size() * start), new_size);
   }
+
+  GMutableSpan slice(IndexRange range) const
+  {
+    return this->slice(range.start(), range.size());
+  }
 };
 
 }  // namespace blender::fn