Geometry: Avoid unnecessary initialization when resizing data arrays

When resizing mesh and curves attribute storage, avoid initializing the
new memory for basic types. Also, avoid skipping "no free" layers; all
layers should be reallocated to the new size since they may be accessed.

The semantics introduced in 25237d2625078c6d1 are essential for this
change, because otherwise we don't have a way to construct non-trivial
types in the new memory.

In a basic test of the extrude node, I observed a performance
improvement of about 30%, from 55ms to 42ms.

Differential Revision: https://developer.blender.org/D15818

1 files changed, 15 insertions, 1 deletions

diff --git a/source/blender/blenkernel/intern/attribute_access.cc b/source/blender/blenkernel/intern/attribute_access.cc
index 69f3e5bb389..27c54a3d4a7 100644
--- a/source/blender/blenkernel/intern/attribute_access.cc
+++ b/source/blender/blenkernel/intern/attribute_access.cc
@@ -726,8 +726,22 @@ bool CustomDataAttributes::remove(const AttributeIDRef &attribute_id)
 
 void CustomDataAttributes::reallocate(const int size)
 {
+  const int old_size = size_;
   size_ = size;
-  CustomData_realloc(&data, size);
+  CustomData_realloc(&data, old_size, size_);
+  if (size_ > old_size) {
+    /* Fill default new values. */
+    const int new_elements_num = size_ - old_size;
+    this->foreach_attribute(
+        [&](const bke::AttributeIDRef &id, const bke::AttributeMetaData /*meta_data*/) {
+          GMutableSpan new_data = this->get_for_write(id)->take_back(new_elements_num);
+          const CPPType &type = new_data.type();
+          type.fill_assign_n(type.default_value(), new_data.data(), new_data.size());
+          return true;
+        },
+        /* Dummy. */
+        ATTR_DOMAIN_POINT);
+  }
 }
 
 void CustomDataAttributes::clear()