From 8fe9c40a07bb53dcfe435ce6b24bdc69bf56cae0 Mon Sep 17 00:00:00 2001
From: Hans Goudey <h.goudey@me.com>
Date: Thu, 20 Apr 2023 13:11:04 -0400
Subject: [PATCH] Fix #107185: Set position node skips setting rest positions

Now attributes can use the same arrays, checking their data pointers
isn't enough to tell them apart. After e45ed69349af24ba6786, the rest
position attribute is created sharing the same array as positions,
which meant the optimization to skip reading the position input to
the set position node failed. Fix that by checking if the field is the
position attribute instead.
---
 .../geometry/nodes/node_geo_set_position.cc   | 24 +++++++++++--------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/source/blender/nodes/geometry/nodes/node_geo_set_position.cc b/source/blender/nodes/geometry/nodes/node_geo_set_position.cc
index 428bf42ae40..0dd546272e5 100644
--- a/source/blender/nodes/geometry/nodes/node_geo_set_position.cc
+++ b/source/blender/nodes/geometry/nodes/node_geo_set_position.cc
@@ -26,18 +26,10 @@ static void node_declare(NodeDeclarationBuilder &b)
 static void set_computed_position_and_offset(GeometryComponent &component,
                                              const VArray<float3> &in_positions,
                                              const VArray<float3> &in_offsets,
+                                             const bool positions_are_original,
                                              const IndexMask selection)
 {
   MutableAttributeAccessor attributes = *component.attributes_for_write();
-
-  /* Optimize the case when `in_positions` references the original positions array. */
-  const bke::AttributeReader positions_read_only = attributes.lookup<float3>("position");
-  bool positions_are_original = false;
-  if (positions_read_only.varray.is_span() && in_positions.is_span()) {
-    positions_are_original = positions_read_only.varray.get_internal_span().data() ==
-                             in_positions.get_internal_span().data();
-  }
-
   if (positions_are_original) {
     if (const std::optional<float3> offset = in_offsets.get_if_single()) {
       if (math::is_zero(*offset)) {
@@ -116,6 +108,15 @@ static void set_computed_position_and_offset(GeometryComponent &component,
   }
 }
 
+static bool field_is_positions(const Field<float3> &field)
+{
+  const auto *attribute_field = dynamic_cast<const bke::AttributeFieldInput *>(&field.node());
+  if (!attribute_field) {
+    return false;
+  }
+  return attribute_field->attribute_name() == "position";
+}
+
 static void set_position_in_component(GeometrySet &geometry,
                                       GeometryComponentType component_type,
                                       const Field<bool> &selection_field,
@@ -143,10 +144,13 @@ static void set_position_in_component(GeometrySet &geometry,
     return;
   }
 
+  const bool positions_are_original = field_is_positions(position_field);
+
   GeometryComponent &mutable_component = geometry.get_component_for_write(component_type);
   const VArray<float3> positions_input = evaluator.get_evaluated<float3>(0);
   const VArray<float3> offsets_input = evaluator.get_evaluated<float3>(1);
-  set_computed_position_and_offset(mutable_component, positions_input, offsets_input, selection);
+  set_computed_position_and_offset(
+      mutable_component, positions_input, offsets_input, positions_are_original, selection);
 }
 
 static void node_geo_exec(GeoNodeExecParams params)
-- 
2.30.2