From 6853d787dbe4dc203252bb55ee2be9f927d8ac4e Mon Sep 17 00:00:00 2001
From: Dalai Felinto <dalai@blender.org>
Date: Fri, 13 Oct 2023 10:08:51 +0200
Subject: [PATCH] Geometry Nodes: Util function to propagate attributes

This propagates from layer to instances, which is required by some
of the Grease Pencil nodes.

Part of #113602.
Ref !113634.
---
 source/blender/blenkernel/BKE_geometry_set.hh |  5 ++++
 .../blender/blenkernel/intern/geometry_set.cc | 27 +++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/source/blender/blenkernel/BKE_geometry_set.hh b/source/blender/blenkernel/BKE_geometry_set.hh
index a6f0d03b1b4..5022728e834 100644
--- a/source/blender/blenkernel/BKE_geometry_set.hh
+++ b/source/blender/blenkernel/BKE_geometry_set.hh
@@ -229,6 +229,11 @@ struct GeometrySet {
                          bool include_instances,
                          AttributeForeachCallback callback) const;
 
+  static void propagate_attributes_from_layer_to_instances(
+      const AttributeAccessor src_attributes,
+      MutableAttributeAccessor dst_attributes,
+      const AnonymousAttributePropagationInfo &propagation_info);
+
   void gather_attributes_for_propagation(Span<GeometryComponent::Type> component_types,
                                          GeometryComponent::Type dst_component_type,
                                          bool include_instances,
diff --git a/source/blender/blenkernel/intern/geometry_set.cc b/source/blender/blenkernel/intern/geometry_set.cc
index 66fef5bf69e..915df3f1078 100644
--- a/source/blender/blenkernel/intern/geometry_set.cc
+++ b/source/blender/blenkernel/intern/geometry_set.cc
@@ -605,6 +605,33 @@ void GeometrySet::attribute_foreach(const Span<GeometryComponent::Type> componen
   }
 }
 
+void GeometrySet::propagate_attributes_from_layer_to_instances(
+    const AttributeAccessor src_attributes,
+    MutableAttributeAccessor dst_attributes,
+    const AnonymousAttributePropagationInfo &propagation_info)
+{
+  src_attributes.for_all([&](const AttributeIDRef &id, const AttributeMetaData meta_data) {
+    if (id.is_anonymous() && !propagation_info.propagate(id.anonymous_id())) {
+      return true;
+    }
+    const GAttributeReader src = src_attributes.lookup(id, ATTR_DOMAIN_LAYER);
+    if (src.sharing_info && src.varray.is_span()) {
+      const AttributeInitShared init(src.varray.get_internal_span().data(), *src.sharing_info);
+      if (dst_attributes.add(id, ATTR_DOMAIN_INSTANCE, meta_data.data_type, init)) {
+        return true;
+      }
+    }
+    GSpanAttributeWriter dst = dst_attributes.lookup_or_add_for_write_only_span(
+        id, ATTR_DOMAIN_INSTANCE, meta_data.data_type);
+    if (!dst) {
+      return true;
+    }
+    array_utils::copy(src.varray, dst.span);
+    dst.finish();
+    return true;
+  });
+}
+
 void GeometrySet::gather_attributes_for_propagation(
     const Span<GeometryComponent::Type> component_types,
     const GeometryComponent::Type dst_component_type,