Fix: Geometry Nodes: crash when converting layers to instances

The crash/assert happened because the case when there are instances already was not handled.

Pull Request: https://projects.blender.org/blender/blender/pulls/127299

source/blender/blenkernel/BKE_geometry_set.hh

@@ -658,6 +658,8 @@ class InstancesComponent : public GeometryComponent {
 
   bool is_empty() const final;
 
+  Instances *release();
+
   bool owns_direct_data() const override;
   void ensure_owns_direct_data() override;
 

source/blender/blenkernel/intern/geometry_component_instances.cc

@@ -102,6 +102,14 @@ void InstancesComponent::replace(Instances *instances, GeometryOwnershipType own
   ownership_ = ownership;
 }
 
+Instances *InstancesComponent::release()
+{
+  BLI_assert(this->is_mutable());
+  Instances *instance = instances_;
+  instances_ = nullptr;
+  return instance;
+}
+
 void InstancesComponent::count_memory(MemoryCounter &memory) const
 {
   if (instances_) {

source/blender/nodes/geometry/nodes/node_geo_curve_to_mesh.cc

@@ -10,6 +10,7 @@
 
 #include "UI_resources.hh"
 
+#include "GEO_join_geometries.hh"
 #include "GEO_randomize.hh"
 
 #include "node_geometry_util.hh"
@@ -70,13 +71,7 @@ static void grease_pencil_to_mesh(GeometrySet &geometry_set,
     return;
   }
 
-  InstancesComponent &instances_component =
-      geometry_set.get_component_for_write<InstancesComponent>();
-  bke::Instances *instances = instances_component.get_for_write();
-  if (instances == nullptr) {
-    instances = new bke::Instances();
-    instances_component.replace(instances);
-  }
+  bke::Instances *instances = new bke::Instances();
   for (Mesh *mesh : mesh_by_layer) {
     if (!mesh) {
       /* Add an empty reference so the number of layers and instances match.
@@ -92,8 +87,14 @@ static void grease_pencil_to_mesh(GeometrySet &geometry_set,
   }
   GeometrySet::propagate_attributes_from_layer_to_instances(
       geometry_set.get_grease_pencil()->attributes(),
-      geometry_set.get_instances_for_write()->attributes_for_write(),
+      instances->attributes_for_write(),
       attribute_filter);
+  InstancesComponent &dst_component = geometry_set.get_component_for_write<InstancesComponent>();
+  GeometrySet new_instances = geometry::join_geometries(
+      {GeometrySet::from_instances(dst_component.release()),
+       GeometrySet::from_instances(instances)},
+      attribute_filter);
+  dst_component.replace(new_instances.get_component_for_write<InstancesComponent>().release());
   geometry_set.replace_grease_pencil(nullptr);
 }
 

source/blender/nodes/geometry/nodes/node_geo_curve_to_points.cc

@@ -13,6 +13,7 @@
 #include "BKE_instances.hh"
 #include "BKE_pointcloud.hh"
 
+#include "GEO_join_geometries.hh"
 #include "GEO_resample_curves.hh"
 
 #include "NOD_rna_define.hh"
@@ -272,13 +273,7 @@ static void grease_pencil_to_points(GeometrySet &geometry_set,
                                                                   rotation_anonymous_id);
       }
       if (!pointcloud_by_layer.is_empty()) {
-        InstancesComponent &instances_component =
-            geometry_set.get_component_for_write<InstancesComponent>();
-        bke::Instances *instances = instances_component.get_for_write();
-        if (instances == nullptr) {
-          instances = new bke::Instances();
-          instances_component.replace(instances);
-        }
+        bke::Instances *instances = new bke::Instances();
         for (PointCloud *pointcloud : pointcloud_by_layer) {
           if (!pointcloud) {
             /* Add an empty reference so the number of layers and instances match.
@@ -294,8 +289,15 @@ static void grease_pencil_to_points(GeometrySet &geometry_set,
         }
         GeometrySet::propagate_attributes_from_layer_to_instances(
             geometry.get_grease_pencil()->attributes(),
-            geometry.get_instances_for_write()->attributes_for_write(),
+            instances->attributes_for_write(),
             attribute_filter);
+        InstancesComponent &dst_component = geometry.get_component_for_write<InstancesComponent>();
+        GeometrySet new_instances = geometry::join_geometries(
+            {GeometrySet::from_instances(dst_component.release()),
+             GeometrySet::from_instances(instances)},
+            attribute_filter);
+        dst_component.replace(
+            new_instances.get_component_for_write<InstancesComponent>().release());
       }
     }
   });

source/blender/nodes/geometry/nodes/node_geo_instance_on_points.cc

@@ -12,6 +12,8 @@
 #include "BKE_grease_pencil.hh"
 #include "BKE_instances.hh"
 
+#include "GEO_join_geometries.hh"
+
 #include "node_geometry_util.hh"
 
 namespace blender::nodes::node_geo_instance_on_points_cc {
@@ -225,6 +227,7 @@ static void node_geo_exec(GeoNodeExecParams params)
     if (geometry_set.has_grease_pencil()) {
       using namespace bke::greasepencil;
       const GreasePencil &grease_pencil = *geometry_set.get_grease_pencil();
+      bke::Instances *instances = new bke::Instances();
       for (const int layer_index : grease_pencil.layers().index_range()) {
         const Drawing *drawing = grease_pencil.get_eval_drawing(grease_pencil.layer(layer_index));
         if (drawing == nullptr) {
@@ -235,30 +238,35 @@ static void node_geo_exec(GeoNodeExecParams params)
           /* Add an empty reference so the number of layers and instances match.
            * This makes it easy to reconstruct the layers afterwards and keep their attributes.
            * Although in this particular case we don't propagate the attributes. */
-          const int handle = dst_instances->add_reference(bke::InstanceReference());
-          dst_instances->add_instance(handle, float4x4::identity());
+          const int handle = instances->add_reference(bke::InstanceReference());
+          instances->add_instance(handle, float4x4::identity());
           continue;
         }
         /* TODO: Attributes are not propagating from the curves or the points. */
-        bke::Instances *instances = new bke::Instances();
+        bke::Instances *layer_instances = new bke::Instances();
         const bke::GreasePencilLayerFieldContext field_context(
             grease_pencil, AttrDomain::Point, layer_index);
-        add_instances_from_component(*instances,
+        add_instances_from_component(*layer_instances,
                                      src_curves.attributes(),
                                      instance,
                                      field_context,
                                      params,
                                      attributes_to_propagate);
-        GeometrySet temp_set = GeometrySet::from_instances(instances);
-        const int handle = dst_instances->add_reference(bke::InstanceReference{temp_set});
-        dst_instances->add_instance(handle, float4x4::identity());
-      }
-      if (geometry_set.has_instances()) {
-        GeometrySet::propagate_attributes_from_layer_to_instances(
-            geometry_set.get_grease_pencil()->attributes(),
-            geometry_set.get_instances_for_write()->attributes_for_write(),
-            attribute_filter);
+        GeometrySet temp_set = GeometrySet::from_instances(layer_instances);
+        const int handle = instances->add_reference(bke::InstanceReference{temp_set});
+        instances->add_instance(handle, float4x4::identity());
       }
+      GeometrySet::propagate_attributes_from_layer_to_instances(
+          geometry_set.get_grease_pencil()->attributes(),
+          instances->attributes_for_write(),
+          attribute_filter);
+      GeometrySet new_instances = geometry::join_geometries(
+          {GeometrySet::from_instances(dst_instances, bke::GeometryOwnershipType::Editable),
+           GeometrySet::from_instances(instances)},
+          attribute_filter);
+      instances_component.replace(
+          new_instances.get_component_for_write<InstancesComponent>().release());
+
       geometry_set.replace_grease_pencil(nullptr);
     }
     geometry_set.remove_geometry_during_modify();