Geometry Nodes: Only create instance IDs when they exist

Instance IDs serve no purpose for rendering when they aren't stable from
one frame to the next, and if the index is used in the end anyway, there
is no point in storing a vector of IDs and copying it around.

This commit exposes the `id` attribute on the instances component,
makes it optional-- only generated by default with the distribute points
on faces node.

Since the string to curves node only added the index as each instance's
ID, I removed it. This means that it would be necessary to add the ID
data manually if the initial index actually helps (when deleting only
certain characters, for example).

Differential Revision: https://developer.blender.org/D12980

5 files changed, 22 insertions, 15 deletions

diff --git a/source/blender/nodes/geometry/nodes/legacy/node_geo_point_instance.cc b/source/blender/nodes/geometry/nodes/legacy/node_geo_point_instance.cc
index fb45c22ced4..b68dfe44984 100644
--- a/source/blender/nodes/geometry/nodes/legacy/node_geo_point_instance.cc
+++ b/source/blender/nodes/geometry/nodes/legacy/node_geo_point_instance.cc
@@ -184,7 +184,7 @@ static void add_instances_from_component(InstancesComponent &instances,
   instances.resize(start_len + domain_size);
   MutableSpan<int> handles = instances.instance_reference_handles().slice(start_len, domain_size);
   MutableSpan<float4x4> transforms = instances.instance_transforms().slice(start_len, domain_size);
-  MutableSpan<int> instance_ids = instances.instance_ids().slice(start_len, domain_size);
+  MutableSpan<int> instance_ids = instances.instance_ids_ensure().slice(start_len, domain_size);
 
   /* Skip all of the randomness handling if there is only a single possible instance
    * (anything except for collection mode with "Whole Collection" turned off). */
diff --git a/source/blender/nodes/geometry/nodes/node_geo_instance_on_points.cc b/source/blender/nodes/geometry/nodes/node_geo_instance_on_points.cc
index 44cad2d38d4..f4a127faf43 100644
--- a/source/blender/nodes/geometry/nodes/node_geo_instance_on_points.cc
+++ b/source/blender/nodes/geometry/nodes/node_geo_instance_on_points.cc
@@ -77,7 +77,6 @@ static void add_instances_from_component(InstancesComponent &dst_component,
                                                                                   select_len);
   MutableSpan<float4x4> dst_transforms = dst_component.instance_transforms().slice(start_len,
                                                                                    select_len);
-  MutableSpan<int> dst_stable_ids = dst_component.instance_ids().slice(start_len, select_len);
 
   FieldEvaluator field_evaluator{field_context, domain_size};
   const VArray<bool> *pick_instance = nullptr;
@@ -86,7 +85,6 @@ static void add_instances_from_component(InstancesComponent &dst_component,
   const VArray<float3> *scales = nullptr;
   /* The evaluator could use the component's stable IDs as a destination directly, but only the
    * selected indices should be copied. */
-  GVArray_Typed<int> stable_ids = src_component.attribute_get_for_read("id", ATTR_DOMAIN_POINT, 0);
   field_evaluator.add(params.get_input<Field<bool>>("Pick Instance"), &pick_instance);
   field_evaluator.add(params.get_input<Field<int>>("Instance Index"), &indices);
   field_evaluator.add(params.get_input<Field<float3>>("Rotation"), &rotations);
@@ -119,7 +117,6 @@ static void add_instances_from_component(InstancesComponent &dst_component,
   threading::parallel_for(selection.index_range(), 1024, [&](IndexRange selection_range) {
     for (const int range_i : selection_range) {
       const int64_t i = selection[range_i];
-      dst_stable_ids[range_i] = (*stable_ids)[i];
 
       /* Compute base transform for every instances. */
       float4x4 &dst_transform = dst_transforms[range_i];
@@ -157,6 +154,17 @@ static void add_instances_from_component(InstancesComponent &dst_component,
     }
   });
 
+  GVArrayPtr id_attribute = src_component.attribute_try_get_for_read(
+      "id", ATTR_DOMAIN_POINT, CD_PROP_INT32);
+  if (id_attribute) {
+    GVArray_Typed<int> ids{*id_attribute};
+    VArray_Span<int> ids_span{ids};
+    MutableSpan<int> dst_ids = dst_component.instance_ids_ensure();
+    for (const int64_t i : selection.index_range()) {
+      dst_ids[i] = ids_span[selection[i]];
+    }
+  }
+
   if (pick_instance->is_single()) {
     if (pick_instance->get_internal_single()) {
       if (instance.has_realized_data()) {
diff --git a/source/blender/nodes/geometry/nodes/node_geo_instances_to_points.cc b/source/blender/nodes/geometry/nodes/node_geo_instances_to_points.cc
index 63d1f88a442..434fe4a19d7 100644
--- a/source/blender/nodes/geometry/nodes/node_geo_instances_to_points.cc
+++ b/source/blender/nodes/geometry/nodes/node_geo_instances_to_points.cc
@@ -77,13 +77,15 @@ static void convert_instances_to_points(GeometrySet &geometry_set,
   const VArray<float> &radii = evaluator.get_evaluated<float>(1);
   copy_attribute_to_points(radii, selection, {pointcloud->radius, pointcloud->totpoint});
 
-  OutputAttribute_Typed<int> id_attribute = points.attribute_try_get_for_output<int>(
-      "id", ATTR_DOMAIN_POINT, 0);
-  MutableSpan<int> ids = id_attribute.as_span();
-  for (const int i : selection.index_range()) {
-    ids[i] = instances.instance_ids()[selection[i]];
+  if (!instances.instance_ids().is_empty()) {
+    OutputAttribute_Typed<int> id_attribute = points.attribute_try_get_for_output<int>(
+        "id", ATTR_DOMAIN_POINT, CD_PROP_INT32);
+    MutableSpan<int> ids = id_attribute.as_span();
+    for (const int i : selection.index_range()) {
+      ids[i] = instances.instance_ids()[selection[i]];
+    }
+    id_attribute.save();
   }
-  id_attribute.save();
 }
 
 static void geo_node_instances_to_points_exec(GeoNodeExecParams params)
diff --git a/source/blender/nodes/geometry/nodes/node_geo_join_geometry.cc b/source/blender/nodes/geometry/nodes/node_geo_join_geometry.cc
index b628c5cbab8..bbba8635b88 100644
--- a/source/blender/nodes/geometry/nodes/node_geo_join_geometry.cc
+++ b/source/blender/nodes/geometry/nodes/node_geo_join_geometry.cc
@@ -270,17 +270,16 @@ static void join_components(Span<const InstancesComponent *> src_components, Geo
     }
 
     Span<float4x4> src_transforms = src_component->instance_transforms();
-    Span<int> src_ids = src_component->instance_ids();
     Span<int> src_reference_handles = src_component->instance_reference_handles();
 
     for (const int i : src_transforms.index_range()) {
       const int src_handle = src_reference_handles[i];
       const int dst_handle = handle_map[src_handle];
       const float4x4 &transform = src_transforms[i];
-      const int id = src_ids[i];
-      dst_component.add_instance(dst_handle, transform, id);
+      dst_component.add_instance(dst_handle, transform);
     }
   }
+  join_attributes(to_base_components(src_components), dst_component, {"position"});
 }
 
 static void join_components(Span<const VolumeComponent *> src_components, GeometrySet &result)
diff --git a/source/blender/nodes/geometry/nodes/node_geo_string_to_curves.cc b/source/blender/nodes/geometry/nodes/node_geo_string_to_curves.cc
index ac946540221..83526df3ac2 100644
--- a/source/blender/nodes/geometry/nodes/node_geo_string_to_curves.cc
+++ b/source/blender/nodes/geometry/nodes/node_geo_string_to_curves.cc
@@ -242,13 +242,11 @@ static void add_instances_from_handles(InstancesComponent &instances,
   instances.resize(positions.size());
   MutableSpan<int> handles = instances.instance_reference_handles();
   MutableSpan<float4x4> transforms = instances.instance_transforms();
-  MutableSpan<int> instance_ids = instances.instance_ids();
 
   threading::parallel_for(IndexRange(positions.size()), 256, [&](IndexRange range) {
     for (const int i : range) {
       handles[i] = char_handles.lookup(charcodes[i]);
       transforms[i] = float4x4::from_location({positions[i].x, positions[i].y, 0});
-      instance_ids[i] = i;
     }
   });
 }