Geometry Nodes: Run nodes once on unique instance data

As described in T91672, often it can be much more efficient to run each
node only on the unique geometry of the instances, rather than realizing
all instances and potentially processing redundant data. Sometimes the
performance difference can be completely smooth vs. completely unusable.

Geometry nodes used to hide that choice from users by always realizing
instances, but recently we have decided to expose it. So this commit
makes nodes run once per unique reference in the entire tree of nested
instances in their input geometries, continuing the work started in
rB0559971ab377 and rBf94164d89629f0d2. For the old behavior, a realize
instances node can be added before the nodes, which is done in the
versioning code.

Differential Revision: https://developer.blender.org/D12656

1 files changed, 75 insertions, 0 deletions

diff --git a/source/blender/blenloader/intern/versioning_300.c b/source/blender/blenloader/intern/versioning_300.c
index 86755cbaf95..3b51e40c218 100644
--- a/source/blender/blenloader/intern/versioning_300.c
+++ b/source/blender/blenloader/intern/versioning_300.c
@@ -449,6 +449,73 @@ static void do_versions_sequencer_speed_effect_recursive(Scene *scene, const Lis
 #undef SEQ_SPEED_COMPRESS_IPO_Y
 }
 
+static bNodeLink *find_connected_link(bNodeTree *ntree, bNodeSocket *in_socket)
+{
+  LISTBASE_FOREACH (bNodeLink *, link, &ntree->links) {
+    if (link->tosock == in_socket) {
+      return link;
+    }
+  }
+  return NULL;
+}
+
+static void add_realize_instances_before_socket(bNodeTree *ntree,
+                                                bNode *node,
+                                                bNodeSocket *geometry_socket)
+{
+  BLI_assert(geometry_socket->type == SOCK_GEOMETRY);
+  bNodeLink *link = find_connected_link(ntree, geometry_socket);
+  if (link == NULL) {
+    return;
+  }
+
+  /* If the realize instances node is already before this socket, no need to continue. */
+  if (link->fromnode->type == GEO_NODE_REALIZE_INSTANCES) {
+    return;
+  }
+
+  bNode *realize_node = nodeAddStaticNode(NULL, ntree, GEO_NODE_REALIZE_INSTANCES);
+  realize_node->parent = node->parent;
+  realize_node->locx = node->locx - 100;
+  realize_node->locy = node->locy;
+  nodeAddLink(ntree, link->fromnode, link->fromsock, realize_node, realize_node->inputs.first);
+  link->fromnode = realize_node;
+  link->fromsock = realize_node->outputs.first;
+}
+
+/**
+ * If a node used to realize instances implicitly and will no longer do so in 3.0, add a "Realize
+ * Instances" node in front of it to avoid changing behavior. Don't do this if the node will be
+ * replaced anyway though.
+ */
+static void version_geometry_nodes_add_realize_instance_nodes(bNodeTree *ntree)
+{
+  LISTBASE_FOREACH_MUTABLE (bNode *, node, &ntree->nodes) {
+    if (ELEM(node->type,
+             GEO_NODE_ATTRIBUTE_CAPTURE,
+             GEO_NODE_SEPARATE_COMPONENTS,
+             GEO_NODE_CONVEX_HULL,
+             GEO_NODE_CURVE_LENGTH,
+             GEO_NODE_BOOLEAN,
+             GEO_NODE_CURVE_FILLET,
+             GEO_NODE_CURVE_RESAMPLE,
+             GEO_NODE_CURVE_TO_MESH,
+             GEO_NODE_CURVE_TRIM,
+             GEO_NODE_MATERIAL_REPLACE,
+             GEO_NODE_MESH_SUBDIVIDE,
+             GEO_NODE_ATTRIBUTE_REMOVE,
+             GEO_NODE_TRIANGULATE)) {
+      bNodeSocket *geometry_socket = node->inputs.first;
+      add_realize_instances_before_socket(ntree, node, geometry_socket);
+    }
+    /* Also realize instances for the profile input of the curve to mesh node. */
+    if (node->type == GEO_NODE_CURVE_TO_MESH) {
+      bNodeSocket *profile_socket = node->inputs.last;
+      add_realize_instances_before_socket(ntree, node, profile_socket);
+    }
+  }
+}
+
 void do_versions_after_linking_300(Main *bmain, ReportList *UNUSED(reports))
 {
   if (MAIN_VERSION_ATLEAST(bmain, 300, 0) && !MAIN_VERSION_ATLEAST(bmain, 300, 1)) {
@@ -531,6 +598,14 @@ void do_versions_after_linking_300(Main *bmain, ReportList *UNUSED(reports))
     }
   }
 
+  if (!MAIN_VERSION_ATLEAST(bmain, 300, 28)) {
+    LISTBASE_FOREACH (bNodeTree *, ntree, &bmain->nodetrees) {
+      if (ntree->type == NTREE_GEOMETRY) {
+        version_geometry_nodes_add_realize_instance_nodes(ntree);
+      }
+    }
+  }
+
   /**
    * Versioning code until next subversion bump goes here.
    *