Geometry Nodes: new evaluation system

This refactors the geometry nodes evaluation system. No changes for the
user are expected. At a high level the goals are:
* Support using geometry nodes outside of the geometry nodes modifier.
* Support using the evaluator infrastructure for other purposes like field evaluation.
* Support more nodes, especially when many of them are disabled behind switch nodes.
* Support doing preprocessing on node groups.

For more details see T98492.

There are fairly detailed comments in the code, but here is a high level overview
for how it works now:
* There is a new "lazy-function" system. It is similar in spirit to the multi-function
  system but with different goals. Instead of optimizing throughput for highly
  parallelizable work, this system is designed to compute only the data that is actually
  necessary. What data is necessary can be determined dynamically during evaluation.
  Many lazy-functions can be composed in a graph to form a new lazy-function, which can
  again be used in a graph etc.
* Each geometry node group is converted into a lazy-function graph prior to evaluation.
  To evaluate geometry nodes, one then just has to evaluate that graph. Node groups are
  no longer inlined into their parents.

Next steps for the evaluation system is to reduce the use of threads in some situations
to avoid overhead. Many small node groups don't benefit from multi-threading at all.
This is much easier to do now because not everything has to be inlined in one huge
node tree anymore.

Differential Revision: https://developer.blender.org/D15914

1 files changed, 29 insertions, 1 deletions

diff --git a/source/blender/blenkernel/BKE_node_runtime.hh b/source/blender/blenkernel/BKE_node_runtime.hh
index f2e551a9f32..194820aa4ba 100644
--- a/source/blender/blenkernel/BKE_node_runtime.hh
+++ b/source/blender/blenkernel/BKE_node_runtime.hh
@@ -21,6 +21,7 @@ struct bNodeType;
 namespace blender::nodes {
 struct FieldInferencingInterface;
 class NodeDeclaration;
+struct GeometryNodesLazyFunctionGraphInfo;
 }  // namespace blender::nodes
 
 namespace blender::bke {
@@ -49,6 +50,15 @@ class bNodeTreeRuntime : NonCopyable, NonMovable {
   std::unique_ptr<nodes::FieldInferencingInterface> field_inferencing_interface;
 
   /**
+   * For geometry nodes, a lazy function graph with some additional info is cached. This is used to
+   * evaluate the node group. Caching it here allows us to reuse the preprocessed node tree in case
+   * its used multiple times.
+   */
+  std::mutex geometry_nodes_lazy_function_graph_info_mutex;
+  std::unique_ptr<nodes::GeometryNodesLazyFunctionGraphInfo>
+      geometry_nodes_lazy_function_graph_info;
+
+  /**
    * Protects access to all topology cache variables below. This is necessary so that the cache can
    * be updated on a const #bNodeTree.
    */
@@ -70,6 +80,7 @@ class bNodeTreeRuntime : NonCopyable, NonMovable {
   MultiValueMap<const bNodeType *, bNode *> nodes_by_type;
   Vector<bNode *> toposort_left_to_right;
   Vector<bNode *> toposort_right_to_left;
+  Vector<bNode *> group_nodes;
   bool has_link_cycle = false;
   bool has_undefined_nodes_or_sockets = false;
   bNode *group_output_node = nullptr;
@@ -148,6 +159,12 @@ class bNodeRuntime : NonCopyable, NonMovable {
 
 namespace node_tree_runtime {
 
+/**
+ * Is executed when the depsgraph determines that something in the node group changed that will
+ * affect the output.
+ */
+void handle_node_tree_output_changed(bNodeTree &tree_cow);
+
 class AllowUsingOutdatedInfo : NonCopyable, NonMovable {
  private:
   const bNodeTree &tree_;
@@ -241,6 +258,18 @@ inline blender::Span<bNode *> bNodeTree::all_nodes()
   return this->runtime->nodes;
 }
 
+inline blender::Span<const bNode *> bNodeTree::group_nodes() const
+{
+  BLI_assert(blender::bke::node_tree_runtime::topology_cache_is_available(*this));
+  return this->runtime->group_nodes;
+}
+
+inline blender::Span<bNode *> bNodeTree::group_nodes()
+{
+  BLI_assert(blender::bke::node_tree_runtime::topology_cache_is_available(*this));
+  return this->runtime->group_nodes;
+}
+
 inline bool bNodeTree::has_link_cycle() const
 {
   BLI_assert(blender::bke::node_tree_runtime::topology_cache_is_available(*this));
@@ -413,7 +442,6 @@ inline blender::Span<const bNodeLink *> bNode::internal_links_span() const
 
 inline const blender::nodes::NodeDeclaration *bNode::declaration() const
 {
-  BLI_assert(this->runtime->declaration != nullptr);
   return this->runtime->declaration;
 }