Node Editor: Link Drag Search Menu

This commit adds a search menu when links are dragged above empty
space. When releasing the drag, a menu displays all compatible
sockets with the source link. The "main" sockets (usually the first)
are weighted above other sockets in the search, so they appear first
when you type the name of the node.

A few special operators for creating a reroute or a group input node
are also added to the search.

Translation is started after choosing a node so it can be placed
quickly, since users would likely adjust the position after anyway.

A small "+" is displayed next to the cursor to give a hint about this.

Further improvements are possible after this first iteration:
 - Support custom node trees.
 - Better drawing of items in the search menu.
 - Potential tweaks to filtering of items, depending on user feedback.

Thanks to Juanfran Matheu for developing an initial patch.

Differential Revision: https://developer.blender.org/D8286

1 files changed, 31 insertions, 2 deletions

diff --git a/source/blender/blenkernel/BKE_node.h b/source/blender/blenkernel/BKE_node.h
index 2038842ee59..a2959556810 100644
--- a/source/blender/blenkernel/BKE_node.h
+++ b/source/blender/blenkernel/BKE_node.h
@@ -34,6 +34,10 @@
 #include "RNA_types.h"
 
 #ifdef __cplusplus
+#  include "BLI_string_ref.hh"
+#endif
+
+#ifdef __cplusplus
 extern "C" {
 #endif
 
@@ -114,6 +118,7 @@ namespace nodes {
 class NodeMultiFunctionBuilder;
 class GeoNodeExecParams;
 class NodeDeclarationBuilder;
+class GatherLinkSearchOpParams;
 }  // namespace nodes
 namespace fn {
 class CPPType;
@@ -129,10 +134,15 @@ using SocketGetCPPValueFunction = void (*)(const struct bNodeSocket &socket, voi
 using SocketGetGeometryNodesCPPValueFunction = void (*)(const struct bNodeSocket &socket,
                                                         void *r_value);
 
+/* Adds socket link operations that are specific to this node type. */
+using NodeGatherSocketLinkOperationsFunction =
+    void (*)(blender::nodes::GatherLinkSearchOpParams &params);
+
 #else
 typedef void *NodeMultiFunctionBuildFunction;
 typedef void *NodeGeometryExecFunction;
 typedef void *NodeDeclareFunction;
+typedef void *NodeGatherSocketLinkOperationsFunction;
 typedef void *SocketGetCPPTypeFunction;
 typedef void *SocketGetGeometryNodesCPPTypeFunction;
 typedef void *SocketGetGeometryNodesCPPValueFunction;
@@ -284,7 +294,7 @@ typedef struct bNodeType {
 
   /**
    * Can this node type be added to a node tree?
-   * \param r_disabled_hint: Optional hint to display in the UI when the poll fails.
+   * \param r_disabled_hint: Hint to display in the UI when the poll fails.
    *                         The callback can set this to a static string without having to
    *                         null-check it (or without setting it to null if it's not used).
    *                         The caller must pass a valid `const char **` and null-initialize it
@@ -325,6 +335,13 @@ typedef struct bNodeType {
   /* Declaration to be used when it is not dynamic. */
   NodeDeclarationHandle *fixed_declaration;
 
+  /**
+   * Add to the list of search names and operations gathered by node link drag searching.
+   * Usually it isn't necessary to override the default behavior here, but a node type can have
+   * custom behavior here like adding custom search items.
+   */
+  NodeGatherSocketLinkOperationsFunction gather_link_search_ops;
+
   /** True when the node cannot be muted. */
   bool no_muting;
 
@@ -402,7 +419,7 @@ typedef struct bNodeTreeType {
   /* Tree update. Overrides `nodetype->updatetreefunc` ! */
   void (*update)(struct bNodeTree *ntree);
 
-  bool (*validate_link)(struct bNodeTree *ntree, struct bNodeLink *link);
+  bool (*validate_link)(eNodeSocketDatatype from, eNodeSocketDatatype to);
 
   void (*node_add_init)(struct bNodeTree *ntree, struct bNode *bnode);
 
@@ -1768,6 +1785,18 @@ extern struct bNodeSocketType NodeSocketTypeUndefined;
 }
 #endif
 
+#ifdef __cplusplus
+
+namespace blender::bke {
+
+bNodeSocket *node_find_enabled_socket(bNode &node, eNodeSocketInOut in_out, StringRef name);
+bNodeSocket *node_find_enabled_input_socket(bNode &node, StringRef name);
+bNodeSocket *node_find_enabled_output_socket(bNode &node, StringRef name);
+
+}  // namespace blender::bke
+
+#endif
+
 #define NODE_STORAGE_FUNCS(StorageT) \
   [[maybe_unused]] static StorageT &node_storage(bNode &node) \
   { \