Node callback for handling link insertion and swapping of occupied inputs.

Nodes have a feature for moving existing links to unoccupied sockets when connecting
to an already used input. This is based on the standard legacy socket types (value/float,
vector, color/rgba) and works reasonably well for shader, compositor and texture nodes.

For new pynode systems, however, the hardcoded nature of that feature has major drawbacks:
* It does not take different type systems into account, leading to meaningless connections
  when sockets are swapped and making the feature useless or outright debilitating.
* Advanced socket behaviors would be possible with a registerable callback, e.g. creating
  extensible input lists that move existing connections down to make room for a new link.

Now any handling of new links is done via the 'insert_links' callback, which can also be
registered through the RNA API. For the legacy shader/compo/tex nodes the behavior is the
same, using a C callback.

Note on the 'use_swap' flag: this has been removed because it was meaningless anyway:
It was disabled only for the insert-node-on-link feature, which works only for
completely unconnected nodes anyway, so there would be nothing to swap in the first place.

1 files changed, 3 insertions, 0 deletions

diff --git a/source/blender/nodes/intern/node_util.h b/source/blender/nodes/intern/node_util.h
index 64b2028874b..2e20a8e79d4 100644
--- a/source/blender/nodes/intern/node_util.h
+++ b/source/blender/nodes/intern/node_util.h
@@ -76,6 +76,9 @@ void node_math_label(struct bNodeTree *ntree, struct bNode *node, char *label, i
 void node_vect_math_label(struct bNodeTree *ntree, struct bNode *node, char *label, int maxlen);
 void node_filter_label(struct bNodeTree *ntree, struct bNode *node, char *label, int maxlen);
 
+
+/*** Link Handling */
+void node_insert_link_default(struct bNodeTree *ntree, struct bNode *node, struct bNodeLink *link);
 void node_update_internal_links_default(struct bNodeTree *ntree, struct bNode *node);
 
 float node_socket_get_float(struct bNodeTree *ntree, struct bNode *node, struct bNodeSocket *sock);