Nodes: Fix drag link from output to already linked Multi-Input Socket

This patch fixes a visual bug related to connecting an output socket to
a Multi-Input Socket, that already has a link to that same output.
In this case, the drag link got a new index and snapped to a new
position. This path makes the drag link snap to the same position as the
first link between the two sockets.

Differential Revision: https://developer.blender.org/D10689

2 files changed, 20 insertions, 2 deletions

diff --git a/source/blender/editors/space_node/node_draw.cc b/source/blender/editors/space_node/node_draw.cc
index bb0cd754c7b..f64ce771b25 100644
--- a/source/blender/editors/space_node/node_draw.cc
+++ b/source/blender/editors/space_node/node_draw.cc
@@ -37,6 +37,7 @@
 #include "BLI_blenlib.h"
 #include "BLI_map.hh"
 #include "BLI_math.h"
+#include "BLI_set.hh"
 #include "BLI_span.hh"
 #include "BLI_string_ref.hh"
 #include "BLI_vector.hh"
@@ -81,6 +82,7 @@
 #  include "COM_compositor.h"
 #endif
 
+using blender::Set;
 using blender::Span;
 using blender::Vector;
 
@@ -1746,10 +1748,11 @@ static void count_mutli_input_socket_links(bNodeTree *ntree, SpaceNode *snode)
   LISTBASE_FOREACH (bNode *, node, &ntree->nodes) {
     LISTBASE_FOREACH (struct bNodeSocket *, socket, &node->inputs) {
       if (socket->flag & SOCK_MULTI_INPUT) {
+        Set<bNodeSocket *> visited_from_sockets;
         socket->total_inputs = 0;
         LISTBASE_FOREACH (bNodeLink *, link, &ntree->links) {
           if (link->tosock == socket) {
-            socket->total_inputs++;
+            visited_from_sockets.add(link->fromsock);
           }
         }
         /* Count temporary links going into this socket. */
@@ -1757,10 +1760,11 @@ static void count_mutli_input_socket_links(bNodeTree *ntree, SpaceNode *snode)
           LISTBASE_FOREACH (LinkData *, linkdata, &nldrag->links) {
             bNodeLink *link = (bNodeLink *)linkdata->data;
             if (link->tosock == socket) {
-              socket->total_inputs++;
+              visited_from_sockets.add(link->fromsock);
             }
           }
         }
+        socket->total_inputs = visited_from_sockets.size();
       }
     }
   }
diff --git a/source/blender/editors/space_node/node_relationships.c b/source/blender/editors/space_node/node_relationships.c
index 963349f876b..9293494a16a 100644
--- a/source/blender/editors/space_node/node_relationships.c
+++ b/source/blender/editors/space_node/node_relationships.c
@@ -890,10 +890,24 @@ static void node_link_find_socket(bContext *C, wmOperator *op, float cursor[2])
           continue;
         }
 
+        /* Skip if tsock is already linked with this output. */
+        bNodeLink *existing_link_connected_to_fromsock = NULL;
+        LISTBASE_FOREACH (bNodeLink *, existing_link, &snode->edittree->links) {
+          if (existing_link->fromsock == link->fromsock && existing_link->tosock == tsock) {
+            existing_link_connected_to_fromsock = existing_link;
+            break;
+          }
+        }
+
         /* attach links to the socket */
         link->tonode = tnode;
         link->tosock = tsock;
         snode->runtime->last_node_hovered_while_dragging_a_link = tnode;
+        if (existing_link_connected_to_fromsock) {
+          link->multi_input_socket_index =
+              existing_link_connected_to_fromsock->multi_input_socket_index;
+          continue;
+        }
         sort_multi_input_socket_links(snode, tnode, link, cursor);
       }
     }