Eevee: Fix nodegroup sockets behaviour

Node group inputs should behave like cycles now.

----

We create dummy nodes that contains the default values for the nodegroup
inputs and link them to the sockets. This way the uniform buffer gathering
function can read them.

But we also need to disconnect all the internal links to sockets that have
hidden values. Theses sockets must not get the values from the nodegroup
input sockets if there is no link to them otherwise we get broken results
(i.e.: normals for a bsdf node).

source/blender/gpu/intern/gpu_codegen.c

@@ -1409,19 +1409,11 @@ static GPUNodeLink *gpu_uniformbuffer_link(
 {
 	bNodeSocket *socket;
 
-	/* Some nodes can have been create on the fly and does
-	 * not have an original to point to. (i.e. the bump from
-	 * ntree_shader_relink_displacement). In this case just
-	 * revert to static constant folding. */
-	if (node->original == NULL) {
-		return NULL;
-	}
-
 	if (in_out == SOCK_IN) {
-		socket = BLI_findlink(&node->original->inputs, index);
+		socket = BLI_findlink(&node->inputs, index);
 	}
 	else {
-		socket = BLI_findlink(&node->original->outputs, index);
+		socket = BLI_findlink(&node->outputs, index);
 	}
 
 	BLI_assert(socket != NULL);

source/blender/nodes/shader/node_shader_tree.c

@@ -283,6 +283,90 @@ static bNodeSocket *ntree_shader_node_find_output(bNode *node,
 	return ntree_shader_node_find_socket(&node->outputs, identifier);
 }
 
+static void ntree_shader_unlink_hidden_value_sockets(bNode *group_node, bNodeSocket *isock)
+{
+	bNodeTree *group_ntree = (bNodeTree *)group_node->id;
+	bNode *node;
+	bool removed_link = false;
+
+	for (node = group_ntree->nodes.first; node; node = node->next) {
+		for (bNodeSocket *sock = node->inputs.first; sock; sock = sock->next) {
+			if ((sock->flag & SOCK_HIDE_VALUE) == 0)
+				continue;
+			/* If socket is linked to a group input node and sockets id match. */
+			if (sock && sock->link && sock->link->fromnode->type == NODE_GROUP_INPUT) {
+				if (STREQ(isock->identifier, sock->link->fromsock->identifier)) {
+					nodeRemLink(group_ntree, sock->link);
+					removed_link = true;
+				}
+			}
+		}
+	}
+
+	if (removed_link) {
+		ntreeUpdateTree(G.main, group_ntree);
+	}
+}
+
+/* Node groups once expanded looses their input sockets values.
+ * To fix this, link value/rgba nodes into the sockets and copy the group sockets values. */
+static void ntree_shader_groups_expand_inputs(bNodeTree *localtree)
+{
+	bNode *value_node, *group_node;
+	bNodeSocket *value_socket;
+	bNodeSocketValueRGBA *src_rgba, *dst_rgba;
+	bNodeSocketValueFloat *src_float, *dst_float;
+	bool link_added = false;
+
+	for (group_node = localtree->nodes.first; group_node; group_node = group_node->next) {
+
+		if (group_node->type != NODE_GROUP || group_node->id == NULL)
+			continue;
+
+		bNodeSocket *group_socket = group_node->inputs.first;
+		for (; group_socket; group_socket = group_socket->next) {
+			if (group_socket->link != NULL)
+				continue;
+
+			/* Detect the case where an input is plugged into a hidden value socket.
+			 * In this case we should just remove the link to trigger the socket default override. */
+			ntree_shader_unlink_hidden_value_sockets(group_node, group_socket);
+
+			switch (group_socket->type) {
+				case SOCK_VECTOR:
+				case SOCK_RGBA:
+					value_node = nodeAddStaticNode(NULL, localtree, SH_NODE_RGB);
+					value_socket = ntree_shader_node_find_output(value_node, "Color");
+					BLI_assert(value_socket != NULL);
+					src_rgba = group_socket->default_value;
+					dst_rgba = value_socket->default_value;
+					copy_v4_v4(dst_rgba->value, src_rgba->value);
+					break;
+				case SOCK_FLOAT:
+					value_node = nodeAddStaticNode(NULL, localtree, SH_NODE_VALUE);
+					value_socket = ntree_shader_node_find_output(value_node, "Value");
+					BLI_assert(value_socket != NULL);
+					src_float = group_socket->default_value;
+					dst_float = value_socket->default_value;
+					dst_float->value = src_float->value;
+					break;
+				default:
+					continue;
+			}
+
+			nodeAddLink(localtree,
+			            value_node, value_socket,
+			            group_node, group_socket);
+
+			link_added = true;
+		}
+	}
+
+	if (link_added) {
+		ntreeUpdateTree(G.main, localtree);
+	}
+}
+
 /* Check whether shader has a displacement.
  *
  * Will also return a node and it's socket which is connected to a displacement
@@ -589,6 +673,8 @@ void ntreeGPUMaterialNodes(bNodeTree *localtree, GPUMaterial *mat, bool *has_sur
 	bNode *output = ntreeShaderOutputNode(localtree, SHD_OUTPUT_EEVEE);
 	bNodeTreeExec *exec;
 
+	ntree_shader_groups_expand_inputs(localtree);
+
 	/* Perform all needed modifications on the tree in order to support
 	 * displacement/bump mapping.
 	 */