Add GraphEdit.is_node_hover_valid(...) method

This is a virtual method that can be used to add additional error
condition checks while the connection is still being dragged. If true is
returned, the connection is valid. If false is returned, the connection
is invalid and thus not possible (ie. it will not snap). The virtual
method is exposed with an underscore to scripts.

2 files changed, 17 insertions, 0 deletions

diff --git a/scene/gui/graph_edit.cpp b/scene/gui/graph_edit.cpp
index f51031765c..42f434f0ac 100644
--- a/scene/gui/graph_edit.cpp
+++ b/scene/gui/graph_edit.cpp
@@ -710,6 +710,9 @@ void GraphEdit::_top_layer_input(const Ref<InputEvent> &p_ev) {
 
 						int type = gn->get_connection_output_type(j);
 						if ((type == connecting_type || valid_connection_types.has(ConnType(connecting_type, type))) && is_in_output_hotzone(gn, j, mpos, port_size)) {
+							if (!is_node_hover_valid(gn->get_name(), j, connecting_from, connecting_index)) {
+								continue;
+							}
 							connecting_target = true;
 							connecting_to = pos;
 							connecting_target_to = gn->get_name();
@@ -725,6 +728,9 @@ void GraphEdit::_top_layer_input(const Ref<InputEvent> &p_ev) {
 
 						int type = gn->get_connection_input_type(j);
 						if ((type == connecting_type || valid_connection_types.has(ConnType(connecting_type, type))) && is_in_input_hotzone(gn, j, mpos, port_size)) {
+							if (!is_node_hover_valid(connecting_from, connecting_index, gn->get_name(), j)) {
+								continue;
+							}
 							connecting_target = true;
 							connecting_to = pos;
 							connecting_target_to = gn->get_name();
@@ -1453,6 +1459,14 @@ void GraphEdit::force_connection_drag_end() {
 	emit_signal(SNAME("connection_drag_ended"));
 }
 
+bool GraphEdit::is_node_hover_valid(const StringName &p_from, const int p_from_port, const StringName &p_to, const int p_to_port) {
+	bool valid;
+	if (GDVIRTUAL_CALL(_is_node_hover_valid, p_from, p_from_port, p_to, p_to_port, valid)) {
+		return valid;
+	}
+	return true;
+}
+
 void GraphEdit::set_panning_scheme(PanningScheme p_scheme) {
 	panning_scheme = p_scheme;
 	panner->set_control_scheme((ViewPanner::ControlScheme)p_scheme);
@@ -2315,6 +2329,7 @@ void GraphEdit::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_selected", "node"), &GraphEdit::set_selected);
 
 	GDVIRTUAL_BIND(_get_connection_line, "from", "to")
+	GDVIRTUAL_BIND(_is_node_hover_valid, "from", "from_slot", "to", "to_slot");
 
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "right_disconnects"), "set_right_disconnects", "is_right_disconnects_enabled");
 	ADD_PROPERTY(PropertyInfo(Variant::VECTOR2, "scroll_offset", PROPERTY_HINT_NONE, "suffix:px"), "set_scroll_ofs", "get_scroll_ofs");
diff --git a/scene/gui/graph_edit.h b/scene/gui/graph_edit.h
index beb17ec4cf..cf35aeb8b2 100644
--- a/scene/gui/graph_edit.h
+++ b/scene/gui/graph_edit.h
@@ -280,6 +280,7 @@ protected:
 	GDVIRTUAL2RC(Vector<Vector2>, _get_connection_line, Vector2, Vector2)
 	GDVIRTUAL3R(bool, _is_in_input_hotzone, Object *, int, Vector2)
 	GDVIRTUAL3R(bool, _is_in_output_hotzone, Object *, int, Vector2)
+	GDVIRTUAL4R(bool, _is_node_hover_valid, StringName, int, StringName, int);
 
 public:
 	Error connect_node(const StringName &p_from, int p_from_port, const StringName &p_to, int p_to_port);
@@ -287,6 +288,7 @@ public:
 	void disconnect_node(const StringName &p_from, int p_from_port, const StringName &p_to, int p_to_port);
 	void clear_connections();
 	void force_connection_drag_end();
+	virtual bool is_node_hover_valid(const StringName &p_from, int p_from_port, const StringName &p_to, int p_to_port);
 
 	void set_connection_activity(const StringName &p_from, int p_from_port, const StringName &p_to, int p_to_port, float p_activity);