Implemented a very crude face creation algorithm. Also did the gui for it. I't not perfect, it does depend on the selection order if you have more than 3 vertices selected. I'll implement a better one later.

game/addons/mesh_data_resource_editor/MDIEd.gd

@@ -156,3 +156,6 @@ func _on_add_triangle_at_pressed():
 
 func _on_add_auad_at_pressed():
 	plugin.add_quad_at()
+
+func _oncreate_face_pressed():
+	plugin.create_face()

game/addons/mesh_data_resource_editor/MDIEd.tscn

@@ -181,7 +181,7 @@ margin_bottom = 94.0
 [node name="VertexOps" type="VBoxContainer" parent="VBoxContainer"]
 margin_top = 98.0
 margin_right = 1010.0
-margin_bottom = 208.0
+margin_bottom = 232.0
 
 [node name="OperationsLabel" type="Label" parent="VBoxContainer/VertexOps"]
 margin_right = 1010.0
@@ -193,29 +193,35 @@ valign = 1
 [node name="Operations" type="VBoxContainer" parent="VBoxContainer/VertexOps"]
 margin_top = 18.0
 margin_right = 1010.0
-margin_bottom = 110.0
+margin_bottom = 134.0
 
-[node name="Merge" type="Button" parent="VBoxContainer/VertexOps/Operations"]
+[node name="AddFace" type="Button" parent="VBoxContainer/VertexOps/Operations"]
 margin_right = 1010.0
 margin_bottom = 20.0
-text = "Merge"
+text = "Create Face"
 
-[node name="Split" type="Button" parent="VBoxContainer/VertexOps/Operations"]
+[node name="Merge" type="Button" parent="VBoxContainer/VertexOps/Operations"]
 margin_top = 24.0
 margin_right = 1010.0
 margin_bottom = 44.0
-text = "Split"
+text = "Merge"
 
-[node name="Connect" type="Button" parent="VBoxContainer/VertexOps/Operations"]
+[node name="Split" type="Button" parent="VBoxContainer/VertexOps/Operations"]
 margin_top = 48.0
 margin_right = 1010.0
 margin_bottom = 68.0
-text = "Connect"
+text = "Split"
 
-[node name="Disconnect" type="Button" parent="VBoxContainer/VertexOps/Operations"]
+[node name="Connect" type="Button" parent="VBoxContainer/VertexOps/Operations"]
 margin_top = 72.0
 margin_right = 1010.0
 margin_bottom = 92.0
+text = "Connect"
+
+[node name="Disconnect" type="Button" parent="VBoxContainer/VertexOps/Operations"]
+margin_top = 96.0
+margin_right = 1010.0
+margin_bottom = 116.0
 text = "Disconnect"
 
 [node name="EdgeOps" type="VBoxContainer" parent="VBoxContainer"]
@@ -307,9 +313,9 @@ margin_bottom = 92.0
 text = "Disconnect"
 
 [node name="Operations" type="VBoxContainer" parent="VBoxContainer"]
-margin_top = 212.0
+margin_top = 236.0
 margin_right = 1010.0
-margin_bottom = 322.0
+margin_bottom = 346.0
 
 [node name="OperationsLabel" type="Label" parent="VBoxContainer/Operations"]
 margin_right = 1010.0
@@ -347,14 +353,14 @@ margin_bottom = 92.0
 text = "Rem Doubles"
 
 [node name="HSeparator3" type="HSeparator" parent="VBoxContainer"]
-margin_top = 326.0
+margin_top = 350.0
 margin_right = 1010.0
-margin_bottom = 330.0
+margin_bottom = 354.0
 
 [node name="Add" type="VBoxContainer" parent="VBoxContainer"]
-margin_top = 334.0
+margin_top = 358.0
 margin_right = 1010.0
-margin_bottom = 420.0
+margin_bottom = 444.0
 
 [node name="AddLabel" type="Label" parent="VBoxContainer/Add"]
 margin_right = 1010.0
@@ -410,12 +416,12 @@ margin_bottom = 20.0
 text = "At"
 
 [node name="HSeparator2" type="HSeparator" parent="VBoxContainer"]
-margin_top = 424.0
+margin_top = 448.0
 margin_right = 1010.0
-margin_bottom = 428.0
+margin_bottom = 452.0
 
 [node name="VBoxContainer" type="VBoxContainer" parent="VBoxContainer"]
-margin_top = 432.0
+margin_top = 456.0
 margin_right = 1010.0
 margin_bottom = 586.0
 size_flags_horizontal = 3
@@ -431,7 +437,7 @@ valign = 1
 [node name="UVEditorScrollContainer" type="ScrollContainer" parent="VBoxContainer/VBoxContainer"]
 margin_top = 18.0
 margin_right = 1010.0
-margin_bottom = 154.0
+margin_bottom = 130.0
 size_flags_horizontal = 3
 size_flags_vertical = 3
 __meta__ = {
@@ -456,6 +462,7 @@ script = ExtResource( 3 )
 [connection signal="toggled" from="VBoxContainer/Actions/Actions/VBoxContainer2/HBoxContainer3/Edge" to="VBoxContainer/EdgeOps" method="set_visible"]
 [connection signal="toggled" from="VBoxContainer/Actions/Actions/VBoxContainer2/HBoxContainer3/Face" to="." method="on_selection_mode_face_toggled"]
 [connection signal="toggled" from="VBoxContainer/Actions/Actions/VBoxContainer2/HBoxContainer3/Face" to="VBoxContainer/FaceOps" method="set_visible"]
+[connection signal="pressed" from="VBoxContainer/VertexOps/Operations/AddFace" to="." method="_oncreate_face_pressed"]
 [connection signal="pressed" from="VBoxContainer/VertexOps/Operations/Merge" to="." method="_on_merge_pressed"]
 [connection signal="pressed" from="VBoxContainer/VertexOps/Operations/Split" to="." method="_on_split_pressed"]
 [connection signal="pressed" from="VBoxContainer/VertexOps/Operations/Connect" to="." method="_on_connect_pressed"]

game/addons/mesh_data_resource_editor/MIDGizmo.gd

@@ -31,6 +31,7 @@ var axis_constraint : int = AxisConstraint.X | AxisConstraint.Y | AxisConstraint
 var selection_mode : int = SelectionMode.SELECTION_MODE_VERTEX
 var previous_point : Vector2
 var is_dragging : bool = false
+var _last_known_camera_facing : Vector3 = Vector3(0, 0, -1)
 
 var _mdr : MeshDataResource = null
 
@@ -155,6 +156,8 @@ func apply() -> void:
 	_mdr.connect("changed", self, "on_mdr_changed")
 
 func forward_spatial_gui_input(index, camera, event):
+	_last_known_camera_facing = camera.transform.basis.xform(Vector3(0, 0, -1))
+	
 	if event is InputEventMouseButton:
 		var gt : Transform = get_spatial_node().global_transform
 		var ray_from : Vector3 = camera.global_transform.origin
@@ -635,3 +638,29 @@ func connect_action():
 
 func disconnect_action():
 	pass
+
+func create_face():
+	if !_mdr:
+		return
+		
+	if _selected_points.size() <= 2:
+		return
+		
+	var mdr_arr : Array = _mdr.array
+	
+	if mdr_arr.size() != ArrayMesh.ARRAY_MAX || mdr_arr[ArrayMesh.ARRAY_VERTEX] == null || mdr_arr[ArrayMesh.ARRAY_VERTEX].size() == 0:
+		return
+	
+	if selection_mode == SelectionMode.SELECTION_MODE_VERTEX:
+		
+		var points : PoolVector3Array = PoolVector3Array()
+		
+		for sp in _selected_points:
+			points.push_back(_handle_points[sp])
+			
+		MDRMeshUtils.add_triangulated_mesh_from_points(_mdr, points, _last_known_camera_facing)
+	
+	elif selection_mode == SelectionMode.SELECTION_MODE_EDGE:
+		pass
+	elif selection_mode == SelectionMode.SELECTION_MODE_FACE:
+		pass

game/addons/mesh_data_resource_editor/plugin.gd

@@ -205,3 +205,7 @@ func connect_action():
 func disconnect_action():
 	for g in active_gizmos:
 		g.disconnect_action()
+		
+func create_face():
+	for g in active_gizmos:
+		g.create_face()

game/addons/mesh_data_resource_editor/utilities/mdred_mesh_utils.gd

@@ -1,6 +1,45 @@
 tool
 extends Object
 
+static func add_triangulated_mesh_from_points(mdr : MeshDataResource, selected_points : PoolVector3Array, last_known_camera_facing : Vector3) -> void:
+	
+	if selected_points.size() < 3:
+		return
+	
+	var st : SurfaceTool = SurfaceTool.new()
+	
+	st.begin(Mesh.PRIMITIVE_TRIANGLES)
+
+	var v0 : Vector3 = selected_points[0]
+	var v1 : Vector3 = selected_points[1]
+
+	for i in range(2, selected_points.size()):
+		var v2 : Vector3 = selected_points[i]
+		
+		st.add_uv(Vector2(0, 1))
+		st.add_vertex(v0)
+		st.add_uv(Vector2(0.5, 0))
+		st.add_vertex(v1)
+		st.add_uv(Vector2(1, 1))
+		st.add_vertex(v2)
+		
+		var flip : bool = is_normal_similar(v0, v1, v2, last_known_camera_facing)
+
+		var im3 : int = (i - 2) * 3
+
+		if !flip:
+			st.add_index(im3)
+			st.add_index(im3 + 1)
+			st.add_index(im3 + 2)
+		else:
+			st.add_index(im3 + 2)
+			st.add_index(im3 + 1)
+			st.add_index(im3)
+
+	st.generate_normals()
+	
+	merge_in_surface_tool(mdr, st)
+
 # Appends a triangle to the mesh. It's created from miroring v2 to the ev0, and ev1 edge
 static func append_triangle_to_tri_edge(mdr : MeshDataResource, ev0 : Vector3, ev1 : Vector3, v2 : Vector3) -> void:
 	var vref : Vector3 = reflect_vertex(ev0, ev1, v2)